Conjugated molecule passivation of cadmium-free two-dimensional quantum sheets and methods of solar cell fabrication

Abstract

The application discloses a preparation method of a conjugated molecule passivated cadmium-free two-dimensional quantum sheet and solar cell, and long-chain organic ligands on the surface of CuInS2 quantum sheets without heavy metals are replaced by pyridine and its derivatives through conjugated small molecule ligand modification, so that the coordination environment of the quantum sheet surface is regulated. The modified quantum sheet no longer releases energy through fluorescence emission in the device, but transmits the absorbed light energy in the form of dark energy to the active layer of the polymer solar cell through non-radiative energy transfer and interface charge transfer, so that additional light energy gain is realized. Meanwhile, the ligand regulation can improve the interface matching between the quantum sheet and the organic active layer, optimize the active layer morphology, promote the carrier transmission and reduce the recombination loss. The application realizes the synergistic improvement of light absorption and energy utilization efficiency without introducing toxic heavy metals, so that the photoelectric conversion performance of the polymer solar cell is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a conjugated molecular passivated cadmium-free two-dimensional quantum sheet and its preparation method, as well as its method and application for improving the efficiency of polymer solar cells through dark energy conversion. Background Technology

[0002] Quantum dots are a class of semiconductor nanomaterials exhibiting quantum size effects, but their limitations in optimizing optical and electrical properties and environmental safety restrict their application in optoelectronic devices. Therefore, quantum sheets with two-dimensional structures have gradually attracted attention. These sheets possess quantum confinement effects in the thickness direction and a continuous lattice structure in the in-plane direction, which is beneficial for carrier transport and has potential application value in optoelectronic devices. In existing technologies, quantum sheets are typically prepared using solution methods, relying on ligands to control their growth and surface state. Commonly used ligands are long-chain organic molecules such as oleylamine and oleic acid. While these ligands can improve material dispersion and control structure, their insulating properties can hinder charge transport between quantum sheets. Furthermore, they have poor compatibility with organic active layers, easily introducing interface defects, thus limiting device performance improvement.

[0003] Furthermore, while bulk heterojunction structures based on donor / acceptor structures in polymer solar cells can achieve effective separation of photogenerated excitons, they still suffer from limited light absorption range, restricted charge carrier transport, and significant recombination losses. Existing methods of modification by introducing functional materials struggle to simultaneously achieve both interface matching and charge transport performance.

[0004] Therefore, how to rationally select and regulate the surface ligand system while ensuring the stability of the quantum sheet structure, reduce the adverse effects of ligands on charge transport, and improve the interface matching between the quantum sheet and the organic active layer, thereby improving the overall performance of the device, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention aims to address the problems of charge transport obstruction and poor interface matching caused by long-chain ligands on the surface of cadmium-free quantum sheets in the prior art. It proposes a method to improve the efficiency of polymer solar cells through dark conversion of light energy using cadmium-free quantum sheets. This method modifies the surface of the quantum sheet by introducing conjugated molecules, thereby reducing the insulating barrier effect of organic ligands, improving the interfacial contact state between the quantum sheet and the polymer active layer, and optimizing the microstructure and carrier transport path of the active layer, thereby reducing recombination loss and improving device performance.

[0006] The present invention adopts the following technical solution: A method for preparing a conjugated molecular passivated cadmium-free two-dimensional quantum sheet includes the following steps: (1) Dissolve InCl3·4H2O in octadecene solvent and oleylamine ligand solution by heating and completely remove oxygen to obtain indium source solution; dissolve sulfur powder completely in octadecene and add it to indium source solution, mix to remove oxygen, and heat. (2) Heat the mixed solution obtained in step (1) to a certain temperature, maintain the reaction under nitrogen atmosphere, add the dissolved copper source solution, react for a certain time, cool down to room temperature, add excess methanol and centrifuge to obtain the hexagonal CuInS2 two-dimensional quantum sheet modified with oleylamine ligand. (3) Dissolve CuInS2 quantum sheets in toluene / chloroform solution, add an appropriate amount of nitrogen-containing heteroatom aromatic compound solution, and completely remove oxygen under nitrogen protection gas conditions; (4) Add reflux conditions to the solution in step (3), heat and stir, react at an appropriate temperature for a period of time, then stop heating and cool the solution to room temperature; (5) Add hexane, trichloroethylene, dichloromethane or a mixture of two of these solvents to the solution in step (4), centrifuge, and repeat three times to obtain conjugated molecular passivated hexagonal CuInS2 quantum sheets.

[0007] In step (1), the proportions of substances used are as follows: InCl3·4H2O is 0.15 to 0.3 mmol, and sulfur powder is 0.15 to 0.3 mmol; the heating range is 100 ℃ to 120 ℃ to ensure complete dissolution and no solid impurities remain. In step (2), the copper source solution is: 0.15-0.3 mmol of CuI is dissolved in 1-3 ml of n-dodecyl mercaptan; when the mixed solution is heated to 160-180 °C, the Cu source solution is injected, the reaction time is 5-15 min, and then the temperature is lowered to room temperature.

[0008] In step (3), the nitrogen-containing heteroatom aromatic compound is selected from the monodentate ligand pyridine molecule; the volume ratio of quantum sheet to toluene solution to pyridine solution is 1:3 to 1:6, the reaction temperature is 60 ℃, the centrifugation rate is 10000 to 12000 r / min, and the centrifugation time is 8 to 15 min; the concentration of quantum sheet solution is 20 mg / ml, and the mass fraction of pyridine solution is 99.5%.

[0009] In step (4), the heating temperature of the mixed solution is 60~80 ℃, and the reaction time is 1~2 h.

[0010] CuInS2 quantum sheets with conjugated molecules were prepared according to the above method.

[0011] The present invention also provides a method for selecting nitrogen-containing heteroatom aromatic compounds, comprising the following steps: (1) Select nitrogen-containing heteroatom-containing small molecules with aromatic conjugated structures as candidate ligands; (2) Based on the number of coordination sites, molecular size and steric hindrance of the ligand molecule, candidate ligands are screened, and nitrogen-containing ligands with monodentate, simple molecular structure and small steric hindrance are preferred. Based on the above method, pyridine conjugated small molecules were selected as ligands for surface modification of quantum sheets.

[0012] This invention also provides a method for preparing a CuInS2 quantum sheet-enhanced polymer solar cell, using the above-mentioned pyridine-passivated CuInS2 quantum sheet, comprising the following steps: (1) A hole transport layer was prepared on a conductive ITO glass substrate by spin coating at a spin coating rate of 3500 r / min to 5000 r / min for 30 to 50 s; and then heat-treated at 150 °C for 15 min. (2) The chloroform solution of the pyridine passivated CuInS2 quantum sheet was mixed with the active layer solution for doping. The liquid volume doping ratio was 0.5%~3%, and the mixed solution was heated and stirred for 3~4 h.

[0013] (3) Using spin coating, PM6:Y6:NPLs active layer solution is spin coated on hole transport layer film at a spin coating rate of 2000~3500 r / min for 30~60 s, followed by heat treatment at 100 ℃ for 10~15 min. (4) Spin-coating an electron transport layer at a spin rate of 3000~4000 r / min for 40~60 s.

[0014] (5) A metal electrode is deposited on the surface of the electron transport layer by vacuum deposition.

[0015] The materials of the hole transport layer include, but are not limited to, PEDOT:PSS, PTAA, NiO, MoO3, etc.

[0016] The active layer material includes, but is not limited to, PM6:IT-4F, PM6:Y6, PM6:L8-BO, PM6:D18, etc.

[0017] The electron transport layer includes, but is not limited to, PDIN, PDINO, NDI-N, PFN-Br, etc.

[0018] The electrodes include, but are not limited to, Al, Au, Mn, Zn, etc.

[0019] The hole transport layer has a thickness of 50–150 nm; the active layer film has a thickness of 150–200 nm; the electron transport layer has a thickness of 30–50 nm; and the electrode has a thickness of 100–150 nm.

[0020] CuInS2 quantum sheet polymer solar cells were obtained according to the above preparation method.

[0021] Using the above scheme, this invention converts the long-chain organic ligands in the preparation of quantum sheets into nitrogen-containing heteroatom aromatic compounds, improving the solubility of the quantum sheets and their dispersibility in the active layer of polymer solar cells. By modifying CuInS2 quantum sheets without heavy metals with conjugated small-molecule ligands, the long-chain organic ligands on their surface are replaced with pyridine and its derivatives, thereby regulating the coordination environment on the quantum sheet surface. The modified quantum sheets no longer release energy through fluorescence emission in the device, but instead transfer the absorbed light energy to the active layer of the polymer solar cell as dark energy through non-radiative energy transfer and interfacial charge transfer pathways, achieving additional light energy gain. Simultaneously, the ligand regulation improves the interfacial matching between the quantum sheet and the organic active layer, optimizes the morphology of the active layer, promotes carrier transport, and reduces recombination losses. This invention also provides corresponding device structures and preparation methods, improving device performance. The light absorption capability at 420 nm wavelength is enhanced, and the device's photoelectric conversion efficiency, fill factor, and charge collection efficiency are increased from 14.12%, 74%, and 86.3% to 15.8%, 78%, and 88.39%, respectively. Compared with existing technologies, this invention achieves a synergistic improvement in light absorption and energy utilization efficiency without introducing toxic heavy metals, thereby effectively improving the photoelectric conversion performance of polymer solar cells. Attached Figure Description

[0022] Figure 1 The ultraviolet absorption spectra of CuInS2 quantum sheets prepared in Example 1 of this invention at different synthesis stages are shown.

[0023] Figure 2 Transmission electron microscopy (TEM) image of CuInS2 quantum sheets prepared in Example 1 of this invention.

[0024] Figure 3 The nitrogen-containing heteroatom aromatic compound selected in Example 2 of this invention.

[0025] Figure 4 This is a schematic diagram of the photoluminescence spectrum and quantum yield before and after ligand exchange in Example 2 of the present invention.

[0026] Figure 5 This is a comparison of the Fourier transform of the quantum sheet before and after ligand exchange in Example 2 of the present invention.

[0027] Figure 6 (ae) are schematic diagrams of the STEM morphology of the quantum sheet after ligand exchange in Example 2 of the present invention and the mapping distribution of Cu, In, S and N elements.

[0028] Figure 7 This is a schematic diagram of the ultraviolet absorption spectrum of the active layer film in Example 3 of the present invention.

[0029] Figure 8 This is a schematic diagram comparing the energy levels of each component in the active layer of Example 3 of the present invention.

[0030] Figure 9 (ab) are schematic diagrams showing the contact angles between the active layer film and water and ethylene glycol solutions before and after the doped quantum sheet in Example 3 of the present invention.

[0031] Figure 10 This is a transmission electron microscope (TEM) schematic diagram of the active layer thin film in Embodiment 3 of the present invention.

[0032] Figure 11 This is a schematic diagram of the active layer in Embodiment 3 of the present invention using an atomic force microscope.

[0033] Figure 12 The image shows the JV photoelectric efficiency of the solar cell prepared in Example 3 of this invention.

[0034] Figure 13 This is a schematic diagram of the polymer solar cell device prepared in Example 3 of the present invention. Detailed Implementation

[0035] The present invention will be described in detail below with reference to specific embodiments. Unless otherwise specified, all methods are conventional; the reagents and materials mentioned are commercially available unless otherwise specified.

[0036] Example 1: Preparation method of conjugated molecule passivated CuInS2 quantum sheet: (1) Add 0.17 mmol of InCl3·4H2O to a three-necked flask, add 6 ml of octadecene and 6 ml of oleylamine; heat to 100 °C to ensure that the mixed solution is completely dissolved as an indium source solution; add 0.25 mmol of sulfur powder and 3 ml of octadecene to a test tube, heat the test tube with an alcohol lamp until the sulfur is completely dissolved, and pass nitrogen protective gas into the test tube during heating to prevent oxidation; then add the sulfur source solution in the test tube to the indium source solution, immediately switch the apparatus to vacuum state, maintain this state and heat to 100 °C, repeat the operation 3~4 times by charging N2 for 2 min and vacuuming for 3 min, the heating rate is 5 °C / min, and the reaction time is 15~30 min; (2) Heat the mixed solution from step (1) to 160 °C, dissolve 0.19 mmol of CuI in 2 ml of n-dodecyl mercaptan, quickly inject it into a three-necked flask, react for 10 min, cool to room temperature, add excess methanol, and centrifuge at 12000 r / min for 10 min to obtain CuInS2 quantum sheets modified with oleylamine ligands.

[0037] (3) Take the quantum sheet from step (2) and dissolve it completely in toluene solution. Transfer it to a 50 ml three-necked flask, seal it with a glass sleeve and adapter, stir the solution, and slowly add 20 ml of 99.5% pyridine solution using a syringe. As the injected content increases, the stirring speed is slowly increased. Degas under nitrogen protection for 20 min to ensure complete deoxygenation. (4) The apparatus in step (3) is refluxed to prevent excessive evaporation of the solution. The mixed solution is heated to 60°C and stirred for 1 h. After the solution naturally cools to room temperature, hexane solution is added as a precipitant and centrifuged at 10000 rpm / min for 10 min. The above operation is repeated three times to obtain pyridine passivated hexagonal CuInS2 quantum sheets.

[0038] In this invention, CuInS2 quantum sheets with conjugated molecular surface passivation are obtained by depressurized reflux ligand exchange method. Figure 1 The image shows the ultraviolet absorption spectrum of the prepared CuInS2 quantum sheet. Figure 2 The transmission electron microscope image shows the morphology of the quantum sheet, which is a regular hexagonal thin sheet. Figure 4 The change in luminescence intensity of the quantum sheet before and after ligand exchange; Figure 5 This is a schematic diagram comparing the infrared values ​​before and after ligand exchange. After ligand exchange, the characteristic peaks of pyridine in CuInS2 quantum sheets show a significant enhancement. Figure 6 The STEM and mapping distribution of pyridine-passivated CuInS2 quantum sheets show that the quantum sheets maintain a complete framework, uniform elemental distribution, and no damage to the overall structure after ligand exchange.

[0039] Example 2: Selection method for nitrogen-containing heteroatom aromatic compounds (1) Select nitrogen-containing heteroatom-containing small molecules with aromatic conjugated structures as candidate conjugated molecules, including pyridine, quinoline, quinoline, pyrazine, triazine, bipyridine and their derivatives; (2) Screen the molecular structure characteristics of the candidate conjugated molecules in step (1), including factors such as the number of coordination sites, molecular size and steric hindrance, and prioritize the exclusion of polydentate ligands and ligands with large molecular structures to avoid the formation of a dense coordination layer on the surface of the quantum sheet. (3) Further evaluate the coordination ability and interface compatibility of the conjugated molecules screened in step (2), and select monodentate nitrogen-containing conjugated molecules with moderate coordination ability and simple structure. (4) In the preferred results of step (3), pyridine is selected as the surface modification ligand of the quantum sheet. The surface of the quantum sheet is coordinated and regulated through its single coordination site, so as to reduce the insulating effect of long chain ligands while ensuring the stability of the quantum sheet. In this embodiment of the invention, a monodentate nitrogen-containing conjugated molecule, pyridine, with moderate coordination ability and simple structure, can be obtained by selecting nitrogen-containing aromatic ligands. Figure 3 The schematic diagrams of the molecular structures of the candidate ligands clearly show that different ligands differ in molecular structure, number of coordination sites, and steric hindrance. Quinoline and acridine have larger molecular structures, making them prone to forming dense capping layers; pyrazine, triazine, and bipyridine, among other multi-site ligands, have strong coordination abilities, easily leading to surface overcoordination. In contrast, pyridine has a simple structure, low steric hindrance, and is a monodentate ligand, making it more favorable for interface modulation and carrier transport, thus it is the preferred ligand for quantum sheet surface modification.

[0040] Example 3: Fabrication method of CuInS2 quantum sheet doped polymer solar cell device (1) The donor PM6 and the acceptor Y6 were placed in a glass container at a mass ratio of 1:1.2. Chloroform was added as a solvent. An appropriate amount of CuInS2 quantum sheet chloroform solution prepared in Example 1 was taken. The doping amount of the quantum sheet solution accounted for 0%, 0.5%, and 1% of the total integral, respectively. The solution was prepared into a blend solution with a concentration of 16 mg / mL. The mixed solution was heated and stirred at 50 °C for 3-5 h.

[0041] (2) The transparent glass substrate with ITO etched was ultrasonically cleaned with isopropanol for 15 min and dried with an air gun. It was then placed in an oxygen plasma cleaner for ultraviolet ozone treatment for 5-10 min to improve the adhesion of the substrate material.

[0042] (3) Place the transparent substrate material from step (2) on a spin coater and spin coat a layer of PEDOT:PSS as a hole transport layer. The spin coating speed is 3500 r / min and the time is 40 s. After spin coating, place it on a heating table and anneal at 150℃ for 15 min.

[0043] (4) Spin-coat the blended solution prepared in step (1) onto the hole transport layer prepared in step (3) as the active layer of PM6:Y6:NPLs. The spin coating speed is 2300 r / min. After spin coating, anneal at 100 ℃ for 12 min on a heating stage.

[0044] (5) A layer of PFN-Br solution was prepared as an electron transport layer on the active layer of PM6:Y6:NPLs prepared in step (4) by spin coating. The coating speed was 3500 r / min and the spin coating time was 35 s.

[0045] (6) A 100 nm thick aluminum electrode is deposited on the surface of the electron transport layer prepared in step (5) to serve as the cathode of the device, thus obtaining a CuInS2 quantum sheet doped polymer solar cell.

[0046] In this embodiment of the invention, a polymer solar cell device doped with pyridine-passivated CuInS2 quantum sheets was prepared by controlling the coordination environment on the surface of the quantum sheet. Compared with the undoped quantum sheet device, the introduction of pyridine-passivated quantum sheets into the active layer significantly improved the light absorption intensity at 420 nm. Through additional light absorption and dark energy conversion, the light-harvesting ability of the active layer was enhanced, thereby improving the photoelectric conversion performance of the device. The dark energy conversion is mainly manifested in the fact that after absorbing light energy, the CuInS2 quantum sheet modified with pyridine ligands no longer primarily releases energy through fluorescence radiation, but instead directly transfers the excited-state energy to the PM6:Y6 active layer through non-radiative energy transfer and interface charge transfer pathways, converting the additional absorbed light energy into an effective carrier generation and separation process. Furthermore, the light absorption, contact angle, and film morphology of the active layer were characterized (e.g., Figure 7 , Figures 9-11 As shown in the figure, the results indicate that the phase separation structure of the active layer is more uniform after doping, the surface roughness is reduced, and the interfacial contact is improved, which is beneficial to the transport and collection of charge carriers and reduces recombination losses; combined with Figure 8 The energy level matching relationships shown demonstrate that the introduction of quantum sheets extends the transport paths for electrons and holes. Device performance is as follows: Figure 12 As shown, the photoelectric conversion efficiency, fill factor, and current density increased from 14.12%, 74%, and 23.135 mA / cm² to 15.8%, 78%, and 25.432 mA / cm², respectively. Further optimization of process parameters can further enhance the performance of these devices. However, when bipyridine is used as a surface ligand to modify CuInS2 quantum sheets, according to existing literature, its multidentate coordination structure and large steric hindrance easily lead to the formation of a dense coordination layer, restricting interfacial charge transport and energy transfer processes. Therefore, its device performance is typically lower than that of the pyridine passivation system.

[0047] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a conjugated molecular passivated cadmium-free two-dimensional quantum sheet, characterized in that, The steps include the following: (1) Preparation of indium source solution: Sulfur powder is completely dissolved in octadecene and added to the indium source solution, mixed to remove oxygen, and heated; (2) Heat the mixed solution obtained in step (1) to a certain temperature, maintain the reaction under nitrogen atmosphere, add copper source solution, react for a certain time, cool down to room temperature, add excess methanol and centrifuge to obtain hexagonal CuInS2 two-dimensional quantum sheet modified with oleylamine ligand. (3) Dissolve CuInS2 two-dimensional quantum sheets in toluene / chloroform solution, add an appropriate amount of nitrogen-containing heteroatom aromatic compound solution, and completely remove oxygen under nitrogen protection gas conditions; (4) The solution in step (3) is refluxed and heated and stirred. After reacting at an appropriate temperature for a period of time, the heating is stopped and the solution is cooled to room temperature. (5) Add hexane, trichloroethylene, dichloromethane or any ratio of two of these solvents to the solution in step (4), centrifuge, and obtain CuInS2 quantum sheets with conjugated molecules passivated.

2. The preparation method according to claim 1, characterized in that, In step (1), the indium source solution is InCl3·4H2O solution, and the molar ratio of the substances is: InCl3·4H2O is 0.15~0.3 mmol, and sulfur powder is 0.15~0.3 mmol; the heating range is 100 ℃~120 ℃ to ensure complete dissolution and no solid impurities remain.

3. The preparation method according to claim 1, characterized in that, In step (2), the copper source solution is a CuI solution, which is prepared by dissolving 0.15 to 0.3 mmol of CuI in 1-3 ml of n-dodecyl mercaptan; injecting the copper source solution when the mixed solution is heated to 160 to 180°C, reacting for 5 to 15 minutes, and then cooling to room temperature.

4. The preparation method according to claim 1, characterized in that, In step (3), the nitrogen-containing heteroatom aromatic compound is selected with a monodentate ligand pyridine molecule; the volume ratio of quantum sheet toluene solution to pyridine solution is 1:3 to 1:6, the reaction temperature is 60℃, the centrifugation rate is 10000 to 12000 r / min, and the centrifugation time is 8 to 15 min; The quantum sheet solution concentration was 20 mg / ml, and the pyridine solution mass fraction was 99.5%.

5. The preparation method according to claim 1, characterized in that, In step (4), the heating temperature of the mixed solution is 60~80 ℃, and the reaction time is 1~2 h.

6. The conjugated molecular passivated cadmium-free two-dimensional quantum sheet prepared by any of the methods in claims 1-5.

7. A method for preparing a CuInS2 quantum sheet-enhanced polymer solar cell, characterized in that, The active layer solution is doped with the conjugated molecular passivation cadmium-free two-dimensional quantum sheet solution described in claim 6.

8. The preparation method according to claim 7, characterized in that, Includes the following steps: (1) A hole transport layer was prepared on a conductive ITO glass substrate by spin coating; (2) The chloroform solution of the pyridine-passivated CuInS2 quantum sheet was mixed with the active layer solution for doping, with a liquid volume doping ratio of 0.5% to 3%; (3) Using spin coating, PM6:Y6:NPLs active layer solution is spin coated onto hole transport layer film; (4) Spin-coating an electron transport layer; (5) A metal electrode is deposited on the surface of the electron transport layer by vacuum deposition.

9. The preparation method according to claim 8, characterized in that, The hole transport layer is made of PEDOT:PSS, PTAA, NiO, or MoO3; the active layer is made of PM6:IT-4F, PM6:Y6, PM6:L8-BO, or PM6:D18; the electron transport layer is made of PDIN, PDINO, NDI-N, or PFN-Br; the electrodes are made of Al, Au, Mn, or Zn; the hole transport layer has a thickness of 50–150 nm; the active layer has a thickness of 150–200 nm; the electron transport layer has a thickness of 30–50 nm; and the electrodes have a thickness of 100–150 nm.

10. CuInS2 quantum sheet polymer solar cells obtained by any of the preparation methods according to claims 7-9.

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