PEDOT: X: PSS hole transport layer material and preparation method and application thereof

Abstract

The invention relates to the field of organic solar cells, in particular to a PEDOT: X: PSS hole transport layer material and a preparation method and application thereof. The PEDOT: X: PSS hole transport layer material comprises the following raw materials: 3, 4-ethylenedioxythiophene (EDOT), polystyrolsulfon acid (PSS) and a small molecule X, the method is characterized in that two ends of a small molecule X are sulfonic acid-containing groups; the small molecules X are uniformly loaded in the PEDOT: PSS. The small molecule X with the disulfonic acid group has a multi-stage collaborative optimization mechanism, the small molecule X is wrapped in PEDOT: PSS through EDOT in-situ polymerization, and the photoelectric conversion efficiency of the organic solar cell is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of organic solar cells, specifically to a PEDOT:X:PSS hole transport layer material, its preparation method, and its application. Background Technology

[0002] Organic solar cells (OSCs), as a novel renewable energy conversion technology, have received widespread attention in recent years. PEDOT:PSS, a widely used hole transport layer (HTL) material, possesses advantages such as high conductivity, good optical transparency, solution processability, and environmental stability. It exhibits high transparency in the visible light range, allowing more light to pass through, enabling the active layer to fully absorb sunlight and improve the cell's light utilization efficiency. While maintaining high transparency, it also effectively enhances hole mobility. It can be fabricated into thin films using simple processes such as solution spin coating, exhibiting excellent film-forming properties and facilitating large-scale production and processing.

[0003] Currently, commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS AI 4083) is one of the most widely used high-performance liquid transport (HTL) materials in organic solar cells (OSCs). Heraeus GmbH in Germany produces the Clevios™ series, which is the world's most well-known and widely used PEDOT:PSS brand. However, while commercially available PEDOT:PSS offers standardized performance, its high price and proprietary formulation limitations hinder its application in large-scale, low-cost electronic devices and in-depth mechanistic research. Although PEDOT:PSS is currently the preferred material for hole transport layers in organic solar cells due to its properties, it also has some drawbacks, such as hygroscopicity, phase separation issues, and compatibility with the active layer, which require further optimization. For example, it easily absorbs moisture from the air, which causes changes in the conductivity and properties of the film, affecting the stability and performance of the battery. During the film preparation process, phase separation easily occurs between PEDOT and PSS. The PEDOT enriched region (~10nm) and the PSS insulating phase (~5nm) form a conductive network with a limited percolation threshold, forming an uneven microstructure that affects the conductivity and interface properties of the film.

[0004] In organic solar cells, introducing a third component into PEDOT:PSS has been shown to affect the performance of the thin film, thereby altering the device's performance. Patent CN116761449A discloses the introduction of amine hydrochloride into the hole transport layer. Amino ions can react with excess sulfonic acid groups in PEDOT:PSS, effectively regulating the pH of the PEDOT:PSS aqueous solution and reducing its probability of corroding the ITO anode. Simultaneously, the amine compounds can form hydrogen bonds with PEDOT:PSS, inducing a more ordered stacking pattern, resulting in a more uniform morphology of the hole transport layer, more efficient charge transport, and significantly reduced charge recombination. CN111276623A discloses the addition of molybdenum trioxide to the hole transport layer; the far-field effect of the metal nanoparticles effectively improves the photoluminescence efficiency of the blue perovskite emitting layer. CN111129313A's composite hole transport material incorporates ammonium metavanadate, which can effectively increase the open-circuit voltage of the battery device, thereby improving the battery's conversion efficiency.

[0005] However, the introduction of a third component into the PEDOT:PSS binary system often leads to phase separation or sedimentation in the solution due to interactions and compatibility issues among the multiple components, thereby affecting the homogeneity, reproducibility, and subsequent processing performance of the material. The main reason is the lack of synthetic strategies and component control, resulting in decreased colloidal stability in the ternary PEDOT-based composite solution, leading to significant sedimentation or aggregation after long-term standing. This characteristic can be attributed to the introduction of the third component disrupting the synergistic effect between PEDOT and PSS segments, weakening the system's charge balance and steric hindrance, thus exacerbating particle aggregation and deposition. Summary of the Invention

[0006] To address the aforementioned drawbacks of using PEDOT:PSS as a hole transport layer material in existing organic solar cells, this invention proposes a PEDOT:X:PSS hole transport layer material, its preparation method, and its applications. X is a small molecule with sulfonic acid groups at both ends, achieving precise control of the PEDOT conductive domains through an "anchoring-bridging" effect. The sulfonic acid groups at both ends form strong hydrogen bonds with PSS segments, while the rigid conjugated framework in the middle induces the PEDOT chains to align orderly along the crystal plane. This dual-site synergistic effect effectively reduces the π-π stacking distance and significantly improves hole mobility. Ultimately, this significantly improves the photoelectric conversion efficiency (PCE) of organic solar cells. Specifically, this invention provides the following technical solutions to address the above-mentioned technical problems:

[0007] A PEDOT:X:PSS hole transport layer material comprises the following raw materials: 3,4-ethylenedioxythiophene (EDOT), polystyrene sulfonic acid (PSS), and small molecule X; the two ends of small molecule X are sulfonic acid groups; small molecule X is uniformly loaded in PEDOT:PSS.

[0008] Further, the molar ratio of 3,4-ethylenedioxythiophene, styrene sulfonic acid and small molecule X is 4-8:0.8-1.2:0.8-1.2, preferably 4-6:0.8-1:0.8-1; the molar amount of styrene sulfonic acid is obtained by dividing the mass of the polymer polystyrene sulfonic acid by the molar mass of the monomer styrene sulfonic acid.

[0009] Furthermore, the sulfonic acid group is selected from at least one of sulfonic acid group, sodium sulfonate, potassium sulfonate, and ammonium sulfonate.

[0010] Further, the small molecule X is selected from at least one of 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid or its salt, biphenyl-4,4'-disulfonic acid or its salt. For example, sodium 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid (SDCDPS) and biphenyl-4,4'-disulfonic acid (BPDSA).

[0011] This invention proposes introducing a third component, a small molecule X, into PEDOT:PSS. The small molecule X has sulfonate groups at both ends. The bissulfonic acid groups form strong hydrogen bonds with the PSS chain segments, while the rigid conjugated backbone induces the PEDOT chains to align orderly along the crystal planes. This dual-site synergistic effect effectively reduces the π-π stacking distance and significantly improves hole mobility. At the mesoscale, the bipolar molecule forms a three-dimensional through-network through dynamic self-assembly, with its sulfonic acid end groups forming chemically bonded interfaces with the ITO substrate, simultaneously achieving work function regulation and strong interfacial dipoles, thus improving energy level matching. Furthermore, the "bipolar doping" mechanism induced by the symmetric molecular structure creates a gradient doping distribution at the PEDOT domain boundaries, achieving directional hole transport by constructing a carrier concentration gradient field, thus reducing the interfacial recombination rate. In contrast, the unipolar molecule is only anchored to PSS through a single hydrogen bond formed by its terminal sulfonic acid group, resulting in an anisotropic and disordered molecular orientation. Its rigid conjugated core, lacking symmetric anchoring points, undergoes intra-chain distortion, weakening the π-π orbital overlap efficiency. Secondly, at the mesoscopic phase level, the single-end anchoring mechanism induces a "pseudo-Janus interface" effect: the sulfonic acid end selectively adsorbs into the PSS phase region while the hydrophobic end is exposed on the PEDOT domain surface, causing local phase separation and forming a carrier transport barrier. In summary, molecules with bissulfonic acid groups possess a multi-level synergistic optimization mechanism, providing a new technical path for designing high-performance composite hole transport materials. The inventors also attempted with small molecules containing a sulfonate salt, but found that the aforementioned technical effects were not achieved.

[0012] Furthermore, the introduction of a small molecule X with two sulfonate end groups into the hole transport layer material of PEDOT:PSS to enhance photoelectric performance requires in-situ oxidative polymerization of EDOT. Introducing a small molecule X with two sulfonate end groups into already polymerized PEDOT:PSS material will not successfully improve photoelectric performance. The polymerization methods of EDOT are well-known in the field. Chemical oxidative polymerization is the most common and suitable method for large-scale production. The oxidant strips electrons from EDOT, generating cationic free radicals, which then couple and dehydrogenate to form conjugated polymer chains. Electrochemical polymerization involves dissolving EDOT monomers in a solvent containing a supporting electrolyte (such as LiClO4). A conductive substrate (such as ITO glass, platinum, or gold) is used as the working electrode, and a voltage higher than the EDOT oxidation potential is applied. Monomers are oxidized on the surface of the working electrode, forming an insoluble PEDOT film deposited on the electrode. Transition metal-catalyzed coupling polymerization utilizes transition metal catalysts such as palladium to induce coupling reactions in halogenated or tin-alkylated EDOT derivatives (e.g., Stille coupling, Suzuki coupling, direct arylation polymerization). Interfacial polymerization involves dissolving the EDOT monomer and oxidant in two immiscible solvents (e.g., organic phase / aqueous phase). The polymerization reaction occurs at the interface between the two phases, and the resulting PEDOT film self-assembles at the interface. In one specific embodiment of the invention, EDOT is oxidatively polymerized in the presence of persulfate and trifluoromethanesulfonate to obtain PEDOT.

[0013] The second objective of this invention is to provide a method for preparing the above-mentioned PEDOT:X:PSS hole transport layer material, comprising the following steps:

[0014] (S1) Polystyrene sulfonic acid (PSS), catalyst and oxidant were prepared as a precursor solution, and small molecule X and 3,4-ethylenedioxythiophene (EDOT) were added. After the reaction was completed, the mixture was dialyzed to remove impurities and a PEDOT:X:PSS dispersion was obtained.

[0015] (S2) The dispersion is coated on the substrate and annealed to obtain the PEDOT:X:PSS hole transport layer material.

[0016] Further, in step (S1), the oxidant is a persulfate, such as at least one of sodium persulfate, potassium persulfate, and ammonium persulfate; the catalyst is a trifluoromethanesulfonate, such as at least one of ferric trifluoromethanesulfonate and scandium trifluoromethanesulfonate. The amount of catalyst used is 15-25% of the mass of EDOT, and the amount of oxidant used is 150-250% of the mass of EDOT. The reaction is allowed to proceed completely at room temperature for 20-30 hours. Dialysis to remove impurities involves dialyzing the crude product with deionized water for 10-15 hours using a dialysis membrane with a molecular weight cutoff of 500-1000 Da.

[0017] Further, in step (S1), the molar ratio of polystyrene sulfonic acid, EDOT, and small molecule X satisfies the following condition: the molar ratio of polystyrene sulfonic acid, EDOT, and small molecule X is 4-8:0.8-1.2:0.8-1.2, preferably 4-6:0.8-1:0.8-1. The molar amount of polystyrene sulfonic acid is obtained by dividing the mass of polystyrene sulfonic acid by its molecular weight.

[0018] Furthermore, in step (S2), the substrate is not particularly limited, such as an anodic substrate (ITO); the coating method is not particularly limited, such as spin coating, with a spin coating speed of 2000-4000 rpm. The annealing treatment is performed at 110-140℃ for 5-30 min, preferably at 120-135℃ for 10-20 min.

[0019] A third objective of this invention is to provide the use of the above-mentioned PEDOT:X:PSS hole transport layer material as a hole transport layer in organic solar cells.

[0020] The introduction of small molecule X as a third component into the PEDOT:PSS system significantly enhances its photoelectric efficiency as a hole transport layer material. Small molecule X may partially replace the doping effect of PSS, reducing Coulomb repulsion between PEDOT chains through more efficient charge compensation, promoting polaron delocalization, and forming ordered but moderately dispersed conductive pathways in the PEDOT chains, thus improving conductivity. The addition of small molecule X lowers the surface energy and makes the film morphology smoother. This synergistic optimization increases interfacial contact, and the smoother surface provides a more uniform electric field distribution, which is beneficial for the ordered transport of holes. Simultaneously, the low roughness also facilitates good contact with the active layer, forming a tight heterojunction interface, reducing defect states at the interface, and improving charge transfer efficiency at the interface. The disulfonic acid groups of small molecule X, through strong hydrogen bonds or ionic interactions, may partially neutralize the negative charge of PSS, reducing its electrostatic binding to PEDOT, causing the PEDOT chains to transform from a coiled, coiled shape to a more extended fibrous conformation, thereby forming more continuous conductive pathways and significantly improving conductivity.

[0021] The fourth objective of this invention is to provide an organic solar cell whose hole transport layer is the aforementioned PEDOT:X:PSS hole transport layer material.

[0022] Furthermore, the organic solar cell includes the following components from bottom to top: an anode substrate, a hole transport layer, an organic active layer, an electron transport layer, and a cathode layer.

[0023] As a preferred embodiment of the above technical solution, the anode substrate is indium tin oxide glass, i.e., ITO; the organic active layer is poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alternating-(5,5-(1',3'-bis-2-thiophene-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene] -4,8-dione))]:2,2'-[[12,13-bis(2-ethylhexyl)-12,13-dihydro-3,9-bisundecylbisthieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-e:2',3'-g][2,1,3]benzothiadiazole-2,10-diyl]bis[methylene(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diylidene)] ] bis[malononitrile], or poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alternating-(5,5-(1',3'-bis-2-thiophene-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione))]: 2,2'-[[12,13-bis(2-butyloctyl)] 12,13-dihydro-3,9-dinonylbisthiopheno[2'',3'':4',5']thiopheno[2',3':4,5]pyrrolo[3,2-e:2',3'-g][2,1,3]benzothiadiazole-2,10-diyl]bis[methylene(5,6-chloro-3-oxo-1H-indene-2,1(3H)-diyl)]]bis[malononitrile], i.e. PM6:Y6, with an organic active layer thickness of 90-120 nm;

[0024] The electron transport layer is N,N-bis[7-(dimethylamino)-4-azaheptyl]-3,4,9,10-perylenetetracarboxydiimide, i.e., PDINN, with a thickness of 10-30 nm; the cathode layer is Ag with a thickness of 80-100 nm.

[0025] As a preferred embodiment of the above technical solution, the process of treating the surface of the anode layer of the anode substrate includes: sequentially ultrasonically cleaning the ITO glass with detergent, deionized water, acetone, and anhydrous ethanol for a period of time; drying it with nitrogen gas, and then performing surface plasma treatment on the surface of the anode substrate.

[0026] Compared with the prior art, the present invention achieves the following beneficial effects:

[0027] By introducing small molecules SDCDPS and BPDSA with sulfonic acid groups at both ends into the PEDOT:PSS system via oxidative polymerization with EDOT to construct a ternary composite hole transport layer, the performance of this layer differs significantly from that of traditional commercial PEDOT:PSS (Al4083) and directly doping small molecules into Al4083. The bissulfonic acid functionalized small molecules effectively improve the overall performance of the PEDOT:PSS-based hole transport layer, increasing the device's photoelectric conversion efficiency by approximately 2% compared to pure PEDOT:PSS. This reveals that the sulfonic acid groups at both ends form a more continuous three-dimensional conductive network through strong electrostatic interactions with PSS segments, while their planar rigid structure effectively improves the carrier mobility of the composite. This technology demonstrates the crucial role of molecular structure design: sulfonic acid groups, as functional groups, can optimize the doping mechanism of conductive polymers, providing a new molecular engineering strategy for designing ternary hole transport materials. Attached Figure Description

[0028] Figure 1 These are atomic force microscope images of hole transport layer materials prepared by different methods.

[0029] Figure 2 These are the JV curves of Example 1, Example 2, Comparative Example 7, and Comparative Example 8. Detailed Implementation

[0030] The technical solution of the present invention will be further explained and illustrated below with reference to specific embodiments.

[0031] Example 1

[0032] Step 1: First, Fe(OTf)3 (0.01g), Na2S2O8 (0.098g), disodium 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid (SDCDPS) (0.182g, 0.371mmol), and PSS (1.367g, 2.226mmol, PSS molar amount based on monomer) (PSS is a 30% aqueous solution) were sequentially added to a beaker containing 10ml of deionized water and stirred for 30 minutes. Then, EDOT (0.045g, 0.371mmol) was added. After stirring at room temperature for 24 hours, the solution changed from yellow to dark blue, indicating successful polymerization. The crude product was dialyzed against deionized water for 12 hours using a dialysis membrane to obtain a PEDOT:SDCDPS:PSS dispersion.

[0033] Step 2, cleaning the anode substrate (ITO) includes: ultrasonically cleaning the ITO glass for 20 minutes each with detergent, deionized water, acetone, and anhydrous ethanol in sequence, and then setting it aside for use.

[0034] Step 3: Dry the anode substrate with nitrogen gas, and then clean the residual organic matter on the ITO surface with plasma generated by the Plasma cleaner for 6 minutes, while increasing the wettability of the ITO substrate surface.

[0035] Step 4: Spin-coat PEDOT:PSS onto the ITO anode substrate at 3500 rpm for 40 seconds. Then anneal the spin-coated anode substrate at 135°C for 10 minutes.

[0036] Step 5: The active layer of the organic solar cell uses the most typical PM6:Y6 system, with a mass ratio of 1:1.2. The solvent used is ultra-dry chloroform, with a total concentration of 15.4 mg / ml. The prepared solution is stirred at 45°C for 6 hours, and then spin-coated onto the PEDOT:PSS layer at a speed of 3000 rpm.

[0037] Step 6: The electron transport layer is prepared by dissolving PDINN in a methanol solution with a concentration of 1.0 mg / mL, and then spin-coating it onto the active layer PM6:Y6 at a speed of 3000 rpm for 40 seconds to obtain the electron transport layer.

[0038] Step 7: The metal cathode Ag is placed under the photomask at 10 -4 Organic solar cells are obtained by physical vapor deposition in a vacuum of Pa.

[0039] Example 2

[0040] The other conditions are the same as in Example 1, except that in step 1, 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium (SDCDPS) is replaced with an equimolar amount of biphenyl-4,4'-disulfonic acid (BPDSA).

[0041] Comparative Example 1

[0042] The assembly of the solar cell is basically the same as in Example 1, except that the hole transport layer uses commercially available PEDOT:PSS, model Al4083, purchased from Xi'an Polymer Optoelectronics Technology Co., Ltd. The steps are as follows:

[0043] Step 1, cleaning the anode substrate (ITO) includes: ultrasonically cleaning the ITO glass for 20 minutes each with detergent, deionized water, acetone, and anhydrous ethanol in sequence, and then setting it aside for use.

[0044] Step 2: Dry the anode substrate with nitrogen gas, and then use plasma generated by a plasma cleaner to clean the residual organic matter on the ITO surface for 6 minutes, while increasing the wettability of the ITO substrate surface.

[0045] Step 3: After filtering the PEDOT:PSS (4083) solution through a filter with a pore size of 0.45 micrometers, spin-coat the PEDOT:PSS onto the ITO anode substrate at a speed of 3500 rpm for 40 seconds. Then, anneal the spin-coated anode substrate at 135°C for 10 minutes.

[0046] Step 4: The active layer of the organic solar cell uses the most typical PM6:Y6 system, with a mass ratio of 1:1.2. The solvent used is ultra-dry chloroform, with a total concentration of 15.4 mg / ml. The prepared solution is stirred at 45°C for 6 hours, and then spin-coated onto the PEDOT:PSS layer at a speed of 3000 rpm.

[0047] Step 5: The electron transport layer is prepared by dissolving PDINN in a methanol solution with a concentration of 1.0 mg / mL, and then spin-coating it onto the active layer PM6:Y6 at a speed of 3000 rpm for 40 seconds to obtain the electron transport layer.

[0048] Step 6: The metal cathode Ag is placed under the photomask at 10 -4 Organic solar cells are obtained by physical vapor deposition in a vacuum of Pa.

[0049] Comparative Example 2

[0050] The other conditions and operations are the same as in Example 1, except that in step 1, 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium salt is not added.

[0051] Comparative Example 3

[0052] The other conditions and operations are the same as in Example 1, except that in step 1, 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium salt (SDCDPS) is replaced with an equimolar amount of sodium dodecylbenzenesulfonate (SDBS).

[0053] Comparative Example 4

[0054] The other conditions and operations are the same as in Example 1, except that in step 1, 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium (SDCDPS) is replaced with an equimolar amount of diphenylamine sulfonate sodium (PDS).

[0055] Comparative Example 5

[0056] The other conditions and operations are the same as in Example 1, except that in step 1, 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium (SDCDPS) is replaced with an equimolar amount of taurine (TA).

[0057] Comparative Example 6

[0058] Other conditions and procedures were the same as in Comparative Example 1, except that 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid disodium salt (SDCDPS) was added directly to PEDOT:PSS (4083), with 10 ml of PEDOT:PSS (4083) and 0.182 g of SDCDPS.

[0059] Comparative Example 7

[0060] Other conditions and procedures are the same as those in Comparative Example 1. The difference is that biphenyl-4,4'-disulfonic acid (BPDSA) is added directly to PEDOT:PSS (4083), where 10 ml of PEDOT:PSS (4083) and an equal molar amount of SDCDPS are used.

[0061] Figure 1 These are atomic force micrographs of hole transport layer materials prepared by different methods. It can be seen that the roughness of the materials synthesized in Example 1 and Example 2 is smaller than that in Comparative Example 1 and Comparative Example 2.

[0062] Application examples

[0063] The performance of the organic solar cells in the above embodiments and comparative examples was tested, and the results are shown in Table 1 below. This patent uses a Keithley 2400 source meter to measure the current density-voltage (JV) characteristics of the organic solar cells. The experiment was conducted under standard solar irradiance conditions of 100 mW / cm² AM 1.5G, with an Enlitech SS-F5-3A solar simulator as the irradiance source. To ensure the accuracy of the irradiance intensity, a monocrystalline silicon reference cell (Enlitech SRC-00207) was used for calibration. During the measurement, the device was directly placed under 100 mW / cm² illumination conditions, and JV characteristics were tested at a scan rate of 120 mV / s using zero pre-bias conditions. All measurements were performed in a nitrogen atmosphere glove box to avoid the influence of environmental factors on the test results.

[0064] Figure 2 The JV curves of Examples 1, 2, 7, and 8 show that directly doping small molecule X into commercially available PEDOT:PSS does not yield ideal results, especially in Comparative Example 7, where the PCE is only 2.99%.

[0065] Table 1 Performance Tests of Organic Solar Cells

[0066]

[0067] This invention significantly improves the power conversion efficiency (PCE) of organic solar cells by doping a small molecule X with sulfonic acid groups at both ends into the hole transport layer material of PEDOT:X:PSS. The inventors also discovered that this doping strategy requires in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT) to coat and dope the small molecule X. Directly doping the small molecule X into PEDOT:PSS does not achieve the goal of improving the PCE of organic solar cells.

Claims

1. A PEDOT:X:PSS hole transport layer material, comprising the following raw materials: 3,4-ethylenedioxythiophene (EDOT), polystyrene sulfonic acid (PSS), and small molecule X; characterized in that, Small molecule X has sulfonic acid groups at both ends; small molecule X is uniformly loaded in PEDOT:PSS.

2. The hole transport layer material according to claim 1, characterized in that, The molar ratio of 3,4-ethylenedioxythiophene, styrene sulfonic acid, and small molecule X is 4-8:0.8-1.2:0.8-1.2, preferably 4-6:0.8-1:0.8-1; the molar amount of styrene sulfonic acid is obtained by dividing the mass of the polymer polystyrene sulfonic acid by the molar mass of the monomer styrene sulfonic acid.

3. The hole transport layer material according to claim 1, characterized in that, The sulfonic acid group is selected from at least one of sulfonic acid group, sodium sulfonate, potassium sulfonate, and ammonium sulfonate.

4. The hole transport layer material according to claim 1, characterized in that, The small molecule X is selected from at least one of 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid or its salt, biphenyl-4,4'-disulfonic acid or its salt. For example, sodium 4,4'-dichlorodiphenyl sulfone-3,3'-disulfonic acid (SDCDPS) and biphenyl-4,4'-disulfonic acid (BPDSA).

5. The method for preparing the PEDOT:X:PSS hole transport layer material according to any one of claims 1-4, characterized in that, Includes the following steps: (S1) Polystyrene sulfonic acid (PSS), catalyst and oxidant were prepared as a precursor solution, small molecule X and 3,4-ethylenedioxythiophene (EDOT) were added, polymerization reaction was carried out, and impurities were removed by dialysis to obtain PEDOT:X:PSS dispersion; (S2) The dispersion is coated on the substrate and annealed to obtain the PEDOT:X:PSS hole transport layer material.

6. The preparation method according to claim 5, characterized in that, In step (S1), the oxidant is a persulfate, such as at least one of sodium persulfate, potassium persulfate, and ammonium persulfate; the catalyst is a trifluoromethanesulfonate, such as at least one of ferric trifluoromethanesulfonate and scandium trifluoromethanesulfonate; further, the amount of catalyst is 15-25% of the mass of EDOT, and the amount of oxidant is 150-250% of the mass of EDOT; even further, the polymerization reaction is carried out at room temperature for 20-30 hours; dialysis to remove impurities involves dialysis the crude product with deionized water for 10-15 hours using a dialysis membrane with a molecular weight cutoff of 500-1000 Da.

7. The preparation method according to claim 5, characterized in that, In step (S1), the polystyrene sulfonic acid, EDOT, and small molecule X are in the following molar ratio: the molar ratio of polystyrene sulfonic acid, EDOT, and small molecule X is 4-8:0.8-1.2:0.8-1.2, preferably 4-6:0.8-1:0.8-1; and / or, in step (S2), the substrate is an anodic substrate (ITO); the coating is spin coating; preferably, the spin coating speed is 2000-4000 rpm; the annealing treatment is performed at 110-140℃ for 5-30 min, preferably at 120-135℃ for 10-20 min.

8. Use of the PEDOT:X:PSS hole transport layer material according to any one of claims 1-4 as a hole transport layer in an organic solar cell.

9. An organic solar cell, characterized in that, Its hole transport layer is the PEDOT:X:PSS hole transport layer material as described in any one of claims 1-4.

10. The organic solar cell according to claim 9, characterized in that, The organic solar cell comprises, from bottom to top, the following components: an anode substrate, a hole transport layer, an organic active layer, an electron transport layer, and a cathode layer.

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