WO2023091046A1

WO2023091046A1 - Method of fabricating thin-film semiconductor photovoltaic converters

Info

Publication number: WO2023091046A1
Application number: PCT/RU2021/000546
Authority: WO
Inventors: Anastasiya Sergeevna YAKUSHEVA; Danila Sergeevich SARANIN; Dmitry Sergeevich MURATOV; Lev Olegovich LUCHNIKOV; Pavel Andreevich GOSTISHCHEV; Denis Valerievich KUZNETSOV; Sergei Ivanovich DIDENKO; Al'do DI CARLO
Original assignee: National University Of Science And Technology "Misis"
Priority date: 2021-11-16
Filing date: 2021-12-07
Publication date: 2023-05-25

Abstract

This invention relates to the technology of thin-film hybrid semiconductor photovoltaic converand can be used for the fabrication of solar cells and solar cell arrays as well as photodetectors and other types of photovoltaic converters. Method of fabricating thin-film semiconductor photovoltaic converters based on halogenide perovskites wherein in said photovoltaic converter comprising an anodic electrode, a selectively transporting layer having the p type conductivity, a photo absorbing layer, a electrode, a selectively transporting layer having the n type conductivity and a cathodic electrode located in sequence on a substrate, a buffer layer in the form of a composite material is provided using a liquid phase technique between said selectively transporting layer having the n type conductivity and said cathodic electrode.

Description

Method of Fabricating Thin-Film Semiconductor Photovoltaic

Converters

Field of Invention. This invention relates to the technology of thin-film hybrid semiconductor photovoltaic converters and can be used for the fabrication of solar cells and solar cell arrays based on halogenide perovskites as well as photodetectors and other types of photovoltaic converters containing a composite buffer layer with MXenes (Ti₃C₂Tx) in their structure.

Prior Art. Known is a technology of MXene incorporation into the absorber layer of perovskite solar cells [Zhanglin Guo et al., High Electrical Conductivity 2D MXene Serves as Additive of Perovskite for Efficient Solar Cells, Small, https://doi.org/10.1002/smll.201802738; 2018 pp: 1802738]. Mxene s incorporated into the perovskite absorber layer for efficiency enhancement. Results show that the Mxene incorporation can retard the crystallization rate, thereby increasing the ABX₃ crystal size of (CH₃NH₃PbI₃). It is found that the high electrical conductivity and mobility of MXene can accelerate the charge transfer. After optimizing the key parameters, 12% enhancement in device performance is achieved by 0.03 wt% amount of MXene additive.

A disadvantage of said technology is the lack of allowance for the stabilization of the electrode contacts and heterojunction boundaries upon 0.03 wt% MXene addition. Simultaneously the result achieved in the cited work demonstrates a low gain in solar cell efficiency, i.e., at a 1-2% level of the initial device efficiency.

Known is technology of MXene use in p-i-n perovskite solar cells [https://doi.Org/10.1016/j.nanoen.2021.105771] wherein MXene addition permits to tune the energy level alignment at perovskite/charge transporting layer interfaces, and on the other side to passivate traps states within the cell structure, which in turn improves charge extraction and collection at the electrodes with power conversion efficiency exceeding 19%. Due to the possibility to finely tune the MXene work function during their chemical synthesis and to their capability in modifying the optoelectronic properties of PSC layers when used as dopant, the proposed approach opens countless ways for engineering inverted PSC structure and future scalability.

A disadvantage of said approach is the lack of information on the capability to increase device stability with demonstration of prototyped implementation of this effect.

The closest counterpart of the invention claimed herein is a method of fabricating perovskite solar cells with an electron transporting layer doped with MXenes with F-functionalization (CN 113013335 A, published 22.06.2021). Said method discloses an electron transporting layer based on a fullerene derivative (method alcohol-phenyl-C61 -butyric acid, PCBM) doped with MXenes and fluorine functionalization for perovskite solar cells. The use of MXenes provides for energy level alignment in the device and increases the operation stability of solar cells due to enhancement of the hydrophobicity of the PCBM layer.

A disadvantage of said method is the elimination of only one local factor causing the degradation of perovskite solar cells upon moisture saturation which is not the predominant degradation factor of perovskite photo absorbing structures.

The problem targeted by the method developed herein is the degradation of the device parameters, e.g. idle voltage (Vi), short circuit current (I_sc), currentvoltage curve (CV) fill factor (F_f) and device efficiency, caused by corrosion and electrochemical interaction at the thin film interfaces in the structure of perovskite photovoltaic converters under various external factors, e.g. elevated temperatures (to 80 °C) and illumination (100 mW/cm²). Corrosion and electrochemical interaction in perovskite photovoltaic converters are directly triggered by the segregation of defects, uncompensated lattice ions, substitutional atoms and vacancies. The formation of the abovementioned defects and structural imperfections occurs during the synthesis of microcrystalline films. An increase in the concentration of defects in the thin-film structures of photovoltaic converters is observed during the degradation of ordered perovskite lattice structures under external factors, e.g. illumination and elevated temperatures. Disclosure of the Invention. The technical result achieved in the invention disclosed herein is a multifold increase in the stability of the device parameters of photovoltaic converters (solar cells, photodiodes, photodetectors) based on halogenide pervoskites under illumination and elevated temperatures.

Said technical result is achieved as follows.

Method of fabricating thin-film semiconductor photovoltaic converters based on halogenide perovskites wherein in said photovoltaic converter comprising an anodic electrode, a selectively transporting layer having the p type conductivity, a photo absorbing layer, a electrode, a selectively transporting layer having the n type conductivity and a cathodic electrode located in sequence on a substrate, a buffer layer in the form of a composite material is provided using a liquid phase technique between said selectively transporting layer having the n type conductivity and said cathodic electrode. Said composite material is synthesized from a dispersion solution produced by dispersion of Ti₃C₂T_x MXenes where T_x is a mixture of F', Cl', O' and OH' functional groups at concentrations of 0.50 mg/ml to 0.75 mg/ml in a medium of diluted solutions of low molecular weight organic semiconductors (LOS).

Said LOS solutions are produced with a concentration of 0.5 mg/ml in dehydrated organic solvents.

Said MXenes are in the form of microdispersed powders of Ti₃C₂T_x phase scales with the flake cross-sectional sizes being 1-2 nm, an electrical conductivity of at least 3200 S^cm'¹, a fluorine percentage of up to 15 at.%, a percentage of bound forms of oxygen and hydroxyl groups of up to 20 at.% and a chlorine percentage of up to 2 at.%, wherein said MXenes are produced by chemical exfoliation from the MAX phase (Ti₃AlC₂ ) with an HF or LiF/HCl solution.

Furthermore said low molecular weight organic semiconductors can be bathocuproine (C₂₆H₂₀N₂) or biphene (C₂₄HI₆N₂) or nitrogen-containing counterparts for selective transport with n and p type conductivity.

Furthermore said dehydrated organic solvents can be alcohol solvents of at least 99% purity, e.g. methanol or ethanol or isopropanol. Furthermore dispersion of MXenes Ti₃C₂T_x can be accomplished with permanent stirring for 24 h and preliminary ultrasonication for 1 h.

Furthermore said liquid phase method of buffer layer synthesis on said selectively transporting layer having the n type conductivity is implemented by printing, spraying or centrifugation.

An advantage of this invention is a substantial increase in the long-term stability of the device parameters of perovskite photovoltaic converters without complication or variation of the semiconductor device process, using liquid phase functional layer synthesis methods, achieved by replacement of layers conventionally used for the selective collection of carriers in the form of low molecular weight organic semiconductors (LOS) for layers according to this invention in the form of a composite material additionally containing MXenes (LOS-MXenes).

Replacement of LOS or another selectively transporting material for pure MXenes would not provide for the formation of a homogeneous interlayer of said material which is of special importance from the viewpoint of device area scalability. The use of a composite material synthesized using liquid phase application of MXene dispersion in a LOS solution solves the task of homogeneous application of a low-dimensional material at a high concentration and its most efficient use as an agent for chemical and structural stabilization of the interface providing for long-term operation of the entire perovskite photovoltaic converter with the minimal compromise in the device performance.

The final result of MXene introduction into the structure of perovskite photovoltaic converters is a multifold increase in the service life of the semiconductor device with the minimal compromise in the device performance.

Brief Description of the Drawings

The invention will be exemplified below with Figures wherein Fig. 1 shows the architecture of the p-i-n perovskite photovoltaic converter where the p layer is the layer conducting positive charges, i.e., holes, i is the perovskite photo absorber layer and n is the layer conducting negative charges, i.e., electrons, which is typical of semiconductor devices as solar cells, photodiodes and photodetectors; Fig. 2 shows the architecture of the p-i-n perovskite photovoltaic converter with a buffer layer in the form of a composite material comprising MXenes for device parameter stabilization; Fig. 3 shows the architecture of the n-i-p perovskite photovoltaic converter which is typical of semiconductor devices as solar cells, photodiodes and photodetectors; Fig. 4 shows the architecture of the n-i-p perovskite photovoltaic converter with a buffer layer in the form of a composite material comprising MXenes for device parameter stabilization; Fig. 5 shows time dependences of normalized device efficiency for operation under permanent photosaturation for perovskite solar cells with an without the LOS-MXenes composite layer synthesized in various configurations; Fig. 6 shows time dependences of normalized device efficiency for operation under permanent heating to 80 °C for perovskite solar cells with an without the LOS-MXenes composite layer synthesized in various configurations; Fig. 7 shows current-voltage curves of for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively; Fig. 8 shows spectral curves of external quantum efficiency for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively; Fig. 9 shows measured stability of the maximum power for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively, with permanent illumination: spectrum 1.5 AM g, power 100 mW/cm² with heating to 65 °C.

Figs. 1-9 show the following components:

Substrate 1, anodic electrode 2, selectively transporting layer having the p type conductivity 3„ photo absorber layer 4, selectively transporting layer having the n type conductivity 5, hole blocking layer 6, cathodic electrode 7, buffer layer 8, electron blocking layer 9 and buffer layer 10;

Curve 11 is normalized efficiency vs time dependence under permanent photosaturation for a perovskite solar cell without LOS-MXenes composite; Curve 12 is normalized efficiency vs time dependence under permanent photosaturation for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 0.50 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curve 13 is normalized efficiency vs time dependence under permanent photosaturation for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 0.75 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curve 14 is normalized efficiency vs time dependence under permanent photosaturation for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 1.00 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curve 15 is normalized efficiency vs time dependence under permanent heating to 80 °C for a perovskite solar cell without LOS-MXenes composite;

Curve 16 is normalized efficiency vs time dependence under permanent heating to 80 °C for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 0.50 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curve 17 is normalized efficiency vs time dependence under permanent heating to 80 °C for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 0.75 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curve 18 is normalized efficiency vs time dependence under permanent heating to 80 °C for a perovskite solar cell with LOS-MXenes buffer layer synthesized from dispersion of MXenes with a concentration of 1.00 mg/ml in a diluted LOS solution in dehydrated organic solvents;

Curves 19 and 20 are current- voltage curves for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively; Curves 21 and 22 are spectral curves of external quantum efficiency for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively;

Curves 23 and 24 are measured stability of the maximum power for perovskite solar cells with a buffer layer in the form of a composite material comprising and not comprising MXenes, respectively, under permanent illumination: 1.5 AM G spectrum, power 100 mW/cm² with heating to 65 °C.

The photovcoltaic converter based on halogenide perovskites synthesized using the method in accordance with this invention comprises on substrate 1 the sequence of anodic electrode 2, selectively transporting layer having the p type conductivity 3„ photo absorber layer 4, selectively transporting layer having the n type conductivity 5 and cathodic electrode 7, with buffer layer 8 being located between layer 5 and electrode 7.

Substrate 1 is a bearing element on which all the photovoltaic converter functional layers are provided: plastics, quartz and other optically transparent materials as well as foils and metallic sheets.

Anodic electrode 2 is a layer based on a conducting material, e.g. In₂O₃:SnO₂ (ITO, Al₂O₃:ZnO and its counterparts, thin metallic layers (Ag, Ni, Cu etc.) and layers of low-dimensional materials (graphene and its counterparts in the form of nanotubes or nanowires). Said anodic layer is used for the collection of positive charge, i.e., holes, and is optically transparent.

Selectively transporting layer having the p type conductivity 3 is a thin-film coating based on wide-band oxides (NiO_x, CuO_x etc.) or organic semiconductors (Poly-3-hexyl thiophene etc.) providing for the transportation of holes injected from photo absorber layer 4.

Photo absorber layer 4 is a thin-film coating based on halogenide perovskites (general chemical formula APbX₃, where A is a cation such as CH₃NH₃ ⁺ or (NH₂)₂CH⁺ or C(NH2)₃ ⁺, other organic cations, Cs⁺, Rb⁺ or a mixture thereof and X is an anion such as Cf , Br‘, T or a mixture thereof). Selectively transporting layer 5 is a thin-film coating having the n type conductivity based on wide-band oxides (TiO_x, SnO_x etc.) and organic semiconductors (C₆₀ and its counterparts acting as transport materials) providing for the transport of electrons injected from photo absorber layer 4.

Hole blocking layer 6 is a thin-film coating .based on LOS, e.g. bathocuproine (2,9-dimethyl-4,7-diphenyl- 1 , 10-phenanthroline, C26H20N2); biophene (4, 7-diphenyl- 1,10-phenanthroline, C₂4HI₆N₂) and their counterparts exhibiting selective transport properties.

Cathodic electrode 7 is in the form of thin metallic layers (Ag, Ni, Cu etc.), a coating of transparent conducting materials, e.g. In₂O₃:SnO2 (ITO and its counterparts) or layers of low-dimensional materials (graphene and counterparts, nanotubes and nano wires).

Buffer layer 8 is a composite material .based on hole blocking LOS with MXenes Ti₃C₂T_x (where T_x is a mixture of F', Cf, O’, OH’ functional groups).

Electron blocking layer 9 is a thin-film coating .based on LOS (e.g. N, N-di (1 -naphthyl) - N, N-diphenyl - (1,1 -biphenyl) - 4,4-diamine) and its counterparts exhibiting selective transport properties.

Buffer layer 10 is a composite material .based on electron blocking LOS with MXenes Ti₃C₂T_x, where T_x is a mixture of F’, C1’,O’ and OH’ functional groups.

In the thin-film semiconductor photovoltaic converter process, layer 5 is coated with buffer composite layer 8 using a liquid phase method implemented by printing, spraying or centrifugation.

Composite buffer layer 8 is synthesized by dispersion of MXenes Ti₃C₂T_x , where T_x is a mixture of F’, Cf, O’ and OH’ functional groups, with their concentration varying from 0.50 to 0.75 mg/ml in LOS solutions diluted in dehydrated organic solvents with a concentration of up to 0. 5 mg/ml.

Said MXenes are in the form of fine powders of phase Ti₃C2Tx scales with the flake cross-sectional sizes being 1-2 nm, an electrical conductivity of at least 3200 S*cm’‘, a fluorine percentage of up to 15 at.%, a percentage of bound forms of oxygen and hydroxyl groups of up to 20 at.% and a chlorine percentage of up to 2 at.%. The MXenes can be synthesized by chemical exfoliation from MAX phase with an HF or LiF/HCl solution.

Said LOS can be bathocuproine or biphene or nitrogen containing counterparts for selective transport of n and p type conductivity and the dehydrated organic solvents can be alcohol solvents of at least 99% purity, e.g. methanol or ethanol, isopropanol or similar solvents.

Dispersion is accomplished with permanent stirring for 24 h and preliminary ultrasonication for 1 h.

Presented below are specific embodiments of this invention for solar cells .based on halogenide perovskites.

Embodiment 1.

This embodiment demonstrates the possibility of achieving the claimed technical result at an MXene concentration of 0.50 mg/ml in diluted LOS solutions in dehydrated organic solvents.

Perovskite solar cell (PSC) is fabricated in the p-i-n structure configuration in accordance with Fig. 2.

The PSC device structure is fabricated on Soda Lime glass substrates (thickness 1.1 mm) with a ITO coating acting as anodic electrode. The surface electrical resistivity of ITO is 15 Ohm/sq.

The ITO coated glass substrates are cleaned from organic contamination and dust by ultrasonication for 20 min in organic solvents, i.e., extra purity acetone and isopropanol (>99.8 %).

Then the ITO coated glass substrates are deep UV treated (wavelength 210 nm) for providing hydrophilic properties of the surface before liquid phase application of thin films.

Liquid phase synthesis of p type conductivity NiO_x transport layer is accomplished using nickel chloride solution (NiCf, 99.9 % purity) produced by salt dissolution at a 20 mg/ml concentration in deionized water. The p type conductivity NiO_x transport layer forms upon application of the NiCl₂ solution onto ITO coated glass substrates by centrifugation (spin coating) in an air atmosphere. Centrifugation is carried out at a substrate rotation speed of 1500 rps for 60 sec. Then the substrates with applied coating are annealed at 300 °C for 1 h. The thickness of the NiO_x layer so synthesized is 40 nm.

The photo absorber layer is a thin halogenide perovskite film having the chemical composition Cso.2(CH₃(NH₂)2)o.8PbI₃ (hereinafter, CsFAPbI₃). The photo absorber layer is synthesized by liquid phase application of the perovskite solution by centrifugation, anti-solvent treatment and thermal annealing. The perovskite solution with a concentration of 1.4 M is produced in a mixture of solvents, i.e., dimethylformamide (DMFA, 99.8%, dehydrated) / dimethylsulfoxide (DMSO, 99.9 %, dehydrated) in a 4:1 volume ratio upon dissolution of CsI salts (99.999 % purity), CH₃(NH₂)2l (99.99 % purity) and Pbl₂ (99.999% purity) in a 0.2:0.8:1 molar ratio, respectively. For complete salt dissolution in the perovskite solution the solution is heated to 70 °C for 4 h. Before the application of the CsFAPbI₃ photo absorber layer the perovskite solution is filtered through a 0.45 Dm Teflon filter. The CsFAPbI₃ photo absorber layer forms upon perovskite solution application upon the p type conductivity NiO_x transport layer on the ITO coated glass substrate by centrifugation in an inert argon gas atmosphere. Centrifugation is carried out at a substrate rotation speed of 5000 rps for 1 min. For triggering the crystallization of the photo absorber layer during centrifugation from the solution the substrate is coated with an anti-solvent, i.e., chlorobenzene (998 % purity, dehydrated). The film is annealed at 100 °C for 10 min. The thickness of the photo absorber layer so synthesized is 450 nm.

The n type conductivity transport layer is thin film of organic semiconductor C₆₀ applied upon the photo absorber CsFAPbI₃ layer. The n type conductivity transport layer is synthesized by thermoresistive sputtering of C₆₀ powder (99.9 % purity) in deep vacuum at 10'° Pa and a growth rate of 0.02 nm/s. The thickness of the C₆₀ layer so synthesized is 40 nm. For the application of the LOS-MXenes composite layer at the interface between the n type conductivity transport layer and the cathodic electrode, a dispersion of MXenes in a diluted LOS solution is prepared. The diluted LOS solution is produced by addition of bathocuproine compound (99.5% purity) with a concentration of 0.5 mg/ml to extra purity dehydrated isopropanol (99.9%). Complete dissolution of bathocuproine is achieved by solution heating to 50 °C with intense stirring for 5 h. A dispersion of MXene is synthesized by addition of microdisperse MXene powder with a concentration of 0.5 mg/ml to a diluted LOS solution, stirring for 24 h and subsequent ultrasonication for 1 h with the aim to provide a homogeneous distribution of bathocuproine and 2D MXene particles. The LOS-MXenes composite layer is synthesized by liquid phase application of MXenes dispersion in the diluted LOS solution by centrifugation in an inert argon gas atmosphere. Centrifugation is carried out at a substrate rotation speed of 4000 rps for 60 sec. Then the substrates with applied coating are annealed at 50 °C for 5 min. The thickness of the composite layer so synthesized is 10 nm.

The copper (Cu) cathodic electrode is fabricated by a thermoresistive method in vacuum through masks at a 0.1 nm/s rate for the formation of the device structure with a photosensitive region having the preset area of 0.14 cm .

After the fabrication of the device structure with the electrodes the device is packaged by applying a UB adhesive onto the device structure and lamination with 1 mm thick covering glass. The UV adhesive is hardened upon near-range UV (380) nm treatment for 20 min.

The achievement of the technical result of this invention for vdifferent MXenes concentrations in the composite layer was judged about by comparing with the device configurations in which the hole blocking layer was a LOS layer without additions (as follows from Fig. 1 the concentration of MXenes in the composite material is 0.0 mg/ml, hereinafter references).

The criteria of technical result achievement were a change in the device parameters (Vi, I_sc, F_f and efficiency) and stability of efficiency in time under permanent illumination (photosaturation) and permanent heating. The changes in the device parameters of the synthesized PSC were evaluated by measuring the current-voltage curves under standard conditions of incident light, i.e., 1.5 AM G spectrum, incident light power of 100 mW/cm , AAA grade solar imitator spectrum and calibration against a reference photovoltaic converter.

For evaluating the stability of the device efficiency under permanent illumination (photosaturation) the PSC was exposed to light with 1.5 AM G spectrum and an incident light power of 100 mW/cm² without electric load (idle mode). The change in the device efficiency was evaluated by measuring the current- voltage curves at 50 h intervals. The tests were conducted in a room with an air atmosphere and an ambient temperature of 22 ± 2 °C. The stability of the device efficiency for the PSC was evaluated by time in which the efficiency declined to 80% of the initial figure.

For evaluating the stability of the device efficiency under permanent heating to 80 °C the PSC were exposed to heating in a thermostated furnace without electric load (idle mode). The change in the device efficiency was evaluated by measuring the current-voltage curves at 50 h intervals. The stability of the device efficiency for the PSC was evaluated by time in which the efficiency declined to 80% of the initial figure.

The device parameters of the PSC fabricated in accordance with Embodiment 1 are summarized in Table 1.

The time parameters of device efficiency stability under photosaturation for the PSC fabricated in accordance with Embodiment 1 are summarized in Table 2.

The time parameters of device efficiency stability under permanent heating for the PSC fabricated in accordance with Embodiment 1 are summarized in Table 3.

Embodiment 2.

This embodiment demonstrates the possibility of achieving the claimed technical result at a MXene concentration of 0.75 mg/ml in diluted LOS solutions in dehydrated organic solvents. Perovskite solar cell (PSC) is fabricated in the p-i-n structure configuration in accordance with Fig. 2. The PSC fabrication method in accordance with Embodiment 2 implies the use of a 0.75 mg/ml MXene concentration for the production of a MXene dispersion in a diluted LOS solution, the other process parameters and sequence being the same as in Embodiment 1.

The device parameters of the PSC fabricated in accordance with Embodiment 2 are summarized in Table 1.

The time parameters of device efficiency stability under photosaturation for the PSC fabricated in accordance with Embodiment 2 are summarized in Table 2.

The time parameters of device efficiency stability under permanent heating for the PSC fabricated in accordance with Embodiment 2 are summarized in Table 3.

Embodiment 3.

This embodiment demonstrates the possibility of achieving the claimed technical result at a MXene concentration of 1.00 mg/ml in diluted LOS solutions in dehydrated organic solvents.

Perovskite solar cell (PSC) is fabricated in the p-i-n structure configuration in accordance with Fig. 2. The PSC fabrication method in accordance with Embodiment 3 implies the use of a 1.00 mg/ml MXene concentration for the production of a MXene dispersion in a diluted LOS solution, the other process parameters and sequence being the same as in Embodiment 1.

The device parameters of the PSC fabricated in accordance with Embodiment 3 are summarized in Table 1.

The time parameters of device efficiency stability under photosaturation for the PSC fabricated in accordance with Embodiment 3 are summarized in Table 2.

The time parameters of device efficiency stability under permanent heating for the PSC fabricated in accordance with Embodiment 3 are summarized in Table 3.

The use of the LOS-MXenes composite for the synthesis of a p-i-n architecture of perovskite photovoltaic converter allows improving the device parameters and their stability under intense light (1.5 AM G spectrum and incident light power of 100 mW/cm²) and under heating (to 80 °C).

The concentration of MXenes used for dispersion in the LOS solution significantly affects the change in the device parameters of photovoltaic converters based on halogenide perovskites and has an optimum range from 0.50 mg/ml to 0.75 mg/ml in which the device efficiency increases.

The optimum MXene concentrations for the fabrication of composite layers were determined empirically by analyzing the changes in the device parameters of the perovskite solar cells, i.e., idle voltage Vi, short circuit current density J_sc, fill factor F_f and efficiency. The device parameters were measured under standard conditions (1.5 AM G spectrum and incident light power of 1000 Watts/meter ) with an AAA grade solar radiation imitator having a xenon light source and a reference cell for calibration. The measurements were conducted for devices fabricated with the use of LOS-MXenes composite and for reference devices in which the hole blocking layer was a LOS layer without additions (in accordance with Fig. 1). Replacement of a single-component LOS layer for LOS-MXenes composite in accordance with Fig. 2 improves the device parameters. Dependence of the PSC device parameters on MXene concentration in LOS solution is summarized in Table 1 showing average parameters with rms deviation calculated from data on 15 specimens for each configuration.

For the fabrication technology exemplified in Fig. 1 the reference devices demonstrated an average efficiency of (15.1 ± 0.66)% with Vj = (1.01 ± 0.01) V, I_sc = (20.60 ± 0.87) mA/cm² and F_f = 0.69 ± 0.03. An increase in the device parameters for devices with a LOS -MXene composite layer was only achieved for the composite produced in a LOS solution with MXene concentrations of 0.50 and 0.75 mg/ml, respectively. The results suggest that the devices with a composite layer synthesized for a MXene concentration of 0.50 mg/ml in a LOS solution demonstrate the highest efficiency in comparison with the other configurations and are optimum. The average device parameters of the PSC with a composite layer synthesized for a mXene concentration of 0.75 mg/ml demonstrated the largest increase in comparison with the reference devices with respect to the parameters Vj = (1.04 ± 0.01) V (+0.03 V against the reference devices), I_sc = (22.22 ± 0.65) mA/cm² (+1.05 mA/cm² against the reference devices), F_f = (0.77 ± 0.03) (+0.02 against the reference devices) and efficiency of (16.2 ± 0.63)% (+ 0.9% against the reference devices). Increasing the MXene concentration to above 0.75 mg/ml in a LOS solution dispersion caused a dramatic decline in the PSC efficiency which is mainly demonstrated by losses in short circuit current density and in idle voltage.

Evaluation of the effect of the use of the LOS-MXene composite material on the stability of efficiency in time under external degradation factors is the most important from the viewpoint of achieving the technical result claimed herein. Analysis of the data on the change in the device efficiency under permanent photosaturation (incident radiation power density of 100 mW/cm ) for the PSC fabricated in accordance with Embodiments 1 -3 demonstrates that the use of the LOS-MXene composite material increases the stability of the device efficiency for MXene concentrations of 0.50-0.75 mg/ml in the LOS solution.

For the devices with the composite layer synthesized at an MXene concentration of 0.50 mg/ml in the LOS solution the increase in the stability was +37.5% compared with the reference devices (the stable operation time increased from 960 h to 1320 h).

For the devices with the composite layer synthesized at an MXene concentration of 0.75 mg/ml in the LOS solution the increase in the stability was +81.7% compared with the reference devices (the stable operation time increased from 960 h 1745 h).

For the devices with the composite layer synthesized at an MXene concentration of 1.00 mg/ml in the LOS solution the increase in the stability was insignificant, i.e., +0.2% compared with the reference devices (the stable operation time increased from 960 h 962 h).

It was therefore concluded that the devices with the composite layer synthesized at an MXene concentration of 0.75 mg/ml in the LOS solution demonstrate the highest stability of efficiency under photosaturation compared with the other configurations and are optimum.

Analysis of the data on the change in the device efficiency under permanent heating to 80 °C for the PSC fabricated in accordance with Embodiments 1-3 demonstrates that the use of the LOS-MXene composite material increases the stability of the device efficiency for MXene concentrations of 0.50-0.75 mg/ml in the LOS solution.

For the devices with the composite layer synthesized at an MXene concentration of 0.50 mg/ml in the LOS solution the increase in the stability was +30.6% compared with the reference devices (the stable operation time increased from 375 h 490 h).

For the devices with the composite layer synthesized at an MXene concentration of 0.75 mg/ml in the LOS solution the increase in the stability was achieved at the level of +81.7% compared with the reference devices (the stable operation time increased from 960 hours 1745 hours).

For the devices with the composite layer synthesized at an MXene concentration of 1.00 mg/ml in the LOS solution the increase in the stability was multifold, i.e., by 2.24 times compared with the reference devices (the stable operation time increased from 375 h 1060 h).

It was therefore concluded that the devices with the composite layer synthesized at an MXene concentration of 1.00 mg/ml in the LOS solution demonstrate the highest stability of efficiency under photosaturation compared with the other configurations.

Integral analysis of the use of the LOS-MXene composite material on the device parameters and the stability of the device efficiency for the PSC according to Embodiments 1 -3 showed that the optimum configuration is the one according to Embodiment 2. The use of 0.75 mg/ml concentration for the production of MXene dispersion in LOS solution provides for the highest device efficiency, highest stability of device efficiency under photosaturation and a significant increase in the device stability under permanent heating. The use of 0.50 mg/ml concentration for the production of MXene dispersion in LOS solution (Embodiment 1) also increases the device parameters and stability of efficiency under external degradation factors.

The use of 1.00 mg/ml concentration for the production of MXene dispersion in LOS solution (Embodiment 3) provides for the highest stability of device efficiency under permanent heating but has a deleterious effect on the device parameters.

Table 1. Dependence of device parameters of perovskite solar cells on MXene concentration in LOS solution used (average figures with rms deviation)

Table 2. Dependence of device efficiency stability of perovskite solar cells on MXene concentration in LOS solution used under permanent photosaturation

Table 3. Dependence of device efficiency stability of perovskite solar cells on

MXene concentration in LOS solution used under permanent heating to 80 °C

Comparison of the device parameters for the PSC with the highest efficiency for the reference configuration and for LOS-MXene composite layer synthesized with the optimum MXene concentration (0.75 mg/ml) is presented in Table 4. Table 4. Device parameters for the perovskite solar cells with the LOS-MXene buffer composite layer (0.75 mg/ml) with the highest efficiency obtained

Comparison of the PSC having the highest efficiency suggests that the relative growth of the idle voltage is more than 2.9% (+0.02 V) for PSC with a LOS-MXene composite layer instead of a single-component LOS layer. The relative growth of J_sc is more than 4.8% (+0.56 mA/cm²) for PSC with a LOS- MXene composite layer (0.75 mg/ml) instead of a single-component LOS layer. This entails an increase in the device efficiency since the use of a two-component LOS-MXene composite material instead of a single-component LOS layer provides for an increase in the device efficiency from 16.45 % to 17.46 % in accordance with the experimental data shown in Fig. 7 which shows the currentvoltage curves of the perovskite solar cells measured under standard conditions of incident light, i.e., 1.5 AM G spectrum, incident light power of 100 mW/cm , AAA grade solar imitator spectrum and calibration against a reference photovoltaic converter. Curve 19 in Fig. 7 shows the current- voltage curve for the photovoltaic converter with LOS as the hole blocking layer and Curve 20 in Fig. 7 shows the current-voltage curve for the photovoltaic converter with LOS-MXenes composite material.

The use of the LOS-MXenes composite material also increases the spectral conversion efficiency of photovoltaic converters in the entire perovskite layer absorption range as shown in Fig. 8 for prototyped devices. The spectral parameters (the external quantum efficiency) are shown in Fig. 8 which shows an increase in the spectral conversion efficiency in the 300 - 800 nm region. Curve 21 in Fig. 8 shows the external quantum efficiency for the photovoltaic converter with LOS as the hole blocking layer and Curve 22 in Fig. 8 shows the external quantum efficiency for the photovoltaic converter with LOS-MXenes composite material. The improvement of the external quantum efficiency is attributable to a higher efficiency of electron collection in the perovskite solar cells.

Of fundamental importance is the effect of the use of the LOS-MXenes composite material on the stability of the maximum power output, i.e., in constant load mode. Measurements of the stability of the maximum power output were conducted under permanent illumination (1.5 AM G spectrum and a power of 100 mW/cm ) and heating (to 65 °C), and changes in the maximum power in time are shown in Fig. 9, respectively.

The sue of MXene dispersion in a LOS solution with a 0.75 mg/ml concentration for the synthesis of the composite layer in photovoltaic converters increases the stability of the maximum power of perovskite solar cells under permanent photosaturation (1.5 AM G spectrum imitating solar radiation with a light power of 100 mW/cm²) and heating to 65 °C from approx. 450 h to more than 2500 h taking into account the relative reduction in the device efficiency to 80% of the initial figure (Fig. 9). Curve 23 in Fig. 9 shows the change in the normalized maximum power for the photovoltaic converter fabricated with LOS as the hole blocking layer and Curve 24 in Fig. 9 shows the change in the normalized maximum power for the photovoltaic converter fabricated with LOS-MXenes composite material under permanent heating to 65 °C and illumination with 1.5 AM G spectrum light with a power of 1000 Watts/meter².

Claims

What is claimed is a

1. Method of fabricating thin-film semiconductor photovoltaic converters based on halogenide perovskites wherein in said photovoltaic converter comprising an anodic electrode, a selectively transporting layer having the p type conductivity, a photo absorbing layer, a electrode, a selectively transporting layer having the n type conductivity and a cathodic electrode located in sequence on a substrate, a buffer layer in the form of a composite material is provided using a liquid phase technique between said selectively transporting layer having the n type conductivity and said cathodic electrode. Said composite material is synthesized from a dispersion solution produced by dispersion of Ti₃C₂T_x MXenes where T_x is a mixture of F’, Cl’, O’ and OH’ functional groups at concentrations of 0.50 mg/ml to 0.75 mg/ml in a medium of diluted solutions of low molecular weight organic semiconductors (LOS) in dehydrated organic solvents with a concentration of 0.5 mg/ml.

2. Method of Claim 1 wherein said MXenes are in the form of microdispersed powders of Ti₃C₂T_x phase scales with the flake cross-sectional sizes being 1-2 nm, an electrical conductivity of at least 3200 S^cm’¹, a fluorine percentage of up to 15 at.%, a percentage of bound forms of oxygen and hydroxyl groups of up to 20 at.% and a chlorine percentage of up to 2 at.%, wherein said MXenes are produced by chemical exfoliation from the MAX phase (Ti₃AlC₂ ) with an HF or LiF/HCl solution.

3. Method of Claim 1 wherein said low molecular weight organic semiconductors are in the form of bathocuproine (C₂₆H₂₀N₂) or biphene (C₂₄H₁₆N₂) or nitrogen-containing counterparts for selective transport with n and p type conductivity.

4. Method of Claim 1 wherein said dehydrated organic solvents are in the form of alcohol solvents of at least 99% purity, e.g. methanol or ethanol or isopropanol.

5. Method of Claim 1 wherein dispersion of MXenes Ti₃C₂T_x is accomplished with permanent stirring for 24 h and preliminary ultrasonication for 1 h.

6. Method of Claim 1 wherein said liquid phase method of buffer layer synthesis on said selectively transporting layer having the n type conductivity is implemented by printing, spraying or centrifugation.