WO2017152354A1

WO2017152354A1 - An electron-donating unit, a copolymer thereof and their preparation methods, as well as their uses

Info

Publication number: WO2017152354A1
Application number: PCT/CN2016/075839
Authority: WO
Inventors: Xugang GUO; Xiaojie GUO; Qiaogan LIAO; Yongye Liang
Original assignee: South University Of Science And Technology Of China
Priority date: 2016-03-08
Filing date: 2016-03-08
Publication date: 2017-09-14

Abstract

An electron-donating unit of the Formula, a copolymer thereof and their preparation methods, as well as their uses in thin-film transistor or polymer solar cell. The electron-donating unit is an effective building block for constructing high-performance polymer semiconductors due to its solubilizing ability, centrosymmetric geometry, backbone planarity, compact packing, and appropriate electron donating ability versus the previously reported BTOR and DTP units.

Description

An electron-donating unit, a copolymer thereof and their preparation methods, as well as their uses

FIELD

The present invention belongs to the field of semiconductor material, in particular to an electron-donating unit, a copolymer thereof and their preparation methods, as well as their uses.

BACKGROUND

Polymer semiconductors have received great attention due to their potential for fabricating diverse opto-electrical devices using solution-based processing techniques, such as coating and printing^1-3. The solution processability enables the fabrication of cost-effective, large area, and mechanically flexible electronic devices, such as organic thin-film transistors (OTFTs) and polymer solar cells (PSCs) ^2, 4-6. In order to achieve optimal performance while maintaining straightforward, scalable device fabrication, the semiconducting materials should possess well-tailored bandgaps, energetically optimized frontier molecular orbitals (FMOs) , a desirable film morphology, and good solubility^4, 7-15. However, designing and realizing organic semiconductors which can synergistically integrate these performance enhancing parameters without sacrificing materials processability presents a great challenge.

To achieve such processability, polymer semiconductors are typically functionalized with solubilizing alkyl side chain substituents. However, the alkylation patterns must be strategically manipulated to minimize steric hindrance, hence head-to-head (HH) linkages should be avoided in semiconducting polymer design to minimize accompanying backbone torsion, which reduces conjugation along the polymer chain, compromises film crystallinity/order, and diminishes charge carrier mobility^16-19.

In order to achieve high degrees of macromolecular backbone planarity for enhanced charge carrier delocalization, the backbone must be designed to energetically favor planar conformations versus any twisted alternatives. Although in principal conjugated backbones should be energetically favored in planar conformations, adverse steric interactions, mainly from side substituents, often prevent realization of this ideal case. To achieve enhanced planarity，conjugation, and mobility, two materials design strategies are widely employed in polymer electronics, 1) reducing steric hindrance by inserting spacers (or bridges) along the chain^17, 20, and 2) conformation locking with covalent bonds^21, 22 or non-covalent.

The strategy of inserting spacers (Formula 1) , mainly unsubstituted thiophene (or thiazole) derivatives, has yielded great success in high-performance semiconductors such as PBTTT and PQT^20, 23-27. However, the spacer incorporation requires additional steps in the monomer synthesis^28-30 and could also dilute the concentration of key building blocks, typically the acceptor units, in the polymeric backbones, risking sub-optimal opto-electronic properties for the resulting semiconductors^31-34. Moreover, such spacers are typically nonalkylated, which could reduce polymer solubilities^17, 35, 36.

Conformation locking through covalent bonds (Formula 2) has also provided great success as a planarizining design strategy, however, the sp³ orbital hybridization of the bridging atoms, such as C, Si, and Ge, leads to out-of-plane substituent orientation, thereby enlarging intermolecular stacking distances, reducing interchain π-π orbital overlap, and lowering carrier mobilities^21, 22, 37. Therefore, polymer semiconductors containing cyclopentadithiophene or dithienosilole (germole) frequently have limited OTFT mobilities and suboptimal fill factors (FFs； < 70％) in bulk heterojunction (BHJ) PSCs^38-41.

Poly (3, 4-ethylenedioxythiophene) (PEDOT) is a widely used conducting polymer with high doped state conductivity^42, 43 which is partially attributed to substantial backbone planarity⁴⁴. From the crystal structure of 2, 2-bis (3, 4-ethylenedioxythiophene) , the distance between the (thienyl) sulfur and (3, 4-ethylenedioxy) oxygen atoms (S…O) is

substantially below the sum of the S and O van der Waals radii

This intramolecular non-covalent S…O interaction promotes a planar backbone conformation and charge carrier delocalizations^41, 46, 47.

Inspired by the success of PEDOT, we first reported a HH linkage containing donor unit, 3, 3’ -dialkoxy-2, 2’ -bithiophene (BTOR, Figure 1b) ⁴⁸, via employing a dual strategy of reducing the steric bulk of the side chain fragment closest to the conjugated system by replacing a CH₂ fragment with a less bulky O group and utilizing the intramolecular non-covalent (thienyl) S… (alkoxy) O interaction^49-56 to help planarize the backbone. Incorporating BTOR units into polymers affords semiconductors (Formula 3) with small bandgaps, close intermolecular packing, substantial hole mobility of ～0.2 cm²/Vs, and excellent solubility from the high density of alkyl substituent chains⁵⁷. The results demonstrate that strategically utilizing alkoxy side chains and employing the intramolecular non-covalent S…O interaction is an effective strategy for organic electronic materials design^46, 50, 51.

Unfortunately, highly electron-rich BTOR significantly elevates the resulting copolymer HOMOs, and such semiconductors suffer from unsatisfactory air stability in OTFTs⁵⁸ and small open-circuit voltages (V_ocs < 0.6 V) in PSCs, severely limiting BTOR materials applicability^59-61.

Note that Yoshimura developed an electron rich 5H-dithieno [3, 2-b: 2’ , 3’ -d] pyran (DTP, Figure 1c) ⁶², which has greater electron-donating capacity than cyclopentadithiophene⁶³. When copolymerized with difluorobenzothiadiazole, the resulting polymer semiconductor exhibits a smaller bandgap than the cyclopentadithiophene counterpart but maintains a decent V_oc of 0.7 V. The PSCs show promising power conversion efficiencies (PCEs) of 8.0％⁶² and 10.6％⁶⁴ in single junction and tandem cells, respectively. However, the DTP synthesis is tedious and PSC performance is limited by the small FF (63％) due to the low mobility of the DTP polymer, likely attributable to the out-of-plane orientation of the solubilizing substituents and asymmetric DTP structure.

SUMMARY

In order to overcome the defects raised by BTOR and DTP-based copolymers, the present invention provides the design and synthesis of the novel electron-donating 3-alkyl-3’ -alkoxy-2, 2’ -bithiophene (TRTOR) unit (Figure 1e) and that its incorporation into copolymers affords semiconductors (Formula 4) with good materials solubility, high degrees of backbone planarity, appropriately placed FMOs, and ordered film morphologies.

In order to achieve this purpose, the present invention employs the following technical solutions:

An electron-donating unit of the Formula I,

wherein R¹ is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R² is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R¹ and R² are same or different.

To reduce BTOR electron-donating characteristics, an oxygen is removed from an alkoxy chain to afford the optimized building block TRTOR, which bears one alkoxy and one alkyl chain substituent, and hence a single S…O interaction. From another perspective, TRTOR is a 2H-pyran ring opened DTP, hence TRTOR should have electronic properties comparable to those of DTP. Density functional theory (DFT) computation demonstrates a planar backbone conformation for TTOR unit (Figure 1d) , which is functionalized with a single solubilizing alkoxy chain. The introduction of an extra alkyl chain on the 3-position of thiophene should not be detrimental to the TRTOR backbone planarity. Indeed this is confirmed by the DFT computation, which indicates that a TRTOR-containing HH linkage maintains a planar conformation enabled by the single planarizing alkoxy side chain (Figure 1e) ^46, 50.

In comparison to TTOR, TRTOR is a more promising building block since it contains more solubilizing substituent chains and has a more symmetrical structure. In contrast, the asymmetric single-chain functionalized bithiophene based polymer exhibits poor PSC device performance³². Regarding energetic considerations, TRTOR has a low-lying HOMO at -4.92 eV --0.25 eV below that of BTOR (-4.67 eV) and comparable to that of DTP (-4.97 eV； Figure 1) . Therefore, TRTOR-based copolymers should have lower-lying HOMOs versus the BTOR-based counterparts, which will benefit both OTFT and PSC device performance. Furthermore, the single TRTOR S…O interaction should afford the copolymers with enhanced processability versus the BTOR counterparts due to the weaker non-covalent interactions in the former. In comparison to DTP, TRTOR should have more compact stacking due to the abscence of out-of-plane substituents and pseudo-centrosymmetric geometry⁶⁵. Thus, TRTOR is a promising building block for polymer semiconductor construction due to its planar conformation, solubilizing characteristics, appropriately lying HOMO, and centrosymmetric geometry.

In another aspect, the present invention provides a copolymer of the electron-donating unit described herein having the Formula 4,

wherein R¹ is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R² is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R¹ and R² are same or different, π is an electron-deficient group, n depends on the desired solubility of the copolymer, preferably being 5-80.

Preferably, on the basis of the technical solution provided by the present invention, π is selected from the following group:

wherein R is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms.

To verify the above materials deisgn strategy, phthalimide^10, 57, 66 was chosen as the in-chain acceptor unit for constructing a copolymer semiconductor series. It will be seen that the resulting phthalimide-TRTOR polymers exhibit promising device performance in both ogranic thin-film transistors and polymer solar cells, with the PCE (6.3％) of the phthalimide-TRTOR polymer being among the highest reported to date for phthalimide-based polymers¹⁰. These results demonstrate that a single planarizing alkoxy substituent to reduce steric emcumbrance and an S…O interaction to lock the polymer backbone toward planarity render TRTOR a promising building block for polymer semiconductor construction. Materials structure-property-device performance correlations are established here, and offer useful insights into organic electronics materials design. We believe that more promising performance can be realized by optimizing the chemical structures of TRTOR-based materials.

In another aspect, the present invention provides a preparation method of the electron-donating unit described herein wherein R¹ and R² are straight alkyls comprising:

(1) adding 2-bromo-3-alkoxy-thiophene, an alkali carbonate， an organic solvent and water into a reaction vessel, and purging the mixture with an inert gas；

(2) adding Pd (PPh₃) ₄ and then purging an inert gas, heating the mixture to 40-90 ℃；

(3) adding 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane to the mixture and refluxing the mixture at 40-90 ℃, for example, 45 ℃, 53 ℃, 65 ℃, 74 ℃, 83 ℃ and so on；

(4) extracting the reaction mixture and washing；

(5) concentrating the organic layer and purifying to give the electron-donating unit；

wherein the alkoxy and alkyl both are straight.

Preferably, on the basis of the technical solution provided by the present invention, in step (1) , the mole ratio of the 2-bromo-3-alkoxy-thiophene to the alkali carbonate is 1: 0.5-2, for example, 1: 0.8, 1: 1.2, 1: 1.7 and so on, preferably 1: 0.7-1.5, more preferably 1: 1.

preferably, the ratio of the organic solvent or water to the 2-bromo-3-alkoxy-thiophene is 2-10 mL/mmol, for example, 3 mL/mmol, 5 mL/mmol, 8 mL/mmol and so on, preferably 3-7 mL/mmol； the ratio of the THF or water to the 2-bromo-3-alkoxy-thiophene may be same or different.

preferably, the alkali carbonate is selected from K₂CO₃, Na₂CO₃, Li₂CO₃ or a mixture of at least two of them.

preferably, the organic solvent is selected from THF, EtOH, dioxane, DMF, toluene or a mixture of at least two of them.

preferably, time of the purging is more than 10 minutes, preferably more than 20 minutes, more preferably 30 minutes.

preferably, the mixture is heated to 50-80 ℃, for example, 55 ℃, 57 ℃, 65 ℃, 74 ℃ and so on； preferably to 70 ℃；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them.

preferably, in step (2) , the mole ratio of the Pd (PPh₃) ₄ to the 2-bromo-3-alkoxy-thiophene is 1: 5-20, for example, 1: 7, 1: 11, 1: 16 and so on, preferably 1: 8-15, more preferably 1: 10.

preferably, time of the purging is more than 5 minutes, preferably more than 10 minutes, more preferably 20 minutes.

preferably, the mixture is heated to 50-80 ℃, for example, 55 ℃, 57 ℃, 65 ℃, 74 ℃ and so on； preferably to 70 ℃.

preferably, in step (3) , the 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is added with a mole ratio to the 2-bromo-3-alkoxy-thiophene of 1: 3-15, for example, 1: 4, 1: 7, 1: 14 and so on, preferably 1: 5-10, more preferably 1: 6.3.

preferably, the 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is added dropwise.

preferably, the mixture is refluxed at 50-80 ℃, for example, 55 ℃, 57 ℃，65 ℃, 74 ℃ and so on； preferably at 70 ℃.

preferably, in step (4) , the reaction mixture is extracted with organic solvent, preferably with DCM.

preferably, the washing is conducted with water and brine.

preferably, in step (5) , the concentrating is conducted under reduced pressure.

preferably, the purifying is conducted by column chromatography using petroleum ether as an eluent.

In another aspect, the present invention provides a preparation method of the electron-donating unit described herein wherein R¹ or/and R² is (are) branched alkyl comprising:

(1) adding 2-bromo-3-alkoxy-thiophene, 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane and a solvent into a reaction vessel, and purging the mixture with an inert gas； the solvent is known in the art, such as benzene, toluene and the like, or a mixture of at least two of them；

(2) adding a mixture of [Pd (PPh₃) ₄] , Aliquat, and aqueous alkali carbonate, heating the mixture to 90-150 ℃ for 5-30 h；

(3) cooling the reaction mixture to room temperature,

(4) extracting the reaction mixture and washing the combined organic phases after being extracted and drying the organic phase to mainly remove the water therein；

wherein the alkoxy and alkyl both are branched.

Preferably, on the basis of the technical solution provided by the present invention, in step (1) , the ratio of the 2-bromo-3-alkoxy-thiophene to 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is 1: 0.5-1, preferably 1: 0.7-0.9, more preferably 1: 0.8.

preferably, the mixture is stirred and purged with an inert gas.

preferably, the ratio of the solvent to the 2-bromo-3-alkoxy-thiophene is 10-80 mL/g, preferably 20-50 mL/g.

preferably, in step (2) , the mixture is heated to 100-120 ℃ for 10-20 h, more preferably the mixture is heated to 100-110 ℃ for 13-18 h.

preferably, the Aliquat is in toluene.

preferably, the mass ratio of [Pd (PPh₃) ₄] , Aliquat, and alkali carbonate is 1: 1-5: 2-10, for example, 1: 2: 5, 1: 4: 9, 1: 3: 4 and so on, preferably 1: 2-3: 3-8, more preferably 1: 2.5: 5.

preferably, the washing is conducted with water.

preferably, the drying is conducted over MgSO₄.

preferably, the purifying is conducted by column chromatography or silica gel using petroleum ether as an eluent.

In another aspect, the present invention provides a preparation method of the copolymer described herein comprising:

(1) adding the electron-donating unit of claim 1, an electron-deficient material, tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) , and tris (o-tolyl) phosphine (P (o-tolyl) ₃) into a reaction vessel, and subjecting the reaction vessel and the mixture to an inert gas；

(2) adding an organic solvent； sealing the reaction vessel under an inert gas flow and then stirring while heating；

(3) adding 2- (tributylstanny) thiophene and stirring the reaction mixture while heating；finally, adding 2-bromothiophene and stirring the reaction mixture while heating；

(4) after cooling to room temperature, dripping the reaction mixture into methanol containing hydrochloric acid；

(5) drying the solid precipitate obtained in step (4) to give the crude product, and then extracting the crude product；

(6) after final extraction, concentrating the polymer solution, and then being dripped into methanol, collecting the polymer and drying to give the copolymer. Preferably, on the basis of the technical solution provided by the present invention, in step (1) , the electron-deficient material is selected from the following group:

preferably, the mole ratio of the electron-donating unit of claim 1 to the electron-deficient material is 1: 0.5-2, for example, 1: 0.8, 1: 1.2, 1: 1.8 and so on, preferably 1: 0.8-1.5, more preferably 1: 1.

preferably, the mole ratio of the tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) to tris (o-tolyl) phosphine (P (o-tolyl) ₃) is 1: 4-15, for example, 1: 6, 1: 9, 1: 13 and so on, preferably 1: 6-10, more preferably 1: 8； the Pd loading is 0.005-0.1 equiv, preferably 0.01-0.06.

preferably, the reaction vessel and the mixture are subjected to 1-5 pump/purge cycles with Ar.

preferably, in step (2) , the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them.

preferably, the organic solvent is selected from any one of anhydrous toluene, benzene, chlorobenzene, DMF, or a mixture of at least two of them.

preferably, the ratio of the organic solvent to the electron-donating unit is 10-75 mL/mmol, preferably 5-50 mL/mmol.

preferably, the heating is conducted at 50-170 ℃ for 1-72h, preferably at 80-150 ℃ for 3-50h.

preferably, the heating is conducted under microwave irradiation.

preferably, the heating is conducted by 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation.

preferably, in step (3) , the heating is conducted at 80-170 ℃ for more than 0.2 h, preferably at 100-160 ℃ for more than 0.4 h.

preferably, the heating is conducted under microwave irradiation.

preferably, the heating is conducted under microwave irradiation at 140 ℃ for 0.5 h；finally, adding 2-bromothiophene and stirring the reaction mixture at 140 ℃ for another 0.5 h.

preferably, the mole ratio of the 2- (tributylstanny) thiophene to the electron-donating unit is 0.1-0.5: 1, for example, 0.2: 1, 0.4: 1 and so on, preferably 0.2: 0.4-1.

preferably, the mole ratio of the 2-bromothiophene to the electron-donating unit is 0.2-1.5: 1, for example, 0.4: 1, 0.8: 1, 1.3: 1 and so on, preferably 0.4: 0.8-1； preferably, in step (4) , the methanol contains 0.5-10mL hydrochloric acid，preferably 0.5-10mLof 5-20 mol/L hydrochloric acid.

preferably, the dripping is conducted under vigorous stirring, preferably is conducted for at least 0.5 h, preferably at least 1 h.

preferably, in step (6) , the dripping is conducted under vigorous stirring.

preferably, the collecting is conducted by filtration.

preferably, the drying is conducted under reduced pressure.

In still another aspect, the present invention provides an use of the copolymer according to the present invention in thin-film transistor or polymer solar cell.

The raw material used in above preparation method can be prepared by known method in the art or by the following method described below or buying on the market.

We report here the design and synthesis of a simple head-to-head linakge containing electron-donating 3-alkyl-3’ -alkoxy-2, 2’ -bithiophene (TRTOR) unit for constructing high-performance polymer semiconductors. In comparison to the 3, 3’ -dialkoxy-2, 2’ -bithiophene (BTOR) unit having two alkoxy substituents, which utilizes the reduced steric hindrance of the O (versus CH₂) and conformation locking effect of intramolecular S…O non-covalent interactions to induce backbone planarity, TRTOR reported here has a single planarizing alkoxy substituent hence an optimized single S…O interaction. Replacement of one alkoxy substituent with a less electron-donating alkyl substituent yields TRTOR polymers with lower-lying HOMOs and increased solubility without sacrificing backbone planarity due to the weaker single S…O interaction. From another perspective, alike pyran ring-opened 5H-dithieno [3, 2-b: 2’ , 3’ -d] pyran (DTP) , TRTOR has comparable electronic properties but a centrosymmetric geometry, promoting a more compact and ordered structure than DTP, which is axisymmetric with out-of-plane substituents.

Copolymerizing TRTOR with electron-deficient phthalimides yields copolymers with promising organic thin-film transistor and polymer solar cell performance. The power conversion efficiency (6.3％) of the TRTOR polymer is the highest among all phthalimide-based polymers reported to date. These results demonstrate that TRTOR is an effective building block for constructing high-performance polymer semiconductors due to its solubilizing ability, centrosymmetric geometry, backbone planarity, compact packing, and appropriate electron donating ability versus the previously reported BTOR and DTP units. Hence, a head-to-head linkage containing one alkyl chain and one alkoxy substituent at the bithiophene 3-positions can achieve planar backbones due to reduced steric hindrance and intramolecular non-covalent S…O interactions, and strategically employing single S…O interactions is thus a promising strategy for materials design in organic electronics.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 are chemical structures, optimized geometries, and energy levels of the frontier molecular orbitals of (a) 3, 3’ -dialkyl bithiophene (BTR) ； (b) 3, 3’ -dialkoxy bithiophene (BTOR) ； (c) 5H-dithieno [3, 2-b: 2’ , 3’ -d] pyran (DTP) ； (d) 3-alkoxy-2, 2’ -bithiophene (TTOR) , and (e) 3-alkyl-3’ -alkoxy-2, 2’ -bithiophene (TRTOR) ； calculations carried out at the DFT//B3LYP/6-31G**level, alkyl substituents truncated here to simplify the calculations.

Figure 2. (a) Optical absorption spectra of polymer films of P1-P5； (b) Cyclic voltammograms of P1-P5 films in 0.1 M (n-Bu) ₄N^. PF₆ acetonitrile solution (the Fc/Fc⁺ redox couple was used as an internal standard) .

Figure 3. DSC thermograms of the polymers P1-P5 at a temperature ramp rate of 10 ℃/min under N₂. The top line is from the first cooling run and the bottom line is from the second heating run.

Figure 4. Transfer curves of P2 and P5 organic thin-film transistors at (a) the linear (V_d ＝ -10V) and (b) saturation region (V_d＝ -80V) ； (c) J-V characteristics of the optimized inverted polymer solar cells of P1-P5 under simulated AM 1.5 G illumination (100 mW cm^-2) .

Figure 5. In-plane (q_xy) and out-of-plane (q_z) line cuts of the GIWAXS images for the neat polymer films prepared on octyldecyltrichlorosilane (OTS) -modified Si substrate. The spectra are split in order to better view the (100) lamellar interactions (left) and the (010) π-π interactions (right) .

Figure 6. GIWAXS images of polymers blended with PC₇₁BM and processed with 3％ODT additive.

Figure 7. TEM images of P1 (aand h) , P2 (b and i) , P3 (c and j) , P4 (d and k) , P5a (e and l) , P5b (f and m) , and P5c (g and n) bulk heterojunction blend (polymer: PC₇₁BM) films processed without (up row) and with (bottom row) processing additive, 1, 8-octanedithiol (ODT) . (Scale bar: 500 nm) .

Figure 8. UV-Vis absorption spectra of polymers P1-P5 in chloroform solution (1 × 10^-5 M) .

Figure 9. Thermogravimetric analysis of polymers P1-P5 at temperature ramp rate of 10 ℃/min.

Figure 10. Computed optimized geometry for the repeating units of DTP-based polymer P3 (a) and TRTOR-based polymer P5 (b) . The calculations were carried out at the DFT//B3LYP/6-31G**level, alkyl substituents are truncated here to simplify the calculations.

Figure 11. J-V characteristics of the inverted polymer solar cells of P2-P5 under simulated AM 1.5 G illumination (100 mW cm^-2) , the cells has the same composition with the optimized PSCs but without using processing additive, 1, 8-octanedithiol.

Figure 12. External quantum efficiency (EQE) of polymer soar cells of P2, P3, and P5 fabricated under optimized conditions.

Figure 13. 2D GIWAXS images for thermal annealed neat polymer films deposited on octyldecyltrichlorosilane modified Si substrate.

Figure 14. 2D GIWAXS images for polymer: PC₇₁BM blend films without using processing additive.

Figure 15. Out-of-plane (q_z) and in-plane (q_xy) line cuts cuts of the GIWAXS for blend films without (solid) and with (dashed) 3％ (v/v) ODT as the processing additive.

Figure 16. AFM topographical images of polymer: PC₇₁BM blend films of P1 (a, h) , P2 (b, i) , P3 (c, j) , P4 (d, k) , P5a (e, l) , P5b (f, m) and P5c (g, n) processed without (1^st and 2^nd rows) and with (3^rd and 4^th rows) additive, 1, 8-octanedithiol. The image size is 5 μm × 5 μm.

Figure 17. UV-Vis absorption spectra of polymers P1’ -P6’ in thin films.

Figure 18. UV-Vis absorption spectra of polymers P1’ -P6’ in chloroform solution (1 ×10^-5 M) .

Figure 19. J-V curves of the photovoltaic devices based on the five polymers with PC₇₁BM.

DETAILED DESCRIPTION

To facilitate understanding of the present invention, the embodiment of the present invention is exemplified as follows. Skilled in the art should be appreciated that the embodiments are merely used to help understand the present invention and should not be regarded as specific limits on the invention.

All reagents and chemicals were commercially available and were used without further purification unless otherwise stated. Tetrahydrofuran and toluene were distilled from Na/benzophenone, and anhydrous dichloromethane and acetonitrile were distilled from CaH₂. The known monomers N-dodecyl-3, 6-dibromophthalimide⁸⁷, N- (2-ethylhexyl) -3, 6-dibromophthalimide⁸⁷ were prepared by following the published procedure, and N-octyl-3, 6-dibromophthalimide was synthesized via the same procedure from 3, 6-dibromophthalic anhydride and n-octylamine. The monomer (5, 5-bis (3, 7-dimethyloctyl) -5H-dithieno [3, 2-b: 2’ , 3’ -d] pyran-2, 7-diyl) bis (tributylstan nane) was purchased from SunaTech Inc. (Suzhou, Jiangsu) , and 5, 5’ -bis (trimethylstannyl) -3, 3’ -bis (dodecyl-oxy) -2, 2’ -bithiophene was synthesized via the published procedures⁸⁸. All other reagents were used as received except where noted. Unless otherwise stated, all manipulations and reactions were carried out under argon using standard Schlenk line techniques. Polymerizations were carried out on Initiator+ Microwave Synthesizer (Biotage, Sweden) .

¹H and ¹³C spectra were recorded on a Bruker Ascend 400MHz spectrometer. Chemical shifts were referenced to residual protio-solvent signals. C, H, N, S elemental analyses (EA) of monomers and polymers were performed at Shenzhen University (Shenzhen, Guangdong) . Polymer molecular weights were measured on Polymer Laboratories GPC-PL220 high temperature GPC/SEC system at 170 ℃ vs polystyrene standards using trichlorobenzene as eluent. DSC curves were recorded on a differential scanning calorimetry (Mettler, STAR^e, heating rate ＝ 10 ℃/min, nitrogen purge) . TGA curves were recorded on a TA Instrument (Mettler, STAR^e) . UV-Vis data were recorded on a Shimadzu UV-3600 UV-VIS-NIR spectrophotometer. Cyclic voltammetry measurements of polymers were carried out under argon atmosphere using a CHI760E voltammetric analyzer with 0.1 M tetra-n-butylammonium hexafluorophosphate in acetonitrile as supporting electrolyte. A platinum disk working electrode, a platinum wire counter electrode and silver wire reference electrode were employed, and F_c/F_c+ was used as internal reference for all measurements. The scan rate was 100 mV/S. Polymer films were drop-coated from chloroform solutions on a Pt working electrode (2 mm in diameter) . The supporting electrolyte solution was thoroughly purged with Ar before all CV measurements. AFM measurements of polymer: PCBM blend films were performed by using a Dimension Icon Scanning Probe Microscope (Asylum Research, MFP-3D-Stand Alone) in tapping mode. TEM specimens were prepared following identical conditions as the actual devices, but were drop-cast onto 40 nm PEDOT: PSS covered substrate. After drying, substrates were transferred to deionized water and the floated films were transferred to TEM grids. TEM images were obtained on Tecnai Spirit (20 kV) TEM.

The synthesis of the key TRTOR building block is straightforward, and Scheme 1 depicts the Synthesis of TRTOR monomer and TRTOR-based polymers P5. The BTR(seeing Figure 1a) , BTOR, DTP, and TTOR-based polymers P1-P4 were also synthesized for comparison. The intramolecular non-covalent S…O interaction is marked by dash line.

Reagents/conditions in Scheme 1 are: (i) NBS, chloroform, HOAc； (ii) n-BuLi, isopropoxyboronic acid pinacol ester, THF； (iii) ROH, PTSA, toluene, 110 ℃； (iv) NBS, DMF； (v) Pd (PPh₃) ₄, K₂CO₃, THF, H₂O； (vi) n-BuLi, Me₃SnCl, THF (vii) Pd₂ (dba) ₃, P (o-tolyl) ₃, toluene, microwave, 140 ℃.

More detailed monomer and polymer synthetic and characterization information is reported as follows. Dioxaborolane 3⁶⁷ and brominated thiophene 6⁴⁸ were synthesized following published procedures. Suzuki coupling between 3 and 6 affords monomer precursor 7 in good yield (> 60％) , with subsequent lithiation and quenching with Me₃ SnCl providing monomer 8 in good purity. After further purification via recrystallization from isopropyl alcohol, 8 was copolymerized with the imide-functionalized arene, dibromophthalimide^57, 66, under a typical Stille polymerization protocol using microwaves for heating (Scheme 1) .

Monomer and Polymer Synthesis-wherein R is a linear alkane

3a: 2- (3-dodecylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane synthesized by following Scheme 2

Commercial available 2-bromo-3-dodecyl-thiophene 2a (4.0 g, 12.07 mmol) was added into an oven dried flask and then dissolved in 90 mL anhydrous THF under argon. After cooling to -78 ℃, n-BuLi (13.28 mmol, 8.30 mL, 1.6 M in hexane) was added dropwise and the whole was stirred at -78 ℃ for 50 min. Then 2-isopropoxy-4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane (2.47 g, 13.28 mmol) was added in one portion and the reaction mixture was warmed to room temperature and stirred overnight. The reaction was quenched with 30 mL water and the mixture was diluted with diethyl ether. The aqueous phase was extracted with diethyl ether twice and the combined organic phase was washed with brine once and dried over sodium sulfate. After removal of solvent under reduced pressure, the crude product was subjected to column chromatography using hexane: dichloromethane (DCM) ＝ 4: 1 as eluent to afford 3a as a liquid (2.3 g, 50 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.49 (d, 1H) , 7.03 (d, 1H) , 2.89 (t, 2H) , 1.59 (m, 2H) , 1.27-1.34 (m, 30H) , 0.90 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 154.65, 131.20, 130.23, 83.44, 31.87, 31.77, 30.06, 29.65, 29.61, 29.58, 29.41, 29.31, 29.24, 24.72, 24.51, 22.64, 14.07.

5a: 3- (undecyloxy) thiophene synthesized by following Scheme 3

A mixture of 3-methoxythiophene 4 (10.00 g, 87.60 mmol) , undecan-1-ol (30.2 g, 175.2 mmol) , p-toluenesulfonic acid monohydrate (1.67 g, 0.1 eq) and 65 ml toluene was heated in a 110 ℃ bath overnight under argon. After dichloromethane/water extraction, the organic phase was dried over MgSO₄. The solvent was then removed by rotvap, and the residue was purified by column chromatography (silica gel) using petroleum ether as eluent to give 5a as a colorless oil (13.8 g, 62 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.17 (dd, 1H) , 6.75 (dd, 1H) , 6.29 (dd, 1H) , 3.93 (t, 2H) , 1.92-1.65 (m, 2H) , 1.51-1.11 (m, 16H) , 0.88 (t, 3H) .

6a: 2-bromo-3- (undecyloxy) thiophene synthesized by following Scheme 4

NBS (1.83 g, 10.29 mmol) was added in one portion to 5a (2.5 g, 9.8 mmol) in 20 mL DMF at 0 ℃ and the whole was warmed to room temperature and stirred for 15 h. The reaction mixture was diluted with ether (50 mL) and washed with water (2 × 20 mL) . The organic layer was dried over MgSO₄, concentrated under reduced pressure, and the residue was subjected to column chromatography (silica gel, petroleum ether) to give 6a as a colorless solid (3.02 g, 92.4 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.19 (d, 1H) , 6.74 (d, 1H) , 4.03 (t, 2H) , 1.85-1.62 (m, 2H) , 1.52-1.14 (m, 16H) , 0.88 (t, 3H) .

7a: 3-dodecyl-3' - (undecyloxy) -2, 2' -bithiophene synthesized by following Scheme 5

An oven-dried two necked 100 mL round bottom flask were equipped with a condenser and cooled under Ar protection. To the flask was added 2-bromo-3- (undecyloxy) -thiophene 6a (0.5 g, 1.5 mmol) , K₂CO₃ (0.207 g, 1.5 mmol) , THF (7 mL) and H₂O (7 mL) , and the whole was purged with Ar for 30 minutes. Pd (PPh₃) ₄ (0.173 g, 0.15 mmol) was then added followed by Ar purging for 20 minutes. The reaction mixture was then heated to 70 ℃. 2- (3-dodecylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane 3a (0.568 g, 1.5 mmol) was added dropwise and the solution was refluxed at 70 ℃ overnight. The reaction mixture was extracted with DCM and washed with water and brine. The organic layer was concentrated under reduced pressure and purified by column chromatography using petroleum ether as the eluent to give a yellowish solid (0.47 g, 62 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.22 (d, 1H) , 7.18 (d, 1H) , 6.91 (d, 1H) , 6.87 (d, 1H) , 4.00 (t, 2H) , 2.74-2.62 (t, 2H) , 1.77-1.66 (m, 2H) , 1.64-1.55 (m, 2H) , 1.45-1.16 (m, 34H) , 0.88 (t, 6H) .

8a: 3-dodecyl-3' - (undecyloxy) -5, 5’ -bis (trimethylstannyl) -2, 2' -bithiophene synthesized by following Scheme 6

3-dodecyl-3' - (undecyloxy) -2, 2' -bithiophene 7a (224 mg, 0.44 mmol) and 5 mL dry THF was added to a flask. The resulting clear solution was cooled to -78 ℃ using dry ice/acetone bath. Then 0.67 mL n-BuLi solution in hexane (1.07 mmol, 1.6 mol/L) was added dropwise. After stirring at -78 ℃ for 1 h and room temperature for 1 h, 1.15 mL trimethyltin chloride (1.15 mmol, 1 mol/L) was added in one portion, and then the cooling bath was removed. After being stirred at ambient temperature for 4 h, the reaction mixture was quenched with water carefully and then poured into cool water and extracted with diethyl ether for twice. After removal of organic solvent, the monomer was obtained as a yellowish oil, which was further purified by recrystallization in isopropyl alcohol to provide the product as pale solid (0.35 g, 95％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.01 (s, 1H) , 6.88 (s, 1H) , 4.03 (t, 2H) , 2.69-2.73 (t, 2H) , 1.70-1.76 (m, 2H) , 1.60-1.64 (m, 2H) , 1.25-1.45 (m, 34H) , 0.88 (t, 6H) , 0.28-0.38 (m, 18H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 154.76, 141.15, 137.21, 136.13, 135.34, 134.16, 124.94, 119.85, 71.92, 32.00, 30.81, 29.86, 29.78, 29.76, 29.74, 29.72, 29.58, 29.50, 29.44, 29.42, 26.13, 22.76, 14.20, -8.22, -10.06. Anal. Calcd for C₃₇H₆₈OS₂Sn₂ (％) : C, 53.51； H, 8.25； N, 0； S, 7.72. Found (％) : C, 53.89； H, 8.47； N, 0.02； S, 7.83.

3b: 4, 4, 5, 5-tetramethyl-2- (3-octylthiophen-2-yl) -1, 3, 2-dioxaborolane synthesized by following Scheme 7

4, 4, 5, 5-tetramethyl-2- (3-octylthiophen-2-yl) -1, 3, 2-dioxaborolane was synthesized following the same procedure employed in synthesis of compound 3a. After column chromatography, the product was obtained as an oil (57 ％) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.49 (d, 1H) , 7.02 (d, 1H) , 2.98-2.83 (t, 2H) , 1.60 (m, 2H) , 1.36-1.25 (m, 22H) , 0.89 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 154.72, 131.29, 130.30, 83.52, 31.95, 31.85, 30.15, 29.45, 29.33, 24.80, 22.72, 14.15.

5b: 3- (heptyloxy) thiophene synthesized by following Scheme 8

3- (heptyloxy) thiophene 5b was synthesized following the same procedure employed in synthesis of compound 5a, and the product was obtained as a colorless oil (61 ％) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.17 (dd, 1H) , 6.76 (dd, 1H) , 6.23 (dd, 1H) , 3.94 (t, 2H) , 1.78 (m, 2H) , 1.50-1.24 (m, 8H) , 0.91 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 158.08, 124.53, 119.57, 96.95, 70.29, 31.81, 29.31, 29.10, 26.05, 22.65, 14.12.

6b: 2-bromo-3- (heptyloxy) thiophene synthesized by following Scheme 9

2-bromo-3- (heptyloxy) thiophene 6b was synthesized following the same procedure employed in the synthesis of compound 6a. After purification over column chromatography (silica gel, petroleum ether) , the product was obtained as a colorless oil (92 ％) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.20 (d, 1H) , 6.76 (d, 1H) , 4.05 (t, 2H) , 1.76 (m, 2H) , 1.51-1.23 (m, 8H) , 0.90 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 154.58, 124.13, 117.55, 91.62, 72.28, 31.62, 29.51, 29.03, 25.81, 22.62, 14.11.

7b: 3- (heptyloxy) -3' -octyl-2, 2' -bithiophene synthesized by following Scheme 10

3- (heptyloxy) -3' -octyl-2, 2' -bithiophene was synthesized following the same procedure employed in synthesis of compound 7a. After purification over column chromatography, the product was obtained as pale oil (61 ％) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.23 (d, 1H) , 7.19 (d, 1H) , 6.93 (d, 1H) , 6.88 (d, 1H) , 4.02 (t, 2H) , 2.75-2.66 (t, 2H) , 1.80-1.69 (m, 2H) , 1.61 (m, 2H) , 1.47-1.20 (m, 18H) , 0.95-0.84 (m, 6H) . ¹³C NMR (100 MHz, CDCl₃, ppm) δ 153.54, 140.53, 128.85, 127.80, 124.38, 123.11, 117.57, 113.56, 71.97, 31.89, 30.63, 29.67, 29.63, 29.51, 29.47, 29.34, 29.06, 25.94, 22.74, 22.65, 14.17, 14.14.

8b: 3-octyl-3' - (heptyloxy) -5, 5’ -bis (trimethylstannyl) -2, 2' -bithiophene synthesized by following Scheme 11

3-octyl-3' - (heptyloxy) -5, 5’ -bis (trimethylstannyl) -2, 2' -bithiophene 8b was synthesized following the same procedure employed in the synthesis of monomer 8a. After recrystallization in isopropyl alcohol at ～0 ℃, the monomer was obtained as a yellowish solid (92％) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 6.99 (s, 1H) , 6.89 (s, 1H) , 4.04 (t, 2H) , 2.73 (t, 2H) , 1.73 (m, 2H) , 1.61 (m, 2H) , 1.48-1.21 (m, 18H) , 0.87 (m, 6H) , 0.46-0.27 (m, 18H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 154.75, 141.13, 137.18, 136.11, 135.31, 134.16, 124.94, 119.87, 71.91, 31.95, 31.88, 30.77, 29.81, 29.74, 29.48, 29.40, 29.34, 29.11, 26.06, 22.72, 22.67, 14.17, 14.15, -8.25. Anal. Calcd for C₂₉H₅₂OS₂Sn₂ (％) : C, 48.49； H, 7.30； N, 0； S, 8.93. Found (％) : C, 49.08； H, 7.46； N, 0.02； S, 9.05.

9: 3, 3’ -didodecyl-2, 2’ -bithiophene synthesized by following Scheme 12

Known compound 9 was prepared and isolated via the published procedure (Kumada coupling of dodecyl magnesium bromide and 3, 3’ -dibromo-2, 2’ -bithiophene) as a colorless solid (92 ％) after column chromatography². ¹H NMR (CDCl₃, 400 MHz, ppm) : δ 7.29 (d, 2H) , 6.97 (d, 2H) , 2.50 (t, 4H) , 1.51-1.57 (m, 4H) , 1.23-1.32 (m, 36H) , 0.88 (t, 6H) . ¹³C NMR (CDCl3, 100 MHz, ppm) : δ 142.56, 128.93, 128.74, 125.43, 32.15, 30.94, 29.91, 29.89, 29.79, 29.67, 29.65, 29.59, 29.00, 22.92, 14.35.

10: 5, 5’ -bis (trimethylstannyl) -3, 3’ -didodecyl-2, 2’ -bithiophene synthesized by following Scheme 13

Monomer 10 was prepared and isolated as a colorless oil from 9 using the same procedures employed for monomer 8a (82 ％) . ¹H NMR (CDCl₃, 400MHz, ppm) : δ 7.03 (s, 2H) , 2.52 (t, 4H) , 1.56 (m, 4H) , 1.25 (m, 36H) , 0.90 (t, 6H) , 0.38 (s, 18H) . ¹³CNMR (CDCl3, 100 MHz, ppm) : δ 142.84, 137.31, 136.83, 135.17, 31.97, 30.98, 29.72, 29.63, 29.49, 29.41, 28.77, 22.73, 14.16, -8.20 Anal. Calcd for C₃₈H₇₀S₂Sn₂ (％) : C, 55.09； H, 8.52； N, 0； S, 7.74.

11: 3- (dodecyloxy) -2, 2' -bithiophene synthesized by following Scheme 14

An oven-dried two necked 100 mL round bottom flask containing a stir bar were equipped with a condenser and cooled under Ar. To the flask was added 2-bromo-3- (dodecyloxy) thiophene (1.02 g, 2.94 mmol) , K₂CO₃ (0.406 g, 2.94 mmol) , 15 mL THF and 15 mL H₂O, followed by purging with Ar for 30 minutes. Pd (PPh₃) ₄ (0.340 g, 0.294 mmol) was then added and purged with Ar for 20 minutes. The whole was heated to 70 ℃. The commercial available 4, 4, 5, 5-tetramethyl-2- (thiophen-2-yl) -1, 3, 2-dioxaborolane (0.617 g, 2.94 mmol) was added dropwise and the solution was refluxed at 70 ℃ overnight. The reaction was cooled to room temperature and the organic layer was extracted with CH₂Cl₂ and washed with water and brine. The organic layer was concentrated under reduced pressure via rotvap and purified by column chromatography using petroleum ether as the eluent to yield a colorless oil (0.515 g, 50 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) δ 7.26 (dd, 1H) , 7.23 (dd, 1H) , 7.08, 7.03 (dd, 1H) , (dd, 1H) , 6.87 (d, 1H) , 4.13 (t, 2H) , 1.86 (m, 2H) , 1.55 (m, 2H) , 1.38 (m, 16H) , 0.92 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 152.56, 135.36, 126.72, 123.51, 122.45, 121.35, 117.48, 115.48, 71.91, 31.99, 29.73, 29.72, 29.65, 29.61, 29.42, 29.40, 26.07, 22.76, 14.19.

12: 3-dodecyloxy-5, 5’ -bis (trimethylstannyl) -2, 2’ -bithiophene synthesized by following Scheme 15

Monomer 12 was synthesized following the same procedure employed in synthesis of compound 8a. ¹H NMR (400MHz, CDCl₃, ppm) : 7.37 (d, 1H) , 7.11 (d, 1H) , 6.91 (s, 1H) , 4.15 (t, 2H) , 1.87 (m, 2H) , 1.56 (m, 2H) , 1.35 (m, 16H) , 0.91 (t, 3H) , 0.40 (s, 18H) . ¹³C NMR (100MHz, CDCl₃, ppm) : δ 153.91, 141.05, 135.19, 134.90, 133.95, 124.81, 123.56, 121.08, 71.71, 31.88, 29.73, 29.66, 29.61, 29.39, 29.33, 26.09, 22.65, 14.09, -6.47, -8.32, -10.17. Anal. Calcd for C₂₆H₄₄OS₂Sn₂ (％) : C, 46.32； H, 6.58； N, 0； S, 9.51.

13: N-octyl-3, 6-dibromophthalimide synthesized by following Scheme 16

3, 6-dibromo phthalic anhydride (1.53 g, 5 mmol) , n-octylamine (0.84 g, 6.5 mmol) and glacial acetic acid (30 ml) were combined and refluxed under Ar for 2 h. After the acetic acid was removed under reduced pressure, the target compound 13 was purified via column chromatography (silica gel, dichloromethane: hexanes 1: 2) . The resulting white solid was further purified via recrystallization from hexanes to afford a white crystal as the product (1.88 g, 90 ％) .

¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.64 (s, 2H) , 3.73-3.61 (t, 2H) , 1.74-1.63 (m, 2H) , 1.29 (m, 10H) , 0.86 (t, 3H) . ¹³C NMR (100 MHz, CDCl₃, ppm) : δ 164.87, 139.49, 131.31, 117.50, 38.68, 31.78, 29.11, 28.32, 26.84, 22.63, 14.10. Anal. Calcd for C₁₆H₁₉Br₂NO₂ (％) : C, 46.07； H, 4.59； N, 3.36； S, 0. Found (％) : C, 46.08； H, 4.47； N, 3.23； S, 0.03.

General Procedure for Polymerizations via Stille Coupling for Synthesis of Polymers P1-P5.

An glass tube was charged with two monomers (0.2 mmol each) , tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) _, and tris (o-tolyl) phosphine (P (o-tolyl) ₃) (1: 8, Pd₂ (dba) ₃: P (o-tolyl) ₃ molar ratio； Pd loading: 0.03-0.05 equiv) . The tube and its contents were subjected to 3 pump/purge cycles with argon, followed by the addition of anhydrous toluene (6-8 mL) via syringe. The tube was sealed under argon flow and then stirred at 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation. Then, 0.1 mL of 2- (tributylstanny) thiophene was added and the reaction mixture was stirred under microwave irradiation at 140 ℃ for 0.5 h. Finally, 0.2 mL of 2-bromothiophene was added and the reaction mixture was stirred at 140 ℃ for another 0.5 h. After cooling to room temperature, the reaction mixture was slowly dripped into 100 mL of methanol (containing 5 mL 12 N hydrochloric acid) under vigorous stirring. After stirring for 4h, the solid precipitate was transferred to a Soxhlet thimble. After drying, the crude product was subjected to sequential Soxhlet extraction with the choice of solvents and sequence depending on the solubility of the particular polymer. After final extraction, the polymer solution was concentrated to approximately 20 mL, and then dripped into 100 mL of methanol under vigorous stirring. The polymer was collected by filtration and dried under reduced pressure to afford deep colored solid as the product.

P1¹ was synthesized by following Scheme 17.

The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane and chloroform. The polymer was obtained as a yellow solid (114 mg, 68％yield) . ¹H NMR (400 MHz, CDCl₃, ppm) : δ 7.82 (s, 2H) , 7.81 (s, 2H) , 3.72 (br, 2H) , 2.67 (t, 4H) , 1.69 (m, 6H) , 1.25 (m, 54H) , 0.87 (m, 9H) . Anal. Calcd for C₅₂H₇₉NO₂S₂ (％) : C, 76.70； H, 9.78； N, 1.72； S, 7.87.

P2 was synthesized by following Scheme 18.

The solvent sequence for Soxhlet extraction was methanol, acetone, hexane, dichloromethane and chloroform. The polymer was obtained as a blue solid with copper-like metallic luster (108 mg, 64％yield) . ¹H NMR (400 MHz, CDCl₃) : δ 7.97 (br, 4H) , 4.28 (br, 4H) , 3.70 (br, 2H) , 1.99 (br, 4H) , 1.56-1.23 (m, 56H) , 0.94 (m, 9H) . Anal. Calcd for C₅₂H₇₉NO₄S₂ (％) : C, 73.80； H, 9.41； N, 1.66； S, 7.58. Found (％) : C, 73.81； H, 9.72； N, 1.53； S, 7.31.

P3 was synthesized by following Scheme 19.

The solvent sequence for Soxhlet extraction was methanol, acetone, and hexane. This polymer was obtained as brown solid (97 mg, 62％yield) . M_n ＝ 8.1 kDa, PDI ＝3.13. ¹H NMR (400 MHz, CDCl₃) δ 7.76 (dd, 4H) , 3.70 (br, 2H) , 2.12-1.86 (m, 4H) , 1.77-0.98 (m, 40H) , 0.96-0.54 (m, 21H) . Anal. Calcd for C₄₉H₇₁NO₃S₂ (％) : C, 74.86； H, 9.10； N, 1.78； S, 8.16. Found (％) : C, 74.01； H, 9.41； N, 1.60； S, 7.47.

P4 was synthesized by following Scheme 20.

The solvent sequence for Soxhlet extraction was methanol, acetone, hexane and chloroform. The polymer was obtained as a blue solid with copper-like metallic luster (86 mg, 60％yield) . ¹H NMR (400 MHz, CDCl₃) : δ 8.14 –7.41 (m, 4H) , 7.00 (s, 1H) , 4.21 (s, 2H) , 3.59 (s, 2H) , 1.93 (s, 4H) , 1.26 (s, 42H) , 0.86 (s, 12H) . Anal. Calcd for C₄₄H₆₃NO₃S₂ (％) : C, 73.59； H, 8.84； N, 1.95； S, 8.93.

P5a was synthesized by following Scheme 21.

The solvent sequence for Soxhlet extraction was methanol, acetone, and hexane, chloroform. This polymer was obtained as a brown solid (155 mg, 95％yield) . M_n ＝ 29.3 kDa, PDI ＝ 2.14.¹H NMR (400 MHz, CDCl₃) δ 7.96-7.80 (m, 4H) , 4.23 (br, 2H) , 3.71 (br, 2H) , 2.89 (br, 2H) , 1.88 (br, 2H) , 1.75 (br, 2H) , 1.55 (br, 4H) , 1.49-1.02 (m, 50H) , 0.87-0.83 (m, 9H) . Anal. Calcd for C₅₁H₇₇NO₃S₂ (％) : C, 75.04； H, 9.51； N, 1.72； S, 7.85. Found (％) : C, 75.13； H, 9.47； N, 1.63； S, 7.77.

P5b was synthesized by following Scheme 22.

The solvent sequence for Soxhlet extraction was methanol, acetone, and hexane, dichloromethane, and chloroform. This polymer was obtained as a purple solid (102 mg, 79％yield) . M_n ＝ 35.3 kDa, PDI ＝ 1.48.¹H NMR (400 MHz, CDCl₃) δ 7.96-7.79 (m, 4H) , 4.22-3.70 (m, 4H) , 2.87 (s, 2H) , 2.00-1.29 (m, 34H) , 0.88 (s, 9H) . Anal. Calcd for C₃₉H₅₃NO₃S₂ (％) : C, 72.29； H, 8.24； N, 2.16； S, 9.90. Found (％) : C, 72.20； H, 8.57； N, 2.04； S, 9.58.

P5c was synthesized by following Scheme 23.

The solvent sequence for Soxhlet extraction was methanol, acetone, and hexane, dichloromethane, and chloroform. This polymer was obtained as a purple solid (88 mg, 68％yield) . M_n ＝ 18.5 kDa, PDI ＝ 1.91.¹H NMR (400 MHz, CDCl₃) δ 8.03-7.71 (m, 4H) , 4.23 (br, 2H) , 3.62 (br, 2H) , 2.89 (br, 2H) , 1.89 (br, 3H) , 1.75 (br, 2H) , 1.60-1.16 (m, 26H) , 0.88 (d, 12H) . Anal. Calcd for C₃₉H₅₃NO₃S₂ (％) : C, 72.29； H, 8.24； N, 2.16； S, 9.90. Found (％) : C, 72.41； H, 8.57； N, 2.05； S, 9.62.

For better comparison and elucidation of the structure-property correlations of TRTOR-based polymers P5, BTR (P1) , BTOR (P2) , DTP (P3) , and TTOR-based (P4) polymer analogues were also synthesized. After polymerizations, the polymer chains were end-capped with mono-functionalized thiophene⁶⁸. The polymers were collected by precipitation in methanol, which were then subjected to purification via Soxhlet extractions using different solvent sequences, depending on the polymer solubility. The identity and purity of the product polymers were supported by ¹H NMR as well as by elemental analysis. All the polymers exhibit good solubility in common organic solvents for device fabrication. Polymer molecular weights were measured by gel permeation chromatography (GPC) versus polystyrene standards. Number average molecular weight, M_n, and polydispersity index (PDI) data are summarized in Table 1.

Table 1. Molecular weights, optical absorption, and electrochemical data for polymer series P1-P5

^a GPC versus polystyrene standards, trichlorobenzene as eluent, at 170 ℃. ^b Solution absorption spectra (1×10^-5 M in chloroform) . ^cThin film absorption spectra of pristine film cast from 5 mg/mL CHCl₃ solution. ^d E_HOMO ＝ - (E_ox ^onset + 4.80) eV, and E_ox ^onset determined electrochemically using Fc/Fc⁺ internal standard. ^e E_LUMO ＝E_HOMO + E_g ^opt. ^f Optical bandgap estimated from absorption edge of as-cast thin film.

It is instructive to compare the polymer solubilities. Among all polymers, P1 is most soluble due to its twisted backbone induced by the head-to-head linkage. Due to the single S…O interaction in TRTOR, P5a shows greatly enhanced solubilities versus P2, which has stronger BTOR double S…O interactions⁵⁷. Hence, polymers P5b and P5c with shorter alkyl chains are also synthesized and demonstrate good solubility at 25 ℃, however P2 analogues having the same side chains are intractable. Therefore, enhanced materials processability can be achieved by optimizing the intramolecular S…O interactions. For polymer P4, a large branched 2-hexyldecyl chain is attached to the phthalimide unit for achieving good materials solubility since the TTOR unit only contains one solubilizing side chain.

Polymer Optical and Electrochemical Properties

Absorption spectra of all polymer films are depicted in Figure 2, and the relevant absorption data and optical bandgaps are summarized in Table 1. In solution, all polymers show featureless absorption profiles (Figure 8) , which indicate a lack of aggregation and ordering in chloroform. From solution to film state, the polymers show bathochromic shifts due to the increased backbone planarity and enhanced aggregation⁶⁹. Among all polymers, P2 shows the most bathochromically shifted absorption and the smallest bandgap of 1.65 eV due to the strong BTOR electron-donating ability. In comparison to P1, the insertion of the oxygen atom between the thiophene and alkyl side chain leads to a dramatic red shift (202 nm) of the absorption maximum and a ～0.8 eV smaller optical bandgap for P2 in film state. This substantialbandgap narrowing in P2 is attributed to the stronger alkoxy substituent electron-donating ability (versus that of an alkyl substituent) , more planar polymer backbone due to the reduced steric hindrance by replacing a CH₂ with a less bulky O and the intramolecular non-covalent S…O interaction.

Polymer P3 containing the 5H-dithieno [3, 2-b: 2’ , 3’ -d] pyran (DTP) ⁶² electron donor unit has a bandgap of 1.93 eV, which is between that of P1 (2.42 eV) and P2 (1.65 eV) . In comparison to the bandgap of P2, the larger P3 bandgap (1.93 eV) is attributed to the weaker electron donating ability of DTP which contains one electron donating OR and one CH₂ versus two ORs in BTOR. Considering the comparable electronic properties of DTP and TRTOR (Figure 1) with each having one electron donating OR and one CH₂, P5a exhibits red-shifted absorption and a smaller bandgap (1.85 eV) versus that of P3 (1.93 eV) , likely reflecting the more compact intermolecular stacking due to the absence of out-of-plane substituents and greater phthalimide acceptor-thiophene donor coplanarity in P5a, supported by DFT analysis (Figure 10) . Therefore, TRTOR should be a more effective unit for creating narrow bandgap polymers than DTP.

It is instructive to compare the optical absorption spectra of P4 and P5a, which both contain a single electron-donating alkoxy substituent. In spite of potentially enhanced steric repulsion by introducing the solubilizing alkyl chain on TRTOR vs TTOR, P5a shows a red-shifted absorption maximum and a slightly smaller bandgap than P4. The smaller P5a bandgap is reasonably attributed to the weak electron-donating ability of the alkyl chain, but the effect of polymer molecular weight (M_n) should not be ruled out⁷⁰. Importantly, these results show that the TRTOR alkyl chain is not detrimental to backbone planarity or molecule packing, otherwise the P5a bandgap would be greater than that of P4. Due to the weaker conformational locking strength of the single TRTOR S…O non-covalent interaction vs the double S…O interaction in BTOR, polymers P5b and P5c containing smaller solubilizing groups were also synthesized (Scheme 1) and have good solubility. As the solubilizing substituents become smaller, P5b and P5c have red-shifted absorptions and smaller bandgaps of 1.79 and 1.81 eV, respectively, accompanied by a distinctive absorption shoulder ～640 nm. From the solution to film state, TRTOR polymers P5 show the largest redshift (～100 nm) of the absorption maximum versus others in the series (18-47 nm) , indicating the highest degree of polymer backbone conformational change. Such changes are attributed to the strong TRTOR solubilizing ability, the weak single S…O conformational locking, and the high degree of film state backbone planarity. Of all the present polymers, only those having S…O interactions show optical absorption shoulders typical of ordered film structures^17, 71, 72. From the optical absorption profiles and DFT results it can be concluded that the steric benefit and the S…O interaction of the single alkoxy side chain are effective to lock polymer backbone to achieve planar conformation. Clearly the addition of the extra 3-position bithiophene alkyl substituent is not detrimental to polymer packing in TRTOR-based polymers.

The electrochemical properties of polymers P1-P5 were investigated using cyclic voltammetry with a ferrocene/ferrocium (Fc/Fc⁺) internal standard (Figure 2b) . Among all polymers, P1 doesn’t show an obvious oxidation peak, likely due to the weak BTR electron donor and limited backbone conjugation created by the head-to-head linkage. In contrast, polymers P2-P5 exhibit distinctive oxidation peaks. Going from P1 to P2, the O insertion affords the highest lying HOMO (-4.93 eV) in the series for polymer P2, in good agreement with the DFT computation (Figure 1) , and reflecting the strong BTOR unit electron donor ability. P3 has a low-lying HOMO of -5.34 eV due to the moderate DTP electron donating ability⁶² and torsional polymer backbone^20, 73. In comparison to P3, polymer P4 shows a slightly higher-lying HOMO at -5.28 eV, attributable to the higher degree of P4 conjugation due to more planar backbone and compact packing⁷⁴. In comparison to BTOR-based polymer P2, replacement of one alkoxy substituent by an alkyl substituent lowers the P5a HOMO (-5.19 eV) by 0.26 eV vs that of P2 (-4.93 eV) . Polymer P5c with a branched N-2-ethylhexyl group has a slightly lower HOMO (-5.25 eV) than P5a (-5.19 eV) and P5b (-5.18 eV) with linear N-alkyl substituents⁷⁴. In comparison to P4, polymers P5a-c have slightly higher HOMOs, likely due to the weak electron-donating P5 alkyl substituent. From the electrochemical data, the removal of one oxygen in BTOR effectively lowers the TRTOR polymer HOMOs by a large margin (～ 0.3 eV) , which should enhance I_on/I_off ratios and device stability in OTFTs as well as increase V_ocs in PSCs (vide infra) ^75-77.

Polymer Thermal Properties

Polymer thermal analysis was carried out by differential scanning calorimetry (DSC, Figure 3) . The BTOR-based polymer P2 shows irreversible endotherm around 340 ℃, which is likely attributed to the thermal decomposition of polymer according to the thermogravimetric analysis (Figure 9) ⁵⁷. For the DTP-based polymer P3, DSC reveals a featureless thermogram, indicating amorphous character or low crystallinity, while the TRTOR-based polymers P5a-c show distinct thermal transitions, indicating higher degrees of crystallinity vs BTOR-based polymer P2 and DTP-based polymer P3¹⁷. Therefore, in comparison to BTOR-based polymer P2, the removal of one O is not detrimental to TRTOR-based P5 crystallinity. Compared to DTP-based P3, the DTP ring-opening affords enhanced crystallinity for TRTOR-based polymer P5, attributable to eliminating the out-of-plane alkyl substituents and the TRTOR centrosymmetric geometry. As the solubilizing substituents contract, the transition temperatures become higher and peaks sharpen from P5a→P5b^33, 71. Note also that in spite of its twisted backbone, dialkylbithiophene-based polymer P1 shows a distinct thermal transition at a low temperature of ～200 ℃, consistent with some extent of ordering.

Monomer and Polymer Synthesis-wherein R is a branched alkane

1c: 2-Butyl-1-octylbromide synthesized by following Scheme 24

Bromine (100mmol, 5.115mL) , triphenylphosphine (26.18g, 100 mmol) were dissolved in 250 mL of DCM and the solution was bubbled with Ar for 10 min. 2-butyl-1-octanol (18.635g, 100 mmol) was added at 0 ℃ and stirred at this temperature for 30 min and then at room temperature overnight. Then the reaction was added little Na₂SO₃, After removal of solvent, residue was filtrated and washed with hexane. The crude product was passed through a plug of silica gel using PE as an eluent to give colorless oil (22.0g, 88.1％) .

¹H NMR (400 MHz, CDCl₃) δ 3.45 (d, J ＝ 4.8 Hz, 2H) , 1.59 (dd, J ＝ 11.1, 5.3 Hz, 1H) , 1.40 –1.21 (m, 16H) , 0.90 (q, J ＝ 6.9 Hz, 6H) .

¹³C NMR (125 MHz, CDCl₃) δ 39.88, 39.62, 32.71, 32.40, 31.95, 29.61, 28.92, 26.68, 22.99, 22.80, 14.25, 14.21.

2c: 3- (2-Butyl-1-octyl) thiophene synthesized by following Scheme 25

Magnesium, Turnings (1.147 g, 47.17 mmol) and iodine (76.6 mg, 0.3018 mmol) was dissolved in 50 mL of THF under an Ar atmosphere. 2-Butyl-1-octylbromide (9.496g, 38.1 mmol) in 25 mL was added over 10 min and the mixture was refluxed for 2 h to afford the Grignard reagent. 3-Bromothiophene (4.891g, 30mmol) and NiCl₂ (dppp) (256 mg, 0.4725 mmol) was dissolved in 25 mL of THF and the Grignard reagent was added slowly keeping with the reaction temperature at 0 ℃. The reaction mixture was stirred at room temperature overnight. The reaction was quenched with 2 M of hydrochloric acid (15mL) . DCM was added and the organic layer was washed three times with water. The organic layer was dried over MgSO₄ and the solvent was removed under reduced pressure. The crude product was passed through silica gel using PE as an eluent to give colorless oil (3g, 39.6％) .

¹H NMR (400 MHz, CDCl₃) δ 7.23 (dd, J ＝ 4.9, 3.0 Hz, 1H) , 6.90 (t, J ＝ 4.2 Hz, 2H) , 2.56 (d, J ＝ 6.8 Hz, 2H) , 1.67 –1.58 (m, 1H) , 1.25 (d, J ＝ 3.7 Hz, 19H) , 0.88 (t, J ＝ 6.7 Hz, 7H) .

¹³C NMR (100MHz, CDCl₃) δ 142.07 , 128.96, 124.91 , 120.78 , 39.08 , 37.88 , 34.86 , 33.86 , 33.53 (d, J ＝ 6.0 Hz) , 33.17 , 32.10 (d, J ＝ 7.3 Hz) , 29.92 (d, J ＝ 15.2 Hz) , 29.10 (d, J ＝ 14.2 Hz) , 26.80 (d, J ＝ 9.7 Hz) , 23.27 (d, J ＝ 13.7 Hz) , 22.86 (d, J ＝ 3.2 Hz) , 14.30 (t, J ＝ 3.8 Hz) .

3c: 2-Bromo-3- (Butyl-1-octyl) thiophene synthesized by following Scheme 26

3- (2-Butyl-1-octyl) thiophene (6.0 g, 23.77mmol) and N-bromosuccinimide (4.23g, 23.77mmol) was dissolved in 100 mL of 1: 1 mixture of acetic acid and chloroform and the mixture was stirred at room temperature overnight. Water was added to the reaction and the organic layer was washed with water and saturated sodium bicarbonate aqueous solution, and water. After the removal of solvent with rotary evaporator, the crude passed through a plug of silica gel with PE. The product was afforded colorless oil (6.36g, 81.3％) .

¹H NMR (400 MHz, CDCl₃) δ 7.18 (d, J ＝ 5.6 Hz, 1H) , 6.76 (d, J ＝ 5.6 Hz, 1H) , 2.49 (d, J ＝ 7.2 Hz, 2H) , 1.64 (s, 1H) , 1.26 (dd, J ＝ 10.7, 8.6 Hz, 16H) , 0.88 (t, J ＝ 6.8 Hz, 6H) .

¹³C NMR (100 MHz, CDCl₃) δ 141.19, 128.83, 124.93, 109.42, 38.54, 34.03, 33.35, 33.05, 31.90, 29.68, 28.78, 26.51, 23.05, 22.69, 14.13.

4c: 2- (3- (2-Butyl-1-octyl) thiophene) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane synthesized by following Scheme 27

A solution of bromide 1 (5.0g, 15.09mmol) in THF (35mL) was cooled to -78 ℃, and a 2.4M solution of n-BuLi in hexane (6.92mL, 16.6mmol) . The mixture was stirred for 90min at -78 ℃. 2-isopropoxy-4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane (3.088g, 16.6mmol) was added, the mixture was stirred at -78 ℃ for 30min and allowed to reach room temperature and stirred for 12h, then the mixture was poured into water, extracted several times used diethyl ether, The organic layer was dried over MgSO₄ and the solvent was removed under reduced pressure. The crude product was passed through silica gel using PE: DCM (5: 1) as an eluent to afford the compound 4c (2.58g, 45.2％) .

¹H NMR (400 MHz, CDCl₃) δ 7.47 (d, J ＝ 4.7 Hz, 1H) , 6.97 (d, J ＝ 4.7 Hz, 1H) , 2.81 (d, J ＝ 7.2 Hz, 2H) , 1.58 (s, 1H) , 1.33 (s, 12H) , 1.28 –1.21 (m, 16H) , 0.89 –0.85 (m, 6H) .

¹³C NMR (100 MHz, CDCl₃) δ 153.88, 131.15, 131.10, 83.67, 40.27, 34.94, 33.59, 33.25, 32.08, 29.95, 28.94, 26.70, 24.92, 23.28, 22.86, 14.29.

5c: 3- (2-propylheptan-1-oloxy) thiophene synthesized by following Scheme 28

3-methoxythiophene (3.0 g, 26.28 mmol) , 2-propylheptan-1-ol (4.159g, 26.28mmol) and anhydrous sodium hydrogen sulfate (0.5 g, 4.16 mmol) were charged into around bottom flask. Toluene (100 mL) was then added, purged by argon for 30 min and the mixture was heated to 130 ℃for 19 hr under argon protection. After cooling to room temperature, saturate NaHCO₃ water was added and extraction with ethyl acetate was done. The organic layer was dried over anhydrous MgSO₄, filtered and concentrated for purification via column chromatography (silica gel, PE 100％) to afford compound 5c (3.5g, 55.4％) .

¹H NMR (400 MHz, CDCl₃) δ 7.18 (dd, J ＝ 5.2, 3.1 Hz, 1H) , 6.77 (dd, J ＝ 5.2, 1.5 Hz, 1H) , 6.23 (dd, J ＝ 3.1, 1.5 Hz, 1H) , 3.84 (d, J ＝ 5.7 Hz, 2H) , 1.85 –1.74 (m, 1H) , 1.51 –1.24 (m, 12H) , 0.92 (dt, J ＝ 9.9, 6.9 Hz, 6H) .

¹³C NMR (100 MHz, CDCl₃) δ 158.45, 124.54, 119.78, 96.86, 77.48, 77.16, 76.84, 73.26, 37.93, 33.82, 32.36, 31.44, 26.66, 22.80, 20.15, 14.58, 14.24.

6c: 2-bromo-3- (2-propylheptan-1-oloxy) thiophene synthesized by following Scheme 29

Compound 5c (3.5g, 14.56mmol) was dissolved in anhydrous CHCl₃ (50mL) and cool down to 0 ～ 4 ℃via an ice bath. NBS (2.46 g, 13.85 mmol, ) was then dissolve in anhydrous DMF and added into the solution drop wise via a dropping funnel. The mixture was then stirred for 1 hr with exclusion from light, removed from ice bath and warm up to room temperature. It was then allowed to stirred for overnight with protection from light. water was added and extraction with CHCl₃ was done. The organic layer was dried over anhydrous MgSO₄, filtered and concentrated for purification via column chromatography (silica gel, PE) to afforded the pure compound 6c (3.6g, 77.4％) .

¹H NMR (400 MHz, CDCl₃) δ 7.18 (d, J ＝ 5.9 Hz, 1H) , 6.74 (d, J ＝ 6.0 Hz, 1H) , 3.91 (d, J ＝ 5.8 Hz, 2H) , 1.76 (dd, J ＝ 11.5, 5.8 Hz, 1H) , 1.50 –1.22 (m, 14H) , 0.98 –0.82 (m, 7H) .

¹³C NMR (125 MHz, CDCl₃) δ 154.93, 124.22, 117.63, 91.63, 77.41, 77.16, 76.91, 75.22, 38.09, 33.60, 32.36, 31.25, 26.61, 22.79, 20.12, 14.60, 14.26.

7c: 3- (2-Butyl-1-octyl) -3' - (2-propylheptan-1-oloxy) -2, 2' -bithiophene synthesized by following Scheme 30

To a 150 mL 3-necked reaction flask were added compound 4c (2.58g, 6.818mmol) , 2.72g (8.52mmol) of compound 6c, and 80 mL of toluene. The resulting mixture was stirred and purged with argon before a mixture of 0.474g [Pd (PPh3) 4] , 1.25g of Aliquat in 5 mL toluene, and 12.0mL of 2 M aqueous Na₂CO₃ was added. Subsequently, the reaction mixture was heated at 105 ℃ for 15 h, cooled to room temperature and diluted with DCM. Extracted with DCM, Combined organic phases were washed with water , dried over MgSO₄, and concentrated in vacuum. The crude product was passed through silica gel using PE as an eluent to afforded the compound 7c (1.65g, 49.3％) .

¹H NMR (500 MHz, CDCl₃) δ 7.20 (dd, J ＝ 19.2, 5.4 Hz, 2H) , 6.87 (dd, J ＝ 7.6, 5.4 Hz, 2H) , 3.86 (d, J ＝ 5.6 Hz, 2H) , 2.63 (d, J ＝ 7.2 Hz, 2H) , 1.75 –1.66 (m, 1H) , 1.60 (s, 1H) , 1.44 -1.14 (m, 28H) , 0.94 –0.79 (m, 12H) .

¹³C NMR (125 MHz, CDCl₃) δ 154.02, 140.11, 129.53, 128.40, 124.34, 123.30, 117.71, 113.52, 77.41, 77.16, 76.91, 74.75, 38.90, 38.19, 33.92, 33.62, 33.56, 33.24, 32.37, 32.08, 31.29, 29.85, 28.83, 26.60, 23.20, 22.85, 22.79, 20.06, 14.58, 14.29, 14.27.

8c: 3- (2-Butyl-1-octyl) -3' - (2-propylheptan-1-oloxy) -5, 5’ -bis (trimethylstannyl) 2, 2' -bithiophene synthesized by following Scheme 31

To a flask was added compound 7c (1.3176g, 2.6843mmol) and 15mL dry THF. The resulting clear solution was cooled to -78 ℃ using dry ice/acetone bath. Then 2.684 mL n-BuLi solution in hexane (6.4423 mmol, 2.4 mol/L) was added dropwise. After stirring at -78 ℃ for 1 h and room temperature for 1 h, and then cooled to -78 ℃, 6.98mL trimethyltin chloride (6.98 mmol, 1 mol/L) was added in one portion, and then the cooling bath was removed. After being stirred at ambient temperature for 4 h, the reaction mixture was quenched with water carefully and then poured into cool water and extracted with diethyl ether for twice. After removal of organic solvent, the monomer was obtained as a yellowish oil (1.85 g, 84.5％) .

¹H NMR (400 MHz, CDCl₃) δ 6.90 (d, J ＝ 5.4 Hz, 2H) , 3.89 (d, J ＝ 5.7 Hz, 2H) , 2.68 (d, J ＝ 7.1 Hz, 2H) , 1.77 –1.68 (m, 1H) , 1.64 (s, 1H) , 1.49 –1.38 (m, 2H) , 1.37 –1.12 (m, 26H) , 0.86 (ddd, J ＝ 9.8, 6.1, 4.1 Hz, 12H) , 0.45 –0.26 (m, 36H) .

¹³C NMR (125 MHz, CDCl₃) δ 155.14, 140.42, 138.00, 135.68, 135.24, 134.82, 124.96, 119.88, 77.41, 77.16, 76.91, 74.73, 38.89, 38.28, 33.79, 33.70, 33.61, 33.31, 32.44, 32.10, 31.37, 29.90, 28.85, 26.67, 26.56, 23.24, 22.86, 22.83, 20.12, 14.63, 14.35, 14.31, 14.30, -8.17, -8.19.

5d: 3- (2-Butyl-1-octyloxy) thiophene synthesized by following Scheme 32

This compound was prepared with the same procedure according to 5c.

¹H NMR (400 MHz, CDCl₃) δ 7.17 (dd, J ＝ 5.1, 3.2 Hz, 1H) , 6.80 –6.73 (m, 1H) , 6.22 (dd, J ＝ 3.0, 1.4 Hz, 1H) , 3.83 (d, J ＝ 5.7 Hz, 2H) , 1.81 –1.70 (m, 1H) , 1.41 –1.23 (m, 15H) , 0.95 –0.86 (m, 6H) .

¹³C NMR (125 MHz, CDCl₃) δ 158.46, 124.56, 119.80, 96.88, 77.41, 77.16, 76.91, 73.28, 38.12, 32.01, 31.49, 31.18, 29.83, 29.21, 26.97, 23.21, 22.83, 14.27, 14.25.

6d: 2-bromo-3- (2-Butyl-1-octyloxy) thiophene synthesized by following Scheme 33

This compound was prepared with the same procedure according to 6c.

¹H NMR (400 MHz, CDCl₃) δ 7.18 (d, J ＝ 5.9 Hz, 1H) , 6.73 (d, J ＝ 5.9 Hz, 1H) , 3.90 (d, J ＝ 5.8 Hz, 2H) , 1.78 –1.69 (m, 1H) , 1.51 –1.21 (m, 16H) , 0.88 (t, J ＝6.8 Hz, 6H) .

¹³C NMR (125MHz, CDCl₃) δ 154.94, 124.22, 117.65, 91.63, 75.24, 38.28, 31.99, 31.28, 30.97, 29.82, 29.16, 26.91, 23.20, 22.83, 14.27, 14.25.

7d: 3- (2-Butyl-1-octyl) -3' - (2-Butyl-1-octyloxy) -2, 2' -bithiophene synthesized by following Scheme 34

This compound was prepared with the same procedure according to 7c.

¹H NMR (400 MHz, CDCl₃) δ 7.22 (d, J ＝ 5.2 Hz, 5H) , 7.18 (d, J ＝ 5.6 Hz, 5H) , 6.87 (dd, J ＝ 5.3, 3.9 Hz, 10H) , 3.88 (d, J ＝ 5.6 Hz, 11H) , 2.64 (d, J ＝ 7.2 Hz, 11H) , 1.64 (dd, J ＝ 12.1, 6.0 Hz, 13H) , 1.52 –1.13 (m, 184H) , 0.93 –0.81 (m, 88H) .

¹³C NMR (100MHz, CDCl₃) δ 154.03, 140.11, 129.51, 128.42, 124.35, 123.30, 117.67, 113.48, 39.86, 38.89, 33.96, 33.59, 33.27, 32.07, 30.50, 29.85, 29.17, 28.84, 26.61, 23.85, 23.19, 22.84, 14.27, 14.22, 11.19.

8d: 3- (2-Butyl-1-octyl) -3' - (2-Butyl-1-octyloxy) -5, 5’ -bis (trimethylstannyl) 2, 2' -bith iophene synthesized by following Scheme 35

This compound was prepared with the same procedure according to 8c.

¹H NMR (500 MHz, CDCl₃) δ 6.91 (d, J ＝ 5.8 Hz, 5H) , 3.89 (d, J ＝ 5.1 Hz, 5H) , 2.68 (d, J ＝ 6.8 Hz, 5H) , 1.71 (d, J ＝ 5.5 Hz, 3H) , 1.64 (s, 3H) , 1.43 (d, J ＝ 5.1 Hz, 6H) , 1.35 –1.15 (m, 86H) , 0.94 –0.81 (m, 35H) , 0.45 –0.27 (m, 47H) .

¹³C NMR (101 MHz, CDCl₃) δ 155.16, 140.45, 138.01, 135.71, 135.27, 134.83, 124.99, 119.90, 77.48, 77.16, 76.84, 74.76, 38.91, 38.49, 33.80, 33.63, 33.33, 32.11, 32.06, 31.44, 31.12, 29.90, 29.20, 28.86, 27.00, 26.58, 23.24, 22.86, 14.34, 14.28, -8.18, -8.19.

1d: 2-propylheptan-1-olbromide synthesized by following Scheme 36

This compound was prepared with the same procedure according to 1c.

¹H NMR (400 MHz, CDCl₃) δ 3.44 (d, J ＝ 4.8 Hz, 2H) , 1.60 (dt, J ＝ 11.3, 5.8 Hz, 1H) , 1.41 –1.21 (m, 12H) , 0.95 –0.85 (m, 6H) .

¹³C NMR (101 MHz, CDCl₃) δ 77.48, 77.16, 76.84, 39.73, 39.39, 35.00, 32.64, 32.13, 26.36, 22.75, 19.87, 14.35, 14.19.

2d: 3- (2-propylheptan-1-ol) thiophene synthesized by following Scheme 37

This compound was prepared with the same procedure according to 2c.

¹H NMR (400 MHz, CDCl₃) δ 7.22 (dd, J ＝ 4.9, 3.0 Hz, 1H) , 6.92 –6.87 (m, 2H) , 2.56 (d, J ＝ 6.8 Hz, 2H) , 1.66 –1.58 (m, 1H) , 1.34 –1.17 (m, 20H) , 0.87 (ddd, J ＝ 10.0, 4.9, 2.6 Hz, 9H) .

3d: 2-Bromo-3- (2-propylheptan-1-ol) thiophene synthesized by following Scheme 38

This compound was prepared with the same procedure according to 3c.

¹H NMR (400 MHz, CDCl₃) δ 7.18 (d, J ＝ 5.6 Hz, 1H) , 6.76 (d, J ＝ 5.6 Hz, 1H) , 2.50 (d, J ＝ 7.2 Hz, 2H) , 1.72 –1.62 (m, 1H) , 1.40 –1.16 (m, 20H) , 0.93 –0.84 (m, 9H) .

¹³C NMR (101 MHz, CDCl₃) δ 141.31, 128.96, 125.06, 109.57, 38.52, 35.88, 34.17, 33.45, 32.38, 26.34, 22.82, 19.86, 14.58, 14.26.

4d: 2- (3- (2-propylheptan-1-ol) ) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane synthesized by following Scheme 39

This compound was prepared with the same procedure according to 4c.

¹H NMR (400 MHz, CDCl₃) δ 7.47 (d, J ＝ 4.7 Hz, 1H) , 6.97 (d, J ＝ 4.7 Hz, 1H) , 2.81 (d, J ＝ 7.2 Hz, 2H) , 1.67 –1.58 (m, 1H) , 1.38 –1.16 (m, 24H) , 0.85 (dd, J ＝ 14.9, 7.1 Hz, 6H) .

7e: 3- (2-propylheptan-1-ol) -3' - (2-propylheptan-1-oloxy) -2, 2' -bithiophene synthesized by following Scheme 40

This compound was prepared with the same procedure according to 7c.

¹H NMR (500 MHz, CDCl₃) δ 7.23 (d, J ＝ 5.2 Hz, 1H) , 7.18 (d, J ＝ 5.5 Hz, 1H) , 6.87 (dd, J ＝ 8.9, 5.4 Hz, 2H) , 3.87 (d, J ＝ 5.6 Hz, 2H) , 2.64 (d, J ＝ 7.2 Hz, 2H) , 1.75 –1.68 (m, 1H) , 1.39 (d, J ＝ 6.8 Hz, 2H) , 1.34 –1.11 (m, 23H) , 0.92 –0.80 (m, 12H) .

¹³C NMR (126 MHz, CDCl₃) δ 154.03, 140.08, 129.51, 128.41, 124.34, 123.30, 117.70, 113.52, 77.41, 77.16, 76.91, 74.75, 38.71, 38.20, 35.97, 33.95, 33.63, 33.50, 32.41, 32.37, 31.29, 26.60, 26.27, 22.86, 22.79, 20.07, 19.77, 14.59, 14.58, 14.28, 14.27.

8e: 3- (2-propylheptan-1-ol) -3' - (2-propylheptan-1-oloxy) -5, 5’ -bis (trimethylstannyl) 2, 2' -bithiophene synthesized by following Scheme 41

This compound was prepared with the same procedure according to 8c.

¹H NMR (400 MHz, CDCl₃) δ 6.91 (d, J ＝ 5.8 Hz, 2H) , 3.89 (d, J ＝ 5.7 Hz, 2H) , 2.68 (d, J ＝ 7.1 Hz, 2H) , 1.72 (dd, J ＝ 11.5, 5.8 Hz, 1H) , 1.66 (s, 1H) , 1.42 (dd, J ＝ 11.7, 5.1 Hz, 2H) , 1.37 –1.12 (m, 25H) , 0.92 –0.78 (m, 13H) , 0.47 –0.25 (m, 18H) .

¹³C NMR (126 MHz, CDCl₃) δ 155.15, 140.42, 137.97, 135.70, 135.27, 134.81, 124.96, 119.88, 77.41, 77.16, 76.91, 74.74, 38.68, 38.27, 36.07, 33.83, 33.69, 33.48, 32.44, 31.37, 26.66, 26.20, 22.86, 22.83, 20.11, 19.79, 14.63, 14.32, 14.30, -8.18.

General Procedure for Polymerizations via Stille Coupling for Synthesis of Polymers P1’ -P6’ according to Scheme 42-Scheme 47.

An glass tube was charged with two monomers (0.2 mmol each) , tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) _, and tris (o-tolyl) phosphine (P (o-tolyl) ₃) (1: 8, Pd₂ (dba) ₃: P (o-tolyl) ₃ molar ratio； Pd loading: 0.015equiv) . The tube and its contents were subjected to 3 pump/purge cycles with argon, followed by the addition of anhydrous toluene (4-5 mL) via syringe. The tube was sealed under argon flow and then stirred at 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation. Then, 0.05 mL of 2- (tributylstanny) thiophene was added and the reaction mixture was stirred under microwave irradiation at 140 ℃ for 0.5 h. Finally, 0.10 mL of 2-bromothiophene was added and the reaction mixture was stirred at 140 ℃ for another 0.5 h. After cooling to room temperature, the reaction mixture was slowly dripped into 100 mL of methanol (containing 1 mL 12 N hydrochloric acid) under vigorous stirring. After stirring for 1h, the solid precipitate was transferred to a Soxhlet thimble. After drying, the crude product was subjected to sequential Soxhlet extraction with the choice of solvents and sequence depending on the solubility of the particular polymer. After final extraction, the polymer solution was concentrated to approximately 6 mL, and then dripped into 100 mL of methanol under vigorous stirring. The polymer was collected by filtration and dried under reduced pressure to afford deep colored solid as the product.

Figure 17. shows UV-Vis absorption spectra of polymers P1’ -P6’ in thin films, Figure 18. shows UV-Vis absorption spectra of polymers P1’ -P6’ in chloroform solution (1 ×10^-5 M) . UV-Vis absorption spectra of polymer P1’ -P6’ in thin films are shown in Figure 17, and the UV-Vis absorption spectra of polymer P1’ -P6 in dilute solution (CF) in Figure 18， From solution to film state, the polymers show bathochromic shifts due to the increased backbone planarity and enhanced aggregation. In the film, from the polymer P1’ to P2’ , the UV-Vis absorption spectra show bathochromic shifts due to the F atom influence. From solution to film state, the polymers show bathochromic shifts due to the increased backbone planarity and enhanced aggregation.

Device Fabrication and Characterization

Organic Thin Film Transistor Fabrication and Characterization

Top-gate/bottom-contact (TG/BC) device structure was used to investigate the charge transport property of polymers in organic thin-film transistors (OTFTs) . The Corning XG glass with Au/Ni (15 nm/3 nm thick； Ni is employed as an adhesion layer) source/drain electrodes, which are patterned using a conventional photolithography method, is used as device substrates. Substrates were sequentially cleaned with acetone and 2-propanol in an ultrasonic bath for 10 min each, and dried with N₂ blowing. Polymer semiconductors were dissolved in 1, 2-dichlorobenzene (10 mg/mL) . After without or with UV-O₃ treatment of the cleaned substrates for 20 min, polymer solution was spin-coated at 1500 rpm for 120 sec in N₂-purged glove box. The polymer semiconductor films were then thermally annealed in a N₂-purged glove box at 150, 175, 200, 225, 250, or 275 ℃ for 30 min. As a top-gated polymer dielectric layer, poly (methyl methacrylate) (PMMA) was dissolved in n-butyl acetate (80 mg/mL) and spin-coated at 2000 rpm for 60 sec. Residual solvents were completely removed by thermal baking at 80 ℃ for 60 min at the same glove box. Finally, the aluminum (Al) gate electrodes (～35 nm) were deposited via thermal evaporation method in a high vacuum chamber using a metal shadow mask. The electrical characteristics of the OFET devices were measured using a Keithley 4200-SCS in vacuum (below 10^-2 torr) .

Polymer Solar Cell Fabrication and Characterization

Pre-patterned ITO-coated glass with a sheet resistance of < 10Ω/□ is used as the substrate, which is cleaned by sequential sonication in water containing detergent, deionized water, methanol, isopropanol, and acetone followed by UV/ozone (BZS250GF-TC, HWOTECH, Shenzhen) treatment for 20 min. ZnO precursor was prepared according to the published procedure⁸⁹. The precursor solution was spin-coated (4000 rpm for 30 s) onto the pre-patterned ITO-coated glass. The films were annealed at 200 ℃ for 30 min in air, and then transferred into a N₂ glovebox. The ZnO film thickness is about 30 nm. Except P5c: PC₇₁BM blend (1: 1.6 w/w, 26 mg/mL) , P1: PC₇₁BM, P2: PC₇₁BM, P3: PC₇₁BM, P4: PC₇₁BM, P5a: PC₇₁BM, P5b: PC₇₁BM blends (1: 1.5 w/w, 25 mg/mL) in CB with 3 vol％1, 8-octanedithiol (ODT) were spin-coated on the ZnO interfacial layer (600 rpm for 90s) . Finally, MoO_x (～10 nm) and Ag (～100 nm) were thermally evaporated under a shadow mask (pressure ca. 10^-4 Pa) . The effective area for the devices is 0.16 cm². For device characterization, J-V curves were measured under AM 1.5G light (100 mW/cm²) with a computerized Keithley 2400 source meter (Figure 11 without ODT) . The light intensity is calibrated using an NREL-certified monocrystalline Si diode coupled to a KG3 filter to bring spectral mismatch to unity. Device characterization was performed in the N₂ glovebox using a Xeno-lamp-based solar simulator (Newport, Oriel AM1.5G, 100 mW/cm²) .

GIWAXS Measurements

Grazing incidence wide-angle x-ray scattering (GIWAXS) measurements were performed at Beamline 8-ID-E of the Advanced Photon Source at Argonne National Laboratory. Polymer samples were prepared on Si substrate using identical spin speeds, solvents, concentrations and annealing temperature and times to the relevant OTFT and PSC devices. All spectra were collected in air. The photon energy is 7.35 keV

and data were collected on a Pilatus 1M pixel array detector at a sample-detector distance of 204 mm. Spectra were collected at an incidence angle of 0.2°； the films were exposure for 20 seconds. To account for the gaps in the detector array, two images were taken per sample, one with the detector in the standard position and the other translated 23 mm down to fill the gap, the two images are then merged.

1D line cuts were taken from the 2D scattering spectra in the in-plane and out-of-plane directions using the GIXSGUI software package developed by the beamline scientists. To account for air scatter, the line cuts were background subtracted utilizing an exponential fit. The background-subtracted peaks were fit using the multipeak fit function in igor pro. Scherrer analysis was performed utilizing the method by Smiglies⁹⁰ to account for instrumental broadening and detection limits in the 2d detector. The values presented represent a lower limit for correlation length, as the Scherrer analysis does not account for broadening due to defects in the crystallites.

Characterization results

Top-gate/bottom-contact organic thin-film transistors (OTFTs) with poly (methyl methacrylate) (PMMA) gate dielectrics and gold source/drain electrodes were fabricated to characterize the charge transport properties of phthalimide copolymers P1-P5⁷⁸. Device performance data are compiled in Table 2, Table 3 and representative transfer curves (the drain current, I_d versus gate voltage, V_g) of the P2 and P5 OTFTs are shown in Figure 4.

Table 2. Organic thin-film transistor performance and photovoltaic response properties of polymer semiconductors P1-P5

^a Average performance of ≥5 devices. ^b Device area ＝ 0.16 cm².

Table 3. Bottom-gate/top-contact (BG/TC) OTFT performance of polymers P2 and P5 fabricated under various conditions

Table 4. The photovoltaic performance of the five kinds of devices

The data are the average value calculated from 5 devices at least.

BTR-based polymer P1 is inactive in OTFTs, which is attributed to the very low-lying HOMO (-5.66 eV) , twisted polymer backbone, limited conjugation, and low degree of crystallinity⁷⁹. Under optimized condition, P2 shows a high hole mobility (μ_h) of 1.45 cm²/Vs, which is almost 10x than in bottom-gate/bottom-contact OTFTs (0.17 cm²/Vs) ⁵⁷. The high P2 mobility can be partially ascribed to facile hole injection from the gold electrode to the high-lying HOMO, since the bottom-contact gold electrode has lower work function of ca. -4.5 –-4.7 eV. Versus bottom-gate OTFTs, the performance enhancement in the top-gate OTFTs likely reflects the lower contact resistance due to reduced current crowding effects in staggered contact structures⁸⁰, as well as the excellent active channel -polymer dielectric compatibility without charge-trapping sites, and favorable self-encapsulation by the upper dielectric layer and gate electrode. Nevertheless, despite the substantial P2 μ_h, the TFT performance is plagued by high off-currents (10^-8 -10^-7 A) , hence a small on/off-current ratio I_on/I_off ＝ 10^3-4 in the linear regime at a drain voltage, V_d ＝ -10 V (Figure 4a) due to the high-lying P2 HOMO.

New TRTOR-based polymer P5a has an average μ_h ＝ 0.18 cm²/Vs with small off-currents, 10^-12 –10^-11 A and a high I_on/I_off ＝ 10^5-6 (Table 1) ； the maximum P5a mobility measured is 0.42 cm²/Vs from top-gate/bottom-contact OTFTs. The substantial μ_h is attributed to its high degree of polymer backbone planarity, close π-π stacking distance, and an ordered film morphology. In comparison to the BTOR-based polymer P2, P5a shows a > 1000x smaller off-current (10^-12 –10^-11 A) and ～100x higher I_on/I_off (10^5-6) in the linear region (Figure 4a) , primarily ascribable to the lower-lying P5a HOMO. Due to the enhanced solubility, P5b and P5c containing short alkyl substituents are also sufficiently soluble for OTFT fabrication, and the resulting OTFTs has appreciable μ_hs of 0.043 and 0.030 cm²/Vs, respectively. The enhanced P5a mobility with longer alkyl substituents could be attributed to the smaller π-π stacking and more ordered microstructure derived from the side chain crystallization⁴⁷ as revealed by the grazing incidence wide-angle X-ray scattering (GIWAXS, vide infra) . In comparison to P2, P5a films have lower carrier mobility, which is likely due to the lower-lying HOMO and hence a larger charge injection barrier.

Although extensive film growth optimizations were carried out with DTP-based polymer P3, this material exhibits negligible transistor response, in accord with the out-of-plane alkyl chain orientation, twisted backbone, and amorphous film morphology revealed by the GIWAXS (Figure 4) . Therefore, opening the DTP ring affords greatly enhanced μ_h for the TRTOR-based polymer P5a vs that of DTP-based P2. The TTOR-based polymer P4 also shows negligible OTFT mobility, which agrees with the poor film-forming properties and limited crystallinity revealed by GIWAXS (vide infra) . Therefore, introducing an alkyl chain in the bithiophene 3-position greatly increases the hole mobility of the TRTOR-based polymer P5a vs that of TTOR-based polymer P4 due to the more symmetric structure of TRTOR and more crystalline film morphology of P5a. The OTFT study indicates that TRTOR is a promising building block for high-mobility polymer semiconductors.

Inverted PSCs having a device structure, ITO/ZnO/polymer: PC₇₁BM/MoO₃/Ag were fabricated to investigate the solar cell performance of polymers P1-P5⁸¹, and the current density -voltage (J-V) curves are illustrated in Figure 4c, with relevant performance parameters collected in Table 2. During the device optimizations, it was found that the processing additive, 1, 8-octanedithiol (ODT) (Table 9 without ODT) , greatly improves PSC performance by promoting nanoscale phase separation and bicontinuous interpenetrating network formation (vide infra) ^82, 83. Among all polymers, P1 and P4 show negligible PSC response with PCE ≤ 0.1％ (Table 8) , due to their non-ideal film morphologies, poor film-forming properties, and negligible charge transport capacity. The P2 performance parameters of PCE ＝ 3.38％, J_sc＝11.84 mA/cm², V_oc ＝ 0.45 V, and FF ＝ 63.5％are substantially higher than for previous cell with conventional artchitectures⁵⁹. The performance of P2 cells is mainly limited by the small V_oc, in good agreement with the high-lying HOMO (Figure 2b) , reflecting the electron-rich BTOR character. The DTP-based polymer P3 cells have PCE ＝ 1.46％, J_sc ＝ 2.67 mA/cm², V_oc ＝ 0.95 V, and FF ＝ 57.4％. The large V_oc is ascribed to the twisted polymer backbone⁷³, and the small J_sc to the sub-optimal blend film morphology (vide infra) and the negligible carrier mobility as measured from both OTFT/in-plane (Table 2) and space-charge limited current (SCLC, Table 5) /out-of-plane techniques. Note that TRTOR-based P5a shows a promising PCE of 5.62％with a J_sc ＝ 11.81 mA/cm², V_oc ＝ 0.72 V, and FF ＝ 66％. Due to the weaker intramolecular S…O interaction in TRTOR versus the double S…O interactions in BTOR, more compact solubilizing substituents could be used and the resulting P5b cells have a further enhanced PCE ＝ 6.31％with a J_sc ＝ 12.50 mA/cm², V_oc ＝ 0.71 V, and FF ＝ 71.4％. The J_scs integrated from external quantum efficiency (EQE, Figure 12) vs an AM1.5 reference spectrum are within ±5％of those acquired from the J-V data, showing good internal consistency. During the course of device optimization, high FFs of 70-75％were routinely obtained from P5b PSCs under various fabrication conditions, primarily attributable to the high hole mobility of P5b with ν_h, SCLC ＝ 1.98 × 10^-3 cm²/Vs (Table 5) due to elimination of the out-of-plane side substituents and greater film order/crystallinity^23, 84, while P3 PSCs have a s lower FF (57.4％) , which is partially attributed to its low SCLC mobility (2.93× 10^-5 cm²/Vs) . In comparison to P2, TRTOR-based P5 shows greatly increased PSC performance in V_ocs, EQE, and FFs. Using branched 2-ethylhexyl substituted P5c as the donor, a further increases V_oc to 0.77 V. Therefore, TRTOR is an effective unit for creating semiconducting copolymers with large PSC V_ocs. In comparison to P2, the V_oc enhancement is attributed to the depressed HOMO achieved by replacing one alkoxy with an alkyl substituent, and in comparison to P3, the substantially enhanced J_sc and FF are ascribed to the smaller P5 bandgap, closer packing, and higher mobility. Compared to P4, placing an alkyl chain on the bithiophene 3-position greatly enhances P5 PSC response. The P5 performance is far higher than any phthalimide-based polymer reported to date¹⁰, and demonstrates the potential of TRTOR units for high-performance OTFTs and PSCs.

Table 4 show the device performance of P1’ -P4 and P6’ . The P1’ /PC71BM device showed a promising PCE of 7.86％with a VOC of 0.663V, a JSC of 17.984mA/cm2, and a FF of 66.0％.

It is known that the VOC of PSC is proportional to the difference between the HOMO level of polymer and the LUMO level of PC71BM, therefore，the F atom could lower the polymer LUMO and HOMO, so the polymer P1’ have lower HOMO than P2’ a nd P3’ , and the lower lying HOMO level of P1’ compare with P2’ a nd P3’ .

Table 5. Hole and electron mobility of polymer blends measured in SCLC regime

The hole-only and electron-only devices with a structure of ITO/PEDOT: PSS/polymer: PC₇₁M/MoO₃/Ag and Al/polymer: PC₇₁BM/Ca/Al, respectively, are fabricated with or without using the processing additive, 1, 8-octanedithiol (ODT) .

Film Morphology Characterization and Correlations with Device Performance

Grazing incidence wide-angle X-ray scattering (GIWAXS) was carried out at beamline 8-ID-E of the advanced photon source to examine polymer film microstructure and morphology. The polymer films were prepared neat on octyldecyltrichlorosilane (OTS) -modified Si substrates, blended with PC₇₁BM, and blended with PC₇₁BM processed with 3％ (v/v) ODT as the processing additive on bare Si. 2D images for the blend films processed with ODT are presented in Figure 7 and the 2D images for the neat films and the blend films without using processing additive are shown in the Supporting Information (Figures 13 and 14 ) . In-plane (q_xy) and out-of-plane (q_z) line cuts were taken from all 2D spectra to examine polymer orientation differences in the films. Figure 5 shows the line cuts for the neat polymer films on OTS-modified Si substrate and the line cuts for the blend films are presented in the SI (Figure 15) . The d-spacings and crystalline correlation lengths (CCL) from Scherrer analysis⁸⁵ for polymers P2, P5a, P5b, and P5c are collected in Table 8 with the values for polymers P1, P3, and P4 available in the SI (Table 6 and 7) .

Table 6. d-Spacings and crystalline correlation lengths (calculated via Scherrer analysis) for the different diffractions in P1

All calculated domains are from the face-on orientation.

Table 7. d-Spacings and crystalline correlation lengths of polymers P2 and P4 (calculated via Scherrer analysis)

¹ indicates a preferential face-on domain. ² indicates a preferential edge-on domain.

The neat polymer films exhibit a range of differing preferred orientations and relative crystallinities (Figure 5) . Polymers P2 and P5 featuring intramolecular S…O interaction show similar lamellar and π-π stacking structures, while polymers P1, P3, and P4 appear to have more disparate stacking structures. In spite of the existence of head-to-head linkage, the BTR-based polymer P1 demonstrates in-plane (q_xy) peaks that each would be consistent with a face-on lamellar structure. There are 2 different peaks that could be considered as the (100) peak, coming at d-spacings of 39.6 and

and the third d-spacing of

is likely attributed to the second order (200) diffraction of the first one. It is possible that the existence of multiple interaction distances indicates some sort of twist in the backbone, which causes a variety of different side-chain interaction lengths. P1 also demonstrates a large π-π stacking distance of

(Table 6) , likely due to the twisted polymer backbone. On the basis of the diffraction pattern, the DTP-based polymer P3 is almost completely amorphous with only a broad peak at

and no further intermolecular order, which is attributed to its slightly twisted polymer backbone and the out-of-plane side chain orientation. For the TTOR-base polymer, P4 demonstrates a clear edge-on orientation with a lamellar (100) spacing of

and a π-π stacking distance of

Therefore on the basis of the π-π stacking distance, the use of TTOR leads to more compact packing for P4 versus the BTR-based polymer P1, which could be attributed to the reduced steric hindrance and the planarizing intramolecular S…O interaction.

Table 8. d-Spacing and crystalline correlation lengths (calculated via Scherrer analysis) for the face-on domains in polymers P2, P5a, P5b, and P5c

For the polymers containing intramolecular S…O interaction, P2, P5a, P5b and P5c show a fairly standard lamellar structure with short π-π stacking distances. P2 and P5a have larger (100) d-spacings

versus those

of P5b and P5c, consistent with their longer side chains. The π-π stacking distances derived from (010) diffractions are 3.61, 3.56, 3.59,

for P2, P5a, P5b, and P5c neat films, respectively. Therefore, the replacement of the BTOR with TRTOR leads to comparable or even slightly smaller π-π stacking distance. Therefore in comparison to BTOR, the higher degree of steric hindrance by the replacement of one alkoxy chain with an alkyl chain and the weaker single S…O conformation locking strength in TRTOR is not detrimental to the packing and crystallinity of polymer P5a. As the N-substituents on the phthalimide vary from the straight n-dodecyl chain to the branched 2-ethylhexyl chain, the π-π stacking distance is slightly enlarged by

for P5c, which has also been observed in the BTOR-phthalimide polymers⁵⁷ and the alkylthieno [3, 4-c] pyrrole-4, 6-dione-based polymers. ⁷⁴ The smallest π-π stacking distance of

is likely attributed to the highest P5a mobility among P5 in OTFTs. In comparison to the TTOR-base polymer P4 with a π-π stacking distance of

the TRTOR-base polymer P5a show a much smaller π-π stacking distance of

Therefore the attachment of an alkyl chain on the 3-position in bithiophene improves the polymer film crystallinity and narrows the π-π stacking distance for P5a, which is likely attributed to the more symmetric structure of TRTOR and the elimination of the highly branched alkyl chain on the phthalimide unit. The diffraction patterns show that none of polymers P2, P5a, P5b and P5c demonstrate a clear preference for edge-on or face-on orientation in neat films as they show lamellar (100) and π-π stacking (010) diffractions in both the in-plane (q_xy) and out-of-plane (q_z) directions (Figure 5) . Among the TRTOR-based polymers, P5a shows the largest (010) correlation lengths (5.8 nm； Table 8) , which in combination with its smallest π-π stacking distance

is likely contributed to its highest mobility among the polymers P5a-c.

For the P1-5 blend films, the films processed with ODT typically result in more crystalline morphology, which leads to enhanced charge carrier mobility measured in SCLC regime (Table 5) and improved device performance in PSCs. On the basis of the GIWAXS images of the polymer blend, the P1: PC₇₁BM film processed from ODT shows little difference from its neat film or blend counterpart without using processing additive, continuing to demonstrate the multiple lamellar interactions, a likely result of twisted backbone due to the head-to-head linkage containing BTR. P3 continues to demonstrate little intermolecular order, as it shows no scattering beyond an initial isotropic lamellar peak and the PC₇₁BM ring. The total lack of π-π stacking and general amorphous character is an unsurprising result given the out-of-plane side chains that will disrupt polymer stacking, which results in low PCE (1.46％) in PSCs.

P4 demonstrates a high degree of crystalline structure when processed with ODT as evidenced by the sharp and intense on axis diffraction peaks and additional off axis diffraction peaks (Figure 6 and 9) . The poor PSC performance is likely attributed to the overly high crystallinity, which can create poorly intermixed domains and grain boundaries that will cause charge recombination, this is also evident by the large crystallites in the TEM and the relatively low mobility (10^-5 cm²/Vs) as measured in the SCLC regime from the P4: PC₇₁BM film. The blend films of polymers P2, P5a, P5b, P5c featuring intramolecular S…O interaction processed with ODT all demonstrate preferential face-on orientation with high degree of materials crystallinity (Figure 6) , which should be beneficial to charge carrier transport (10^-4 -10^-3 cm²/Vs, Table 5) and extraction in PSCs. ^8, 86 Such morphology in combination with their absorption characteristics leads to the substantial PSC performance in the series.

Table 9. Inverted polymer solar cell performance metrics for polymers P1-P5

Polymer	Polymer: PC₇₁BM	J_sc (mA/cm²)	V_oc (V)	FF (％)	PCE (％)
P1	1: 1.5	NA	NA	NA	NA
P2	1: 1.5	4.15	0.49	49.7	1.01
P3	1: 1.5	2.48	0.94	48.6	1.13
P4	1: 1.5	0.49	0.29	27.5	0.04
P5a	1: 1.5	8.50	0.70	64.5	3.84
P5b	1: 1.5	7.28	0.77	54.0	2.94
P5c	1: 1.6	3.61	0.83	37.3	1.12

The cells have a structure of ITO/ZnO/polymer: PC₇₁M/MoO₃/Al and are fabricated without using processing additive, 1, 8-octanedithiol.

The high planarity of the TRTOR unit enabled by the inclusion of the alkoxy side chains allows for very strong face-on (010) orientation. Due to the reduced side chain bulk breaking up domains on P5b, Scherrer analysis reveals larger face-on (010) domains in P5b than P5a, P5c, and P2 in both blends with and without ODT. This extended π-π periodicity helps explain the increased FF and J_sc in P5b leading to its peak PSC performance in this polymer series.

Overall, the BTOR and TRTOR polymers containing the planarizing alkyoxy side chain demonstrate a much greater affinity for face-on π-π stacking than other polymers in the series. This is consistent with their increased planarity demonstrated throughout and is clearly beneficial for the function of the polymers in PSCs. In spite of comparable charge carrier mobility, blend film crystallinity, and backbone orientation, the BTOR-based polymer P2 shows smaller external quantum efficiency (EQE, Figure 12) and FF (Table 2) versus P5-based PSC, which is likely attributed to the slightly coarser nanoscale phase separation of P2: PC₇₁BM blend as revealed by the transmission electron microscope measurement.

Therefore, the replacement of one alkoxy chain with an alkyl chain can result in a better mixing between the polymer donors P5 and the acceptor PC₇₁BM. The higher J_sc and FF in combination of the much larger V_oc lead to the substantial higher PCE (6.31％) for P5b PSCs versus that (3.38％) of P2 cells. In comparison to TTOR-based polymer, the introduction of alkyl chain on the 3-position of bithiophene in TRTOR leads to crystalline packing more favorable to device performance with a standard lamellar and close π-π stacking morphology and favorable polymer orientation for TRTOR-based polymers. In comparison to the DTP-based polymers, the TRTOR-based polymers show greatly improved J_sc, FF, and PCE due to their more planar backbone, higher degree of crystallinity with favorable backbone orientation, and higher charge carrier mobility.

Transmission electron microscope (TEM) was also used to investigate the blend film morphology of PSCs. For the blend film processed without using additive ODT, the TEM images (Figure 7) show that the PC₇₁BM-rich domains with sizes (up to several hundred nanometers) greater than the typical exciton diffusion length (～20 nm) are embedded in the blend film, which leads to the poor device performance due to the inefficient exciton dissociation. In marked contrast, the use of ODT as the processing additive greatly improved the mixing between the polymer donor and the fullerene acceptor, and nanoscale phase separation with significantly smaller domain sizes as well as a bicontinuous interpenetrating network are clearly visible, which leads to improved PSC performance. The TEM images show that the TRTOR-based P5 blends (Figure 7l-n) have finer domain sizes versus the BTOR-based P2 blend (Figure 7i) , which results in the greater EQEs and FFs for P5 PSC. The better mixing between P5 and PC₇₁BM is likely attributed to the reduced aggregation of P5 due to the weaker single S…O conformation locking strength in TRTOR. Atomic force microscopy (AFM) topographic images (Figure 16) reveal similar morphology evolution after the use of the ODT processing additive.

Figure 19 shows J-V curves of the photovoltaic devices based on the five polymers P1’ -P6’ with PC₇₁BM. P1’ s hows the optimized device performance and the polymer for comparison. The photovoltaic performance of corresponding device is listed in table 4. In contrast, the device based on P1’ exhibited a significantly improved PCE of 7.86％with a J_SC of 17.984mA cm^-2, a V_oc of 0.663V, and a FF of 66.0％. From the polymer P1’ to P3’ , the Voc is decreased from 0.663 to 0.533V, and through change the dialkyl side chain, the Voc have a small change, the dialkyl side chain is long, and then the Voc is increase, because the long dialkyl side chain have steric hindrance, so the HOMO is low, and follow with high Voc.

In summary, we designed and synthesized a novel electron donor unit TRTOR, which contains a head-to-head linkage and hence possesses good solubilizing capability. TRTOR shows well-tailored opto-electrical property and high degree of backbone planarity enabled by the use of a single alkoxy side chain, which reduces side chain steric bulk near the backbone (versus dialkyl bithiophene in BTR) and leads to an optimized single intramolecular S…O interaction. In comparison to the dialkoxy bithiophene BTOR, the replacement of one alkoxy chain with a less electron donating alkyl chain results in lower-lying HOMO for the TRTOR polymers, and such structure modification also improves materials processability without sacrificing backbone planarity and materials crystallinity.

From another perspective, as ring opened DTP, TRTOR has comparable electrical properties but with easy materials accessbility, centrosymmetric geometry, and more compact structure than DTP, which is axisymmetric and contains out-of-plane sidechains. The incorporation of the single alkoxy side chain and optimizing the S…O interaction affords the resulting TRTOR polymers with low-lying HOMO, close intermolecular π-π stacking, high degree of crystallinity, and enhanced materials processability.

When incorporated into organic thin-film transistors and polymer solar cells, the TRTOR-based polymers show highly promising device performance, and the PSC of TRTOR-phthalimide polymer is the highest among all phthalimide-based polymers reported to date. The results demonstrate that TRTOR is an effective building block for constructing high-performance polymer semiconductors, and unitizing alkoxy side chain with reduced steric hindrance and optimizing intramolecular non-covalent S…O interaction is a highly promising strategy for materials design in organic electronics.

Embodiments of the invention have been described above and, obviously, modifications and alterations will occur to others upon the reading and understanding of this specification. The invention and any claims are intended to include all modifications and alterations insofar as they come within the scope of the claims or the equivalent thereof.

Claims

An electron-donating unit of the Formula I,

wherein R¹ is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R² is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms.
A copolymer of the electron-donating unit of claim 1 having the Formula 4,

wherein R¹ is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R² is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms, R¹ and R² are same or different, π is an electron-deficient group, n is 5-80.
The copolymer according to claim 2, characterized in that, π is selected from the following group:

wherein R is a straight or branched alkyl, preferably having 5-15 carbon atoms, and more preferably having 7-12 carbon atoms.
Preparation method of the electron-donating unit of claim 1 wherein R¹ and R² are straight alkyls comprising:

(1) adding 2-bromo-3-alkoxy-thiophene, an alkali carbonateθan organic solvent and water into a reaction vessel, and purging the mixture with an inert gas；

(2) adding Pd (PPh₃) ₄ and then purging an inert gas, heating the mixture to 40-90 ℃；

(3) adding 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane to the mixture and refluxing the mixture at 40-90 ℃；

(4) extracting the reaction mixture and washing；

(5) concentrating the organic layer and purifying to give the electron-donating unit； wherein the alkoxy and alkyl both are straight.
The preparation method according to claim 4, characterized in that, in step (1) , the mole ratio of the 2-bromo-3-alkoxy-thiophene to the alkali carbonate is 1: 0.5-2, preferably 1: 0.7-1.5, more preferably 1: 1；

preferably, the ratio of the organic solvent or water to the 2-bromo-3-alkoxy-thiophene is 2-10 mL/mmol, preferably 3-7 mL/mmol；

preferably, the alkali carbonate is selected from K₂CO₃, Na₂CO₃, Li₂CO₃ or a mixture of at least two of them；

preferably, the organic solvent is selected from THF, EtOH, dioxane, DMF, toluene or a mixture of at least two of them；

preferably, time of the purging is more than 10 minutes, preferably more than 20 minutes, more preferably 30 minutes；

preferably, the mixture is heated to 50-80 ℃； preferably to 70 ℃；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them；

preferably, in step (2) , the mole ratio of the Pd (PPh₃) ₄ to the 2-bromo-3-alkoxy-thiophene is 1: 5-20, preferably 1: 8-15, more preferably 1: 10；

preferably, time of the purging is more than 5 minutes, preferably more than 10 minutes, more preferably 20 minutes；

preferably, the mixture is heated to 50-80 ℃； preferably to 70 ℃；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them；

preferably, in step (3) , the 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is added with a mole ratio to the 2-bromo-3-alkoxy-thiophene of 1: 3-15, preferably 1: 5-10, more preferably 1: 6.3；

preferably, the 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is added dropwise；

preferably, the mixture is refluxed at 50-80 ℃； preferably at 70 ℃；

preferably, in step (4) , the reaction mixture is extracted with organic solvent, preferably with DCM；

preferably, the washing is conducted with water and brine；

preferably, in step (5) , the concentrating is conducted under reduced pressure；

preferably, the purifying is conducted by column chromatography using petroleum ether as an eluent.
Preparation method of the electron-donating unit of claim 1 wherein R¹ or/and R² is (are) branched alkyl comprising:

(1) adding 2-bromo-3-alkoxy-thiophene, 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane and a solvent into a reaction vessel, and purging the mixture with an inert gas； the solvent is known in the art, such as benzene, toluene and the like, or a mixture of at least two of them；

(2) adding a mixture of [Pd (PPh₃) ₄] , Aliquat, and aqueous alkali carbonate, heating the mixture to 90-150 ℃ for 5-30 h；

(3) cooling the reaction mixture to room temperature,

(4) extracting the reaction mixture and washing the combined organic phases after being extracted and drying the organic phase to mainly remove the water therein；

(5) concentrating the organic layer and purifying to give the electron-donating unit； wherein the alkoxy and alkyl both are branched.
The preparation method of according to claim 6, characterized in that, in step (1) , the mole ratio of the 2-bromo-3-alkoxy-thiophene to 2- (3-alkylthiophen-2-yl) -4, 4, 5, 5-tetramethyl-1, 3, 2-dioxaborolane is 1: 0.5-1, preferably 1: 0.7-0.9, more preferably 1: 0.8；

preferably, the mixture is stirred and purged with an inert gas；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them；

preferably, the ratio of the solvent to the 2-bromo-3-alkoxy-thiophene is 10-80 mL/g, preferably 20-50 mL/g；

preferably, in step (2) , the mixture is heated to 100-120 ℃ for 10-20 h, more preferably the mixture is heated to 100-110 ℃ for 13-18 h；

preferably, the Aliquat is in toluene；

preferably, the alkali carbonate is selected from K₂CO₃, Na₂CO₃, Li₂CO₃ or a mixture of at least two of them；

preferably, the mass ratio of [Pd (PPh₃) ₄] , Aliquat, and alkali carbonate is 1: 1-5: 2-10, preferably 1: 2-3: 3-8, more preferably 1: 2.5: 5；

preferably, in step (4) , the reaction mixture is extracted with organic solvent, preferably with DCM；

preferably, the washing is conducted with water；

preferably, the drying is conducted over MgSO₄；

preferably, in step (5) , the concentrating is conducted under reduced pressure；

preferably, the purifying is conducted by column chromatography or silica gel using petroleum ether as an eluent.
Preparation method of the copolymer of claim 2 or 3 comprising:

(1) adding the electron-donating unit of claim 1, an electron-deficient material, tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) , and tris (o-tolyl) phosphine (P (o-tolyl) ₃) into a reaction vessel, and subjecting the reaction vessel and the mixture to an inert gas；

(2) adding an organic solvent； sealing the reaction vessel under an inert gas flow and then stirring while heating；

(3) adding 2- (tributylstanny) thiophene and stirring the reaction mixture while heating； finally, adding 2-bromothiophene and stirring the reaction mixture while heating；

(4) after cooling to room temperature, dripping the reaction mixture into methanol containing hydrochloric acid；

(5) drying the solid precipitate obtained in step (4) to give the crude product, and then extracting the crude product；

(6) after final extraction, concentrating the polymer solution, and then being dripped into methanol, collecting the polymer and drying to give the copolymer.
The preparation method of according to claim 8, characterized in that, in step (1) , the electron-deficient material is selected from the following group:

preferably, the mole ratio of the electron-donating unit of claim 1 to the electron-deficient material is 1: 0.5-2, preferably 1: 0.8-1.5, more preferably 1: 1；

preferably, the mole ratio of the tris (dibenzylideneacetone) dipalladium (0) (Pd₂ (dba) ₃) to tris (o-tolyl) phosphine (P (o-tolyl) ₃) is 1: 4-15, preferably 1: 6-10, more preferably 1: 8； the Pd loading is 0.005-0.1 equiv, preferably 0.01-0.06；

preferably, the reaction vessel and the mixture are subjected to 1-5 pump/purge cycles with Ar；

preferably, the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them；

preferably, in step (2) , the inert gas is selected from any one of Ar, N₂, He, Ne, or a mixture of at least two of them；

preferably, the organic solvent is selected from any one of anhydrous toluene, benzene, chlorobenzene, DMF, or a mixture of at least two of them；

preferably, the ratio of the organic solvent to the electron-donating unit is 10-75 mL/mmol, preferably 5-50 mL/mmol；

preferably, the heating is conducted at 50-170 ℃ for 1-72h, preferably at 80-150 ℃for 3-50h；

preferably, the heating is conducted under microwave irradiation；

preferably, the heating is conducted by 80 ℃ for 10 minutes, 100 ℃ for 10 minutes, and 140 ℃ for 3 h under microwave irradiation；

preferably, in step (3) , the heating is conducted at 80-170 ℃ for more than 0.2 h, preferably at 100-160 ℃ for more than 0.4 h；

preferably, the heating is conducted under microwave irradiation；

preferably, the heating is conducted under microwave irradiation at 140 ℃ for 0.5 h； finally, adding 2-bromothiophene and stirring the reaction mixture at 140 ℃ for another 0.5 h；

preferably, the mole ratio of the 2- (tributylstanny) thiophene to the electron-donating unit is 0.1-0.5: 1, preferably 0.2: 0.4-1；

preferably, the mole ratio of the 2-bromothiophene to the electron-donating unit is 0.2-1.5: 1, preferably 0.4: 0.8-1； preferably, in step (4) , the methanol contains 0.5-10mL hydrochloric acid， preferably 0.5-10mLof 5-20 mol/L hydrochloric acid； preferably, the dripping is conducted under vigorous stirring, preferably is conducted for at least 0.5 h, preferably at least 1 h；

preferably, in step (6) , the dripping is conducted under vigorous stirring；

preferably, the collecting is conducted by filtration；

preferably, the drying is conducted under reduced pressure.
Use of the copolymer according to claim 2 or 3 in thin-film transistor or polymer solar cell.