GB2550145A

GB2550145A - Phase separation for enhanced carrier mobility in OTFT devices

Info

Publication number: GB2550145A
Application number: GB1608144.0A
Authority: GB
Inventors: Wilson Richard; Morey James
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2016-05-10
Filing date: 2016-05-10
Publication date: 2017-11-15
Also published as: GB201608144D0; WO2017194917A1

Abstract

A blend of small molecule organic semiconductor (may be a thiophene-based derivative of linear/branched alkyl groups) and fluorinated polymer (may be a conjugated polymer) is used to form a thin film 7, having an organic semiconductor phase 7b and a fluoropolymer phase 7a, by vertical phase separation during manufacture of a bottom gate organic thin film transistor (OTFT). The phase separated thin film 7 is formed over at least a channel region 6 of the OTFT. The organic semiconductor phase 7b may be in contact with the channel region 6, and the fluoropolymer phase 7a in contact with the environment. The fluoroplymer phase 7a may have low surface energy and high hydrophobicity, such that the OTFT may be operated in aqueous environments, for example in sensors such as biosensors. Monolayers, such as alkyl or aryl silanes, may be formed on the gate dielectric; or thiols on the source/drain electrodes.

Description

PHASE SEPARATION FOR ENHANCED CARRIER MOBILITY IN OTFT DEVICES FIELD OF INVENTION

[0001] This invention relates to organic thin-film transistors (OTFTs), wherein charge carrier mobility is improved by effecting vertical phase separation to form a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase. In further aspects, the present invention relates to a method of manufacturing the aforementioned OTFTs and to biosensors comprising the same.

BACKGROUND OF THE INVENTION

[0002] Organic thin-film transistors (OTFTs) have received considerable attention in recent decades due to their potential to be manufactured on both rigid and flexible substrates at low costs (e.g. by solution processing at low temperatures) and their ease of fabrication. In view of these advantages, OTFTs are an excellent alternative for use in sensing applications, where there is a demand on inexpensive, disposable devices that provide accurate measurements. Taking further into account that the organic materials in OTFTs generally show good compatibility with selective biological recognition elements, biosensor applications are of particular interest.

[0003] A vast number OTFT-based sensor device architectures employ a configuration, wherein an organic semiconductor with a high carrier mobility is deposited close to the gate/channel area, and which further require a top coat layer of a polymer for device encapsulation and to allow attachment of a sensing element for ions or biomolecules, for example. When operating in aqueous environments, it is in many cases desired that the surface exposed to the sensing environment exhibits a low surface energy and high hydrophobicity. While it is known that heavily fluorinated polymer materials may generally meet these requirements, their implementation into such device architectures is often problematic as the fluorous domains do not interact favourably with dissimilar non-fluorinated materials.

[0004] Moreover, efforts have been made in the recent years to further simplify the manufacture process of OTFTs and to ideally reduce the required amounts of organic semiconductor. To this end, vertical phase separation has been explored as a route to fabricate dual layers in OTFT in a single step, wherein a mixed phase consisting of a blend of specific organic semiconductors and insulator polymers in a solvent form two individual phases upon solvent evaporation during manufacturing (see e.g. W. H. Lee, Y. D. Park, Polymers 2014, 6, 1057-1073, or US 8,828,793 B2). As examples of such blends promoting vertical phase separation, blends of thiophene-based polymers (e.g. P3HT) and polymethylmethacrylate (PMMA) used for the formation of phase-separated organic semiconductor and insulating layers may be mentioned (see e. g. A. Arias et al. Adv. Mater. 2006, 19, 2900). However, finding and implementing phase-separated systems is challenging since many blend materials tend to result in non-uniform phase distribution and abrupt phase boundaries, which deteriorates charge transport.

[0005] In view of the above, it remains desirable to provide OTFTs, wherein the surface exposed to the sensing environment has a low surface energy and high hydrophobicity, which exhibit excellent charge carrier mobility and a simple structure, and which may be produced cost-efficiently and in few steps.

SUMMARY OF THE INVENTION

[0006] The present invention solves these problems by effecting vertical phase separation in a blend comprising an organic semiconductor and fluorinated polymer having a low surface energy and thereby simultaneously depositing organic semiconductor material a top coat layer polymer having favourable hydrophobicity, which allows to produce an organic thin film transistor (OTFT) with excellent carrier mobility.

[0007] Generally speaking, the present invention relates to an organic thin film transistor (OTFT) comprising: a substrate; a gate electrode formed on the substrate; a gate dielectric on the gate electrode; source and drain electrodes over the gate dielectric with a channel region therebetween; and a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase over at least the channel region formed by vertical phase separation from a blend comprising a small-molecule organic semiconductor and a fluorinated polymer. The fluoropolymer is preferably a semiconducting fluorinated polymer.

[0008] In further aspects, the present invention relates to methods of manufacturing of said organic thin film transistor (OTFT), and to sensing devices (such as e.g. biosensors) comprising the same.

[0009] In addition, the present invention relates to the use of a blend solution comprising a small-molecule organic semiconductor and a fluorinated polymer to promote vertical phase separation during manufacture of an organic thin film transistor (OTFT).

[0010] Preferred embodiments of the organic thin film transistor (OTFT) according to the present invention, other aspects of the invention, and advantages thereof are described in the following description and the claims. Further benefits will become apparent to the skilled artisan upon consideration of the invention disclosure.

BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 schematically illustrates the general architecture of an exemplary bottom-gate OTFT according to the present invention.

[0012] FIG. 2 schematically shows the configuration of the bottom-gate OTFT as used in the examples of the invention.

[0013] FIG. 3 shows the transfer characteristics of OTFTs using a non-fluorinated host polymer.

[0014] FIG. 4 shows the transfer characteristics of OTFTs using a fluorinated host polymer according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Organic thin film transistor (OTFT) [0015] In one embodiment, the present invention relates to the use of a blend solution comprising a small-molecule organic semiconductor and a fluorinated polymer to promote vertical phase separation during the manufacture of a bottom-gate organic thin film transistor (OTFT).

[0016] The term “vertical phase separation” as used herein, describes the phenomenon that a blend comprising at least two different materials, usually in a solvent, changes from one mixed phase to two individual phases during processing (e.g. evaporation of solvent), so that the resulting separated phases are parallel to the surface of the substrate on which the blend is deposited. It is to be noted that in phase-separated thin film, regions may be present at the interface between the phases wherein both phases coexist, e.g. a region with a phase gradient morphology.

[0017] Advantageously, it has been found that organic thin film transistors (OTFTs) prepared accordingly not only allow the provision of two distinct phases in one single step and thereby simplify their manufacturing process, but that their charge carrier mobility may also be surprisingly enhanced. Moreover, the use according to the present invention enables to provide the combination of an organic semiconductor layer and a polymer layer having low surface energy in a simple manner. Further details on the use according to the present invention will be described below with respect to the embodiments related to the organic thin film transistor (OTFT) and its manufacturing methods.

[0018] One embodiment of an organic thin film transistor (OTFT) according to the present invention comprises: a substrate; a gate electrode formed on the substrate; a gate dielectric on the gate electrode; source and drain electrodes over the gate dielectric with a channel region therebetween; and a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase over at least the channel region formed by vertical phase separation from a blend comprising a small-molecule organic semiconductor and a fluorinated polymer.

[0019] Thus, the organic thin film transistor (OTFT) exhibits a bottom-gate configuration, an example of which is shown in Fig. 1. The structure comprises a gate electrode (2) deposited on a substrate (1) with a gate dielectric/insulating layer (3) provided thereover. Source and drain electrodes (4) and (5) are deposited on the gate dielectric (3) and spaced apart from each other to form a channel region (6) therebetween over the gate electrode (2). A phase-separated thin film (7) comprising a fluoropolymer phase (7a) and an organic semiconductor phase (7b) is provided over at least the channel region (6) and may extend over a portion of the source and drain electrodes (4) and (5), with the organic semiconductor phase (7b) being preferably provided in contact therewith. The fluoropolymer phase (7a) may serve as the polymer top coat layer at the air interface. Thereby, a surface layer with low surface energy is provided, which is particularly advantageous when the layer is exposed to an aqueous environment (e.g. in sensor applications). Alternatively, additional layers may be provided on top of the fluoropolymer phase (7a) or the phase may be modified by attaching sensing elements (e.g. ions, specific biomolecules) on its upper surface.

[0020] Preferably, the OTFT according to the present invention is a single-gate OTFT, as opposed to double-gate OTFTs.

[0021] In a preferred embodiment from the viewpoint of efficient vertical phase separation, the surface energy of the fluorinated polymer is lower than that of the small-molecule organic semiconductor. The surface energy may be quantified (in mN-rrv1) by conventional methods known in the art, e.g. by measuring the contact angle of a drop of liquid placed on the surface of the inspected object and calculating the surface energy from the contact angle based on Young’s equation.

[0022] The fluorinated polymer has preferably a fluorine content of at least 10 wt.-%, more preferably at least 20 wt.-%, especially preferably at least 30 wt.-%, based on the total weight of the fluorinated polymer.

[0023] In another preferred embodiment, the fluorinated polymer is a conjugated polymer, which may contribute to the charge transport within the OTFT. In a further preferred embodiment, the fluorinated polymer is a conjugated polymer comprising alternating single and double bonds or aromatic units along the polymer chain and pendant fluorinated side groups. While not being limited thereto, polymers comprising fluorenyl repeating units according to General Formula (I) may be mentioned as examples:

(l)

Herein, R’, R”, R’” and R”” independently represent a substituted or unsubstituted C1-C50 alkyl group, a substituted or unsubstituted Ce-Ceo aryl group or a substituted or unsubstituted Οβ-Οβο heteroaryl group; n and m are independently 0 to 3; and at least one of R’, R”, R’” and R”” - preferably R’ or R” or both R’ and R” - represents a fluorinated alkyl group or comprises the same as a substituent. The fluorinated alkyl group may have the formulae F2HC-(CF2)p-,F3C-(CF2)p-, or H3C-(CF2)p-, with p being 2 to 30, in embodiments 3 to 15.

[0024] The fluorinated polymer may be exclusively derived from fluorinated monomers or may be a co-polymer formed from a single or multiple different fluorinated monomers and a single or multiple different non-fluorinated monomers. If the fluorinated polymer is a copolymer comprising fluorinated and non-fluorinated repeating units, it is preferable that the content of fluorinated repeating units is 10 to 99 mol-%, more preferably 25 to 99 mol%, further preferably 35 to 99 mol-%, based on the total content of repeating units.

[0025] The small-molecule organic semiconductor may be appropriately chosen by the skilled artisan from known materials, including soluble derivatives of acenes such as tetracene, chrysene, pentacene, pyrene, perylene, coronene, benzodithiophene, anthradithiophene, and other condensed aromatic and hetero-aromatic hydrocarbons; and soluble, suitably substituted, aniline-, thiophene-, pyrrole-, furan-, or pyridine-based oligomers. A review of useful small-molecule organic semiconductors is provided by Usta, H. and Facchetti, A. (2015) Polymeric and Small-Molecule Semiconductors for Organic Field-Effect Transistors, in Large Area and Flexible Electronics (Eds.: M. Caironi and Y.-Y. Noh), Wiley-VCH, Weinheim, Germany, pp. 1-100. In a preferred embodiment, the small-molecule organic semiconductor is a heteroacene derivative, preferably a thiophene-based derivative comprising linear or branched C3-C30 alkyl groups, preferably linear C3-C30 alkyl groups.

[0026] The substrate may generally be rigid or flexible, the substrate material being usually selected from glass, silicon, and plastics (such as poly(ethylene terephthalate) (PET), poly(ethylene-naphthalate) (PEN), polycarbonate and polyimide, for example).

[0027] The source and drain electrodes may be made of materials suitably selected by the skilled artisan. For example, for a p-channel OTFT, preferably the source and drain electrodes comprise a high workfunction material, preferably a metal, with a workfunction of greater than 3.5 eV, for example gold, platinum, palladium, molybdenum, tungsten, or chromium. More preferably, the metal has a workfunction in the range of from 4.5 to 5.5 eV. Metal alloys and oxides (e.g. molybdenum trioxide and indium tin oxide) may also be used. Alternatively, conductive polymers may be deposited as the source and drain electrodes. As example of such a conductive polymer, polyethylene dioxythiophene) (PEDOT) may be mentioned. In an n-channel OTFT, the source and drain electrodes preferably comprise either a metal having a workfunction of less than 3.5 eV such as calcium or barium or a thin layer of metal compound, in particular an oxide or fluoride of an alkali or alkali earth metal for example lithium fluoride, barium fluoride and barium oxide, or conductive polymers. While the source and drain electrodes may be preferably formed from the same material for ease of manufacture, it is also possible that the source and drain electrodes may be formed of different materials for optimization of charge injection and extraction respectively.

[0028] The length of the channel defined between the source and drain electrodes may be up to 800 pm, but preferably the length is less than 500 pm.

[0029] A wide range of conducting materials may be used for the preparation of the gate electrode, e.g. metals (e.g. aluminum or gold) or metal compounds (e.g. indium tin oxide). Alternatively, conductive polymers may be deposited as the gate electrode.

[0030] The thicknesses of the gate electrode, source and drain electrodes may be in the region of 1 to 250 nm, preferably from 2 to 100 nm, as measured by Atomic Force Microscopy (AFM), for example.

[0031] The gate dielectric may be formed by depositing dielectric material which may be suitably selected by the skilled artisan. Organic or inorganic electrically insulating material may be used as gate dielectric material, with polymeric material (polyvinylidenefluoride (PVDF), cyanocelluloses, polyimides, epoxies, etc.) and strontiates, tantalates, titanates, zirconates, aluminum oxides, silicon oxides, tantalum oxides, titanium oxides, silicon nitrides, barium titanate, barium strontium titanate, barium zirconate titanate, zinc selenide, and zinc sulfide being mentioned as examples. In addition, alloys, combinations, and multilayers of these can be used for the gate dielectric. Of these materials, aluminum oxides, silicon oxides, silicon nitrides, and zinc selenide are preferred. The gate dielectric can be deposited in the OTFT as a separate layer, or alternatively, if the gate electrode is made of a oxidizable metal (e.g. Al), the gate dielectric layer may be formed on the gate electrode by oxidation of the metal surface to the respective metal oxide (e.g. AI2O3), e.g. via O2 plasma processes.

[0032] In a preferred embodiment of the present invention, a self-assembled monolayer or other surface treatment is applied on the gate dielectric at the channel region to improve the charge carrier mobility and the on/off ratio of the OTFT, to promote crystallinity, to reduce contact resistance, to repair surface characteristics and to promote adhesion where required.

[0033] Preferably, a first self-assembled monolayer is deposited on the gate dielectric on at least part of the surface of the channel region on which the phase-separated thin film is formed. Advantageously, the self-assembled monolayer decreases the surface energy of the substrate onto which the organic semiconductor is deposited. The surface may be altered from hydrophilic to hydrophobic. In general, by lowering the surface energy of the substrate, the organic semiconductor can form an organized or patterned structure (e.g. lamellar structure) more uniformly when compared to the deposition on a higher surface energy substrate, which may lead to an improvement in ττ-π interactions between the neighbouring polymer chains or small molecules/oligomers, which in turn leads to an improvement in the field effect mobility of the transistor. In addition, the charge carrier transport in the horizontal axis across the channel region is favoured.

[0034] In addition or alternatively, the source electrode and/or drain electrode comprise(s) a second self-assembled monolayer on at least a part of a surface thereof, and the phase-separated thin film is formed in contact with said surface. More preferably, both source electrode and the drain electrode comprise a self-assembled monolayer which may be the same or different. By using such a configuration, the average saturation charge carrier mobility may be further improved.

[0035] Advantageously, in the configuration of the present invention, the provision of a first and/or second self-assembled monolayer has the advantage that vertical phase separation between the fluoropolymer phase and the organic semiconductor phase is enhanced.

[0036] The type of self-assembled monolayers used for the first and second self-assembled monolayers is not particularly limited as long as the surface energy of the substrate surface is decreased. While not being limited thereto, examples of suitable self-assembled layers and their preparation are disclosed in WO 2010/015833 A1 and in DiBenedetto et al., Adv. Mater. 2009, 21, 1407-1433.

[0037] As preferred materials for the first self-assembled monolayer, compounds exhibiting non-polar groups, such as C1-C40 alkyl groups, may be mentioned, as it has been found that they favourably interact with the organic semiconductor phase and thereby particularly promote vertical phase separation. Alkyl silanes or aryl silanes and their derivatives, such as e.g. octadecyltrichlorosilane (ODTS), are particularly preferred.

[0038] It is to be understood that the choice of materials for the second self-assembled monolayer is wider than that for the first self-assembled monolayer as the vertical phase separation and interaction with the organic semiconductor layer over the source and drain electrodes is less critical than over the channel region. Preferred materials for use as the second self-assembled monolayer include thiols (such as alkyl thiols, functionalized thiols, dithiols, ring thiols), one prominent example being pentafluorobenzene thiol (PFB thiol).

Method for the preparation of organic thin film transistors (OTFTs) [0039] In a further embodiment, the present invention relates to a method of manufacturing an organic thin film transistor (OTFT) comprising: preparing a substrate; forming a gate electrode on the substrate; providing a gate dielectric on the gate electrode; disposing source and drain electrodes over the gate dielectric with a channel region therebetween; and forming a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase over at least the channel region by vertical phase separation using depositing a blend solution comprising a small-molecule organic semiconductor and a fluorinated polymer. Details regarding the preferred embodiments of each of the components correspond to those outlined above with respect to the embodiment related to the OTFT.

[0040] The method according to the present invention has the advantage that it enables to provide the combination of an organic semiconductor layer and a polymer layer having low surface energy in one single step and thereby simplifies the OTFT manufacturing process, without the difficulties conventionally observed when combining fluorous polymers with dissimilar non-fluorinated materials. Moreover, the method ensures that the organic semiconductor layer is provided in the desired location in the OTFT layer stack, thereby enhancing the carrier mobility.

[0041] The formation of each of the gate, source and drain electrodes, the gate dielectric, and the optional first and second self-assembled monolayers present in the OTFT according to the present invention is not particularly limited to specific techniques and may be suitably chosen by the skilled artisan depending on the material to be deposited. While not being limited thereto, exemplary coating and deposition techniques include thermal deposition, vacuum deposition, laser deposition, screen printing, printing, imprinting, spin casting, dipping, ink-jetting, roll coating, flow coating, drop casting, spray coating, and/or roll printing.

[0042] The blend solution of organic semiconductor and fluorinated polymer should be formed at a weight ratio adequate for the phase separation. In an embodiment of the present invention, the weight ratio of the fluorinated polymer and the organic semiconductor may be set in the range of from about 1:99 to about 99:1, preferably in the range of from about 1:50 to 99:1 in view of the reduction of manufacturing costs. When using a solvent for the preparation of the blend solution, the solvent should be appropriately chosen so as to be capable of simultaneously dissolving the organic semiconductor and the fluorinated polymer, the typical amount of solvent used being in the range of 0.1 to 20 wt % based on the total weight of the blend solution. [0025] An annealing step as described in the method of US 8,828,793 B2 may be performed in order to further increase the degree of vertical phase separation and/or to increase the crystallinity of the organic semiconductor phase. OTFT applications [0043] In general, the OTFTs according to the present invention may be used in various electronic devices including flat panel displays, photovoltaic devices and sensors.

[0044] In one embodiment, the present invention relates to a sensing device comprising the above-described OTFT, preferably a biosensor.

[0045] Since the fluoropolymer phase exhibiting a favorably low surface energy and high hydrophobicity may form the surface exposed to the material to be detected, the applicability particularly in aqueous environments may be widened.

Examples [0046] OTFT devices having the configuration illustrated in Fig. 2 have been prepared as testing devices, using a substrate (11) made of glass, onto which a gate electrode (12) made of aluminum has been deposited, with AI2O3 serving as the gate dielectric/insulating layer (13). As source and drain electrodes (14) and (15), Au was deposited on the gate dielectric (13) so as to form a channel region therebetween over the gate electrode (12). Contacts (16a and 16b) made of silver were provided on each side of the OTFT. A first self-assembled monolayer (18c) was provided in the channel region by using octadecyltrichlorosilane (ODTS) and second self-assembled monolayers (18a and 18b) were provided on the source and drain electrodes (14) by using pentafluorobenzene thiol (PFB thiol). Thereafter, a substance selected from the materials shown in Tab. 1 have been deposited on the resulting structures, with FP1 denoting a co-polymer comprising the monomer units (A) and (B) (1:1), FP2 being a co-polymer comprising the monomer units (A) and (C) (1:1), and OSC1 denoting a small-molecule organic semiconductor (D), wherein compounds (A) to (D) have the following structural formulae:

(D) [0047] Deposition of the materials was accomplished by spin-coating solutions using trifluorotoluene (FP1), xylene (FP2, OSC1, FP2-OSC1), or xylene/trifluorotoluene (FP1-OSC1) as solvents (0.9% w/v in case of FP1-OSC1, 1.2% w/v in all other cases).

[0048] The contact angle of a drop of reference liquid placed on the surface of the respective layer or on the bare ODTS self-assembled monolayer was measured using an Automated Kruss Drop Shape Analyser (Model DSA100), measuring two duplicate plates sequentially with water and diiodomethane droplets to determine the dispersive and polar contributions to the surface energy. The results of the measurements are shown in Tab. 1 below.

[0049] The results in Table 1 show that among the control films, the fluoropolymer layers exhibit the lowest surface energies. More importantly, the blended films have lower surface energies than the OSC1 control, with the surface energy of the blended film FP1-OSC1 being lower and the surface energy of the blended film FP2-OSC1 being comparable to that of the respective fluoropolymer control films. It is thereby verified that using a fluorinated polymer in a blend with a small-molecule organic semiconductor effects vertical phase separation resulting in a phase-separated thin film.

[0050] TABLE 1: Surface energy calculations from contact angle measurements

[0051] In addition, the transfer characteristics of OTFT devices having the same configuration as the above testing devices have been studied, wherein in one OTFT, the layer comprising organic semiconductor (17) has been provided by using a blend comprising OSC1 as a small-molecule organic semiconductor and FP1 as a fluorinated polymer, and in the other OTFT, P1, a non-fluorinated analogue of FP1, has been used instead of FP1. The transfer performance of OTFTs comprising the fluoropolymer FP1 is shown in Fig. 3. and the transfer performance of OTFTs comprising the non-fluorinated analogue P1 is shown in Fig. 4, each in comparison with a control OTFT without OSC1.

[0052] Figures 3 and 4 demonstrate that carrier mobility is remarkably increased by using a fluorinated polymer in a blend with a small-molecule organic semiconductor, which thus shows that migration of the organic semiconductor OSC1 to the gate/channel region has occurred and a phase-separated thin film has been formed.

REFERENCE NUMERALS 1/11 - substrate 2/12 - gate electrode 3/13 - gate dielectric/insulating layer 4/14 - source electrode 5/15 - drain electrode 6 - channel region 7 - phase-separated thin film 7a - fluoropolymer phase 7b - organic semiconductor phase 16a/16b - contact 17 - layer comprising organic semiconductor 18a/18b - second self-assembled monolayer 18c - first self-assembled monolayer 19 - sample solution

Claims

1. An organic thin film transistor (OTFT) comprising: a substrate; a gate electrode formed on the substrate; a gate dielectric on the gate electrode; source and drain electrodes over the gate dielectric with a channel region therebetween; and a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase over at least the channel region formed by vertical phase separation from a blend comprising a small-molecule organic semiconductor and a fluorinated polymer.

2. The organic thin film transistor (OTFT) according to claim 1, wherein the surface energy of the fluoropolymer is lower than that of the small-molecule organic semiconductor.

3. The organic thin film transistor (OTFT) according to any of claims 1 or 2, wherein the organic semiconductor phase is in contact with the channel region.

4. The organic thin film transistor (OTFT) according to any of claims 1 to 3, wherein the gate dielectric comprises a first self-assembled monolayer on at least part of the surface of the channel region on which the phase-separated thin film is formed.

5. The organic thin film transistor (OTFT) according to claim 4, wherein the first self-assembled monolayer is a monolayer is formed from materials selected from alkyl silanes, aryl silanes and derivatives thereof.

6. The organic thin film transistor (OTFT) according to any of claims 1 to 5, wherein the source electrode and/or drain electrode comprise(s) a second self-assembled monolayer on at least a part of a surface thereof, and the phase-separated thin film is formed in contact with said surface.

7. The organic thin film transistor (OTFT) according to any of claims 1 to 6, wherein the fluorinated polymer is a conjugated polymer.

8. The organic thin film transistor (OTFT) according to any of claims 1 to 7, wherein he fluorinated polymer has a fluorine content of at least 10 wt.-%.

9. The organic thin film transistor (OTFT) according to any of claims 1 to 8, wherein the small molecule organic semiconductor is a thiophene-based derivative comprising linear or branched C3-C30 alkyl groups.

10. Sensing device comprising the organic thin film transistor (OTFT) according to any of claims 1 to 9.

11. Sensing device according to claim 10, wherein the sensing device is a biosensor.

12. Method of manufacturing an organic thin film transistor (OTFT) comprising: preparing a substrate; forming a gate electrode on the substrate; providing a gate dielectric on the gate electrode; disposing source and drain electrodes over the gate dielectric with a channel region therebetween; and forming a phase-separated thin film comprising an organic semiconductor phase and a fluoropolymer phase over at least the channel region by vertical phase separation using depositing a blend solution comprising a small-molecule organic semiconductor and a fluorinated polymer.

13. Use of a blend solution comprising a small-molecule organic semiconductor and a fluorinated polymer to promote vertical phase separation during manufacture of a bottom-gate organic thin film transistor (OTFT).