Infrared quantum dot solar cell based on double hole transport layers and preparation method thereof

Abstract

The invention relates to the technical field of PbS quantum dot solar cells, and provides an infrared quantum dot solar cell based on double hole transport layers and a preparation method of the infrared quantum dot solar cell. The infrared quantum dot solar cell comprises a substrate, a bottom electrode, an electron transport layer, a quantum dot photosensitive layer, a hole transport layer and a top electrode which are sequentially stacked, and the hole transport layer comprises a PbS-PbO-EDT hole collection layer and a PbS-PbCl2-EDT hole collection layer which are arranged on the quantum dot photosensitive layer in sequence. The hole transport layer of a double-layer structure is adopted, Cl ligands are introduced, stress caused by volume shrinkage during ligand exchange is reduced, open-circuit voltage and short-circuit current losses caused by cracks on the surface of the film are reduced, meanwhile, the energy band level of the composite film is almost kept unchanged, and voltage losses are avoided.

Description

Technical Field

[0001] This invention relates to the field of PbS quantum dot solar cell technology, and in particular to an infrared quantum dot solar cell based on a double-layer hole transport layer and its preparation method. Background Technology

[0002] Currently, in the field of solar cells, the photoelectric conversion efficiency of silicon-based solar cells and perovskite solar cells, which are most widely used in the market and research, is approaching the Shockley-Queisser efficiency limit. Further breakthroughs in photovoltaic device efficiency are facing increasingly severe challenges. The wavelengths of sunlight reaching the Earth's surface range from 300 to 2500 nm. However, for silicon-based cells, low-energy infrared sunlight with a band gap below the silicon absorber's 1.1 eV cannot be absorbed; that is, light with wavelengths above 1100 nm in the solar spectrum cannot be utilized. This portion of low-energy solar photon energy accounts for approximately 20% of the entire solar spectrum. For perovskite solar cells, the band gap is even wider, resulting in even more unusable infrared light energy. Therefore, collecting this unused low-energy solar photon energy will become an effective way to improve the photoelectric conversion efficiency of traditional photovoltaic devices. Theoretical calculations show that by selecting suitable infrared photovoltaic materials to utilize these dissipated infrared solar photons, an additional absolute power point of approximately 6% can be achieved.

[0003] Among numerous infrared photosensitive materials, PbS and PbSe colloidal quantum dots possess tunable band gaps in the infrared region, effectively collecting infrared light that silicon-based and perovskite solar cells cannot utilize. They also exhibit advantages such as efficient exciton generation, strong quantum confinement effects, ease of solution processing, and good air stability, making them ideal infrared photovoltaic materials. For PbS quantum dots, band gap contraction is typically accompanied by an increase in quantum dot diameter, leading to an increased proportion of the {100} crystal plane—this plane is sensitive to air exposure and extremely difficult to passivate. Therefore, current research on PbS quantum dot infrared solar cells mainly focuses on surface engineering of the photoactive layer quantum dots to improve device performance by suppressing trapped states. However, in PIN structure devices, the hole transport layer is equally crucial in determining the efficiency of PbS quantum dot photovoltaic devices. Inspired by wide-bandgap PbS quantum dot solar cells (~1.38 eV), small-sized PbS quantum dot (~1.4 eV) films treated with 1,2-ethylenedithiol (EDT) are currently used as hole transport layers in narrow-bandgap PbS quantum dot (~0.98 eV) infrared photovoltaic devices, deposited on the photoactive layer via a solid-state ligand exchange process. However, during the ligand exchange process from OA to EDT, the inevitable significant volume shrinkage of the hole transport layer leads to cracks or disordered quantum dot arrangement, while also increasing harmful trapped states and inducing nonradiative recombination of photogenerated carriers, resulting in losses in short-circuit current and open-circuit voltage. Therefore, it is necessary to control the characteristics of the PbS quantum dot hole transport layer, cure the cracks on the surface of the hole transport layer in quantum dot cells, and improve performance. Summary of the Invention

[0004] In view of this, the present invention proposes a novel PbS quantum dot bilayer hole transport structure, which aims to enhance the interfacial carrier extraction capability and thus improve the performance of narrow bandgap PbS quantum dot infrared solar cells.

[0005] The technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides an infrared quantum dot solar cell based on a double-layer hole transport layer, comprising: a substrate, a bottom electrode, an electron transport layer, a quantum dot photosensitive layer, a hole transport layer and a top electrode stacked sequentially; The hole transport layer consists of a PbS-PbO-EDT hole collection layer and a PbS-PbCl2-EDT hole collection layer sequentially disposed on the quantum dot photosensitive layer.

[0006] Specifically, current methods using PbS-EDT as the hole transport layer in battery devices require a solid-state ligand exchange process. However, during the ligand exchange from OA to EDT, the unavoidable significant volume shrinkage of the hole transport layer leads to cracks or disordered quantum dot arrangement, while also increasing harmful trapped states and inducing nonradiative recombination of photogenerated carriers. This invention employs a bilayer hole transport layer and introduces Cl ligands to reduce the stress caused by volume shrinkage during ligand exchange, thereby reducing open-circuit voltage and short-circuit current losses due to cracks on the film surface. Simultaneously, the band structure of the composite film remains almost unchanged, without any voltage loss.

[0007] Based on the above technical solutions, preferably, the thickness of the hole transport layer is 50~80 nm.

[0008] Based on the above technical solutions, preferably, the thickness of the PbS-PbO-EDT hole collection layer and the PbS-PbCl2-EDT hole collection layer is the same.

[0009] Based on the above technical solutions, preferably, the material of the quantum dot photosensitive layer is a PbS halogen ligand quantum dot solution, and the thickness of the quantum dot photosensitive layer is 200~400 nm.

[0010] Specifically, if the photosensitive layer of a quantum dot is too thick, it will affect the separation and extraction of photogenerated carriers, degrading the device efficiency; if the photosensitive layer is too thin, it will not be able to fully absorb infrared photons.

[0011] Based on the above technical solutions, preferably, the material of the electron transport layer is nano-ZnO, and the thickness of the electron transport layer is 35~80 nm.

[0012] Specifically, if the electron transport layer is too thick, it will affect the transport of charge carriers and the transmission of sunlight, while if the electron transport layer is too thin, pinholes may appear, causing the photosensitive layer to come into direct contact with the bottom electrode, both of which will degrade the device performance.

[0013] Based on the above technical solutions, preferably, the substrate is ITO, which also serves as the bottom electrode, and the top electrode is an Au electrode.

[0014] Secondly, the present invention provides a method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer, comprising the following steps: The ITO bottom electrode is cleaned to obtain a clean ITO bottom electrode; Nano-ZnO was spin-coated onto the surface of the ITO bottom electrode to obtain an electron transport layer. A PbS halogen ligand quantum dot solution was spin-coated onto the surface of the electron transport layer to obtain a quantum dot photosensitive layer. A PbS quantum dot solution coated with oleic acid ligands was spin-coated onto the surface of the quantum dot photosensitive layer. The film was then immersed in EDT acetonitrile solution and subsequently cleaned with acetonitrile to obtain a PbS-PbO-EDT hole collecting layer. Then, a PbS-PbCl2 quantum dot solution was spin-coated, and the immersion in EDT acetonitrile solution and the acetonitrile cleaning steps were repeated to obtain a PbS-PbCl2-EDT hole collecting layer. An Au electrode is deposited on the surface of the PbS-PbCl2-EDT hole collection layer to obtain an infrared quantum dot solar cell.

[0015] Based on the above technical solutions, preferably, the first exciton absorption peaks of the PbS quantum dots and PbS-PbCl2 quantum dots coated with oleic acid ligands used in the hole transport layer are located at 880-1000 nm, and the PbS quantum dots coated with oleic acid ligands are prepared by the PbO hot injection method. The PbS-PbCl2 quantum dot solution was prepared using the PbCl2 cation exchange method. The preparation method is as follows: S1, after mixing sulfur source, zinc source, OLA and ODE, react to obtain the first reaction product ZnS quantum dot solution; After S2, PbCl2 and OLA react, ZnS quantum dots, the product of the first reaction, are added, and the reaction continues to obtain a PbS-PbCl2 quantum dot solution.

[0016] In step S1, the sulfur source is thioacetamide, the zinc source is zinc stearate, and the mass-volume ratio of thioacetamide, zinc stearate, OLA and ODE is 0.8-1g:17-18g:65-75mL:20-30mL. In step S2, the mass-volume ratio of PbCl2 and OLA is 1.946-2.919g:27.5-35mL.

[0017] Based on the above technical solutions, preferably, the first exciton absorption peak of the PbS halogen ligand quantum dots in the photosensitive layer is located at 1100~1380 nm, which can effectively achieve the absorption of infrared photons in sunlight. The preparation method of the PbS halogen ligand quantum dot solution is as follows: PbI2 and PbBr2 were dissolved in DMF to obtain a mixed solution, which was then mixed with the PbS-PbCl2 quantum dot solution prepared in step S2 to perform ligand exchange and obtain a PbS halogen ligand quantum dot solution.

[0018] Specifically, liquid-phase ligand exchange is less affected by the environment, has high repeatability, and can achieve full passivation of the quantum dot surface, thereby obtaining quantum dots with good surface defect passivation, and thus obtaining high carrier transport characteristics and low defect density photosensitive layers.

[0019] Based on the above technical solutions, preferably, in the mixed solution, the concentration of PbI2 is 0.1~0.4 mol / L, the concentration of PbBr2 is 0.01~0.05 mol / L, and the volume ratio of the mixed solution to the PbS-PbCl2 quantum dot solution is 1-2:1.

[0020] The infrared quantum dot solar cell based on a double-layer hole transport layer and its fabrication method of the present invention have the following advantages over the prior art: This invention employs a bilayer hole transport layer and introduces Cl ligands to reduce the stress caused by volume shrinkage during ligand exchange, thereby minimizing open-circuit voltage and short-circuit current losses due to surface cracks. Furthermore, the band structure of the composite film remains almost unchanged, without any voltage loss. In addition, this bilayer hole transport layer effectively suppresses trapped states and significantly reduces nonradiative recombination; simultaneously, the energy level matching between it and the narrow-bandgap PbS quantum dot photoactive layer remains almost constant, ensuring the device's charge transport efficiency. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of the infrared quantum dot solar cell based on the double-layer hole transport layer of the present invention; Figure 2 This is a scanning electron microscope image of the surface of the double-layer hole transport layer in Embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the hole transport layer surface in Comparative Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of the hole transport layer surface in Comparative Example 2 of the present invention; Figure 5 This is a scanning electron microscope image of the hole transport layer surface in Comparative Example 3 of the present invention; Figure 6 This is the ultraviolet photoelectron spectrum of the monolayer PbS-PbO-EDT in Embodiment 1 of the present invention; Figure 7 This is the ultraviolet photoelectron spectrum of the double-layer PbS-PbO / PbCl2-EDT in Example 1 of this invention; Figure 8 These are the device band diagrams of Embodiment 1 and Comparative Examples 1-3 of the present invention; Figure 9This is the photoluminescence spectrum of the hole transport layer thin film in an embodiment of the present invention; Figure 10 This is a schematic diagram of the infrared solar cell performance test in an embodiment of the present invention; Figure 11 This is a JV curve diagram of the devices of Embodiment 1 and Comparative Examples 1-3 after 1100 nm filtration.

[0023] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures.

[0024] Figure labeling: 1-Substrate; 2-ITO negative electrode; 3-Gradient ZnO electron transport layer; 4-PbS quantum dot photosensitive layer; 5-PbS-PbO-EDT hole collection layer; 6-PbS-PbCl2-EDT hole collection layer; 7-Au positive electrode. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] On the one hand, this invention provides an infrared quantum dot solar cell based on a double-layer hole transport layer, such as... Figure 1 As shown, the infrared quantum dot solar cell mainly consists of a substrate 1, an ITO negative electrode 2, a gradient ZnO electron transport layer 3, a PbS quantum dot (PbS halogen ligand quantum dot) photosensitive layer 4, a PbS-PbO-EDT hole collection layer 5, a PbS-PbCl2-EDT hole collection layer 6, and an Au positive electrode 7.

[0027] In this structure, an ITO anode 2 is deposited on the surface of substrate 1. The transparency of the substrate and the ITO electrode ensures the transmission of sunlight, and the ITO electrode serves as the bottom electrode (anode). A gradient ZnO electron transport layer 3, serving as an electron collection layer, is spin-coated onto the surface of the ITO anode 2. A PbS quantum dot photosensitive layer 4 is located on the surface of the gradient ZnO electron transport layer 3, serving as the photosensitive layer for the infrared solar cell. A double PbS-EDT quantum dot layer (PbS-PbO-EDT hole collection layer 5 and PbS-PbCl2-EDT hole collection layer 6) is spin-coated onto the surface of the PbS quantum dot photosensitive layer 4, serving as the hole collection layer for the solar cell. This adjusts the band structure and surface film quality of the device, thereby enhancing the carrier transport capability. An Au electrode 6 is evaporated onto the double PbS-EDT quantum dot layer as the top electrode (anode).

[0028] On the other hand, the present invention provides an infrared quantum dot solar cell based on a double-layer hole transport layer, as illustrated by the following embodiments.

[0029] Example 1

[0030] This embodiment provides a method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer, including the following steps: 1. ITO electrode processing method The substrate with ITO electrodes (purchased from Zhuhai Kaiwei Optoelectronics Technology Co., Ltd.) was ultrasonically cleaned and then placed in deionized water, ethanol and acetone for 15 minutes in sequence, and then dried with nitrogen.

[0031] 2. An electron transport layer was prepared using a sol-gel method combined with thermal annealing, including the following steps: 2.1 A zinc source (zinc acetate, dihydrate, 1.5 g) was dissolved in 20 ml of ethylene glycol methyl ether solution, and an appropriate amount (450 µL) of ethanolamine was added as a stabilizer. A homogeneous solution was obtained by stirring. Subsequently, the mixed solution was heated to 60 °C and kept at that temperature for 14 h to obtain the first reaction product, ZnO precursor solution.

[0032] 2.2 The first reaction product was deposited on an ITO / substrate using a spin-coating method at a spin speed of 4000 rpm. Subsequently, the ZnO / ITO / substrate was annealed at 100 °C for 7 min and then annealed at 340 °C for 16 min to promote ZnO crystallization. This process was repeated to obtain a gradient ZnO electron transport layer with a thickness of approximately 52 nm.

[0033] 3. PbS colloidal quantum dots were spin-coated onto a gradient ZnO electron transport layer in an N2 glove box to obtain a quantum dot photosensitive layer. The preparation method includes three processes: quantum dot synthesis, liquid-phase ligand exchange, and thin film deposition.

[0034] 3.1 The synthesis process of PbS colloidal quantum dots is as follows: Synthesis of ZnS quantum dots: 0.9 g of thioacetamide and 17.64 g of zinc stearate were added to 70 mL of ODE (octadecene) and 24 mL of OLA (oleylamine), and degassed for 15 min. Then, the mixture was heated to 140 °C in N2 environment and held for 50 min. After the reaction was completed, the mixture was cooled to 40 °C in a water bath and 8 mL of n-octylamine was injected. The reaction was stopped after the solution turned colorless. The quantum dots were washed with n-hexane and ethanol to obtain ZnS quantum dots dispersed in the ODE solution (ZnS ODE solution).

[0035] PbS quantum dot growth: 1.946 g PbCl2 was dissolved in 27.5 mL OLA (oleylamine) and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 1.8 mL of the above ZnSODE solution was rapidly injected. After the reaction was completed, the above ZnS ODE solution was added dropwise over a period of 2 h, resulting in PbS quantum dots with exciton absorption peaks at ~1250 nm.

[0036] 3.2 The process of liquid-phase ligand exchange is as follows: A certain amount of PbI2 and PbBr2 were dissolved in DMF solution to prepare a mixed solution with a concentration of 0.3 mol / L PbI2 and 0.04 mol / L PbBr2.

[0037] Add 10 mL of PbS quantum dot solution (8 mg / mL) dispersed in n-octane to 10 mL of the above mixed solution and shake vigorously to achieve ligand exchange.

[0038] The exchanged halogen-coated PbS quantum dots were washed with n-octane, centrifuged, and dried under vacuum for 30 min to obtain the dried product.

[0039] 3.3 The thin film deposition process is as follows: The dried product was dispersed in a BTA / DMF (volume ratio 7:3) mixed solution to prepare a quantum dot solution with a concentration of 320 mg / mL.

[0040] A PbS quantum dot photosensitive layer was prepared by spin-coating a quantum dot solution onto a gradient ZnO layer. The spin-coating process was 2500 rpm / 50s, resulting in a PbS QDs / gradient ZnO / ITO thin film.

[0041] The PbS QDs / gradient ZnO / ITO film was baked at 90 °C for 10 min to evaporate the residual solvent, resulting in a quantum dot photosensitive layer with a thickness of 240 nm.

[0042] 4. A bilayer PbS-EDT quantum dot hole transport layer was prepared by spin-coating onto a quantum dot photosensitive layer. Two types of PbS quantum dots were used, both with the first exciton absorption peak located at ~880 nm. The specific synthesis methods for the two types are as follows: 4.1 PbO hot injection method: 0.9 g PbO was dissolved in a mixed solution of 20 mL ODE (octadecene) and 3 mL OLA (oleylamine), then heated to 80 °C in a nitrogen atmosphere and evacuated for 6 h. Then, 10 mL ODE and 420 µL TMS (bis(trimethylsilyl) sulfide) were rapidly injected, and the reaction was carried out for 2 min. The solution was washed with ethyl acetate, ethanol and n-hexane to obtain a PbS-PbO quantum dot solution with the first exciton absorption peak located at ~880 nm.

[0043] 4.2 PbCl2 cation exchange method: 2.919 g of PbCl2 was dissolved in 35 mL of OLA and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 5 mL of the above ZnSODE solution (prepared in step 3.1) was quickly injected. After the reaction was completed for 15 s, the above ZnS ODE solution (prepared in step 3.1) was added dropwise over a period of 40 min to obtain a PbS-PbCl2 quantum dot solution with an exciton absorption peak at ~880 nm.

[0044] The method for preparing a bilayer PbS-EDT quantum dot hole transport layer includes the following steps: 1) Spin-coat the PbS-PbO quantum dot solution onto the quantum dot photosensitive layer in step S3 at a spin-coating speed of 2500 rpm.

[0045] 2) Add EDT (1,2-ethylenedithiol) acetonitrile solution (EDT diluted with acetonitrile to a volume concentration of 0.01%) to the PbS quantum dot film described in step 1, soak for 15 seconds, and then wash the residual EDT with acetonitrile to obtain a PbS-PbO-EDT hole collection layer with a thickness of 30 nm.

[0046] 3) The PbS-PbCl2 quantum dot solution prepared in step S42 was spin-coated onto the surface of the PbS-PbO-EDT hole collection layer at a spin-coating speed of 2500 rpm.

[0047] 4) Repeat step 2 to obtain a PbS-PbCl2-EDT hole collection layer with a thickness of 30nm.

[0048] 5. A hole collection layer with an area of ​​0.09 cm² was deposited on the PbS-PbCl2-EDT using a vapor deposition method. 2 Au electrodes were used to complete the fabrication of a PbS quantum dot infrared solar cell with a double hole transport layer.

[0049] Example 2

[0050] This embodiment provides a method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer, including the following steps: The deposition method for the ITO electrode is the same as in Example 1.

[0051] 2. An electron transport layer was prepared using a sol-gel method combined with thermal annealing, including the following steps: 2.1 Same as Example 1.

[0052] 2.2 The first reaction product was deposited on an ITO / substrate using a spin-coating method at a spin speed of 4000 rpm. Subsequently, the ZnO / ITO / substrate was annealed at 100 °C for 7 min and then annealed at 340 °C for 16 min to promote ZnO crystallization. This process was repeated to obtain a gradient ZnO electron transport layer with a thickness of approximately 35 nm.

[0053] 3. PbS colloidal quantum dots were spin-coated onto a gradient ZnO electron transport layer in an N2 glove box to obtain a quantum dot photosensitive layer. The preparation method includes three processes: quantum dot synthesis, liquid-phase ligand exchange, and thin film deposition.

[0054] 3.1 The synthesis process of PbS colloidal quantum dots is as follows: Synthesis of ZnS quantum dots: 0.9 g of thioacetamide and 17.64 g of zinc stearate were added to 70 mL of ODE (octadecene) and 24 mL of OLA (oleylamine), and degassed for 15 min. Then, the mixture was heated to 140 °C in N2 environment and held for 50 min. After the reaction was completed, the mixture was cooled to 40 °C in a water bath and 8 mL of n-octylamine was injected. The reaction was stopped after the solution turned colorless. The quantum dots were washed with n-hexane and ethanol to obtain ZnS quantum dots dispersed in the ODE solution (ZnS ODE solution).

[0055] PbS quantum dot growth: 1.946 g PbCl2 was dissolved in 27.5 mL OLA (oleylamine) and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 1.8 mL of the above ZnSODE solution was rapidly injected. After the reaction was completed, the above ZnS ODE solution was added dropwise over a period of 2 h, resulting in PbS quantum dots with exciton absorption peaks at ~1250 nm.

[0056] 3.2 The process of liquid-phase ligand exchange is as follows: A certain amount of PbI2 and PbBr2 were dissolved in DMF solution to prepare a mixed solution with a concentration of 0.1 mol / L PbI2 and 0.01 mol / L PbBr2.

[0057] Add 10 mL of PbS quantum dot solution (8 mg / mL) dispersed in n-octane to 10 mL of the above mixed solution and shake vigorously to achieve ligand exchange.

[0058] The exchanged halogen-coated PbS quantum dots were washed with n-octane, centrifuged, and dried under vacuum for 30 min to obtain the dried product.

[0059] 3.3 The thin film deposition process is as follows: The dried product was dispersed in a BTA / DMF (volume ratio 7:3) mixed solution to prepare a quantum dot solution with a concentration of 320 mg / mL.

[0060] A PbS quantum dot photosensitive layer was prepared by spin-coating a quantum dot solution onto a gradient ZnO layer. The spin-coating process was 2500 rpm / 50s, resulting in a PbS QDs / gradient ZnO / ITO thin film.

[0061] The PbS QDs / gradient ZnO / ITO film was baked at 90 °C for 10 min to evaporate the residual solvent, resulting in a quantum dot photosensitive layer with a thickness of 200 nm.

[0062] 4. A bilayer PbS-EDT quantum dot hole transport layer was prepared by spin-coating onto a quantum dot photosensitive layer. Two types of PbS quantum dots were used, both with the first exciton absorption peak located at ~880 nm. The specific synthesis methods for the two types are as follows: 4.1 The PbO hot injection method is the same as in Example 1.

[0063] 4.2 PbCl2 cation exchange method: 2.919 g of PbCl2 was dissolved in 35 mL of OLA and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 5 mL of the above ZnSODE solution (prepared in step 3.1) was quickly injected. After the reaction was completed for 15 s, the above ZnS ODE solution (prepared in step 3.1) was added dropwise over a period of 40 min to obtain a PbS-PbCl2 quantum dot solution with an exciton absorption peak at ~880 nm.

[0064] The method for preparing a bilayer PbS-EDT quantum dot hole transport layer includes the following steps: 1) Spin-coat the PbS-PbO quantum dot solution onto the quantum dot photosensitive layer in step S3 at a spin-coating speed of 2500 rpm.

[0065] 2) Add EDT (1,2-ethylenedithiol) acetonitrile solution (EDT diluted with acetonitrile to a volume concentration of 0.01%) to the PbS quantum dot film described in step 1, soak for 15 seconds, and then wash the residual EDT with acetonitrile to obtain a PbS-PbO-EDT hole collection layer with a thickness of 25 nm.

[0066] 3) The PbS-PbCl2 quantum dot solution prepared in step S42 was spin-coated onto the surface of the PbS-PbO-EDT hole collection layer at a spin-coating speed of 2500 rpm.

[0067] 4) Repeat step 2 to obtain a PbS-PbCl2-EDT hole collection layer with a thickness of 25nm.

[0068] 5. A hole collection layer with an area of ​​0.09 cm² was deposited on the surface of the PbS-PbCl2-EDT using a vapor deposition method. 2 Au electrodes were used to complete the fabrication of a PbS quantum dot infrared solar cell with a double-layer hole transport layer.

[0069] Example 3

[0070] This embodiment provides a method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer, including the following steps: The deposition method for the ITO electrode is the same as in Example 1.

[0071] 2. An electron transport layer was prepared using a sol-gel method combined with thermal annealing, including the following steps: 2.1 Same as Example 1.

[0072] 2.2 The first reaction product was deposited on an ITO / substrate using a spin-coating method at a spin speed of 4000 rpm. Subsequently, the ZnO / ITO / substrate was annealed at 100 °C for 7 min and then annealed at 340 °C for 16 min to promote ZnO crystallization. This process was repeated to obtain a gradient ZnO electron transport layer with a thickness of approximately 80 nm.

[0073] 3. PbS colloidal quantum dots were spin-coated onto a gradient ZnO electron transport layer in an N2 glove box to obtain a quantum dot photosensitive layer. The preparation method includes three processes: quantum dot synthesis, liquid-phase ligand exchange, and thin film deposition.

[0074] 3.1 The synthesis process of PbS colloidal quantum dots is as follows: Synthesis of ZnS quantum dots: 0.9 g of thioacetamide and 17.64 g of zinc stearate were added to 70 mL of ODE (octadecene) and 24 mL of OLA (oleylamine), and degassed for 15 min. Then, the mixture was heated to 140 °C in N2 environment and held for 50 min. After the reaction was completed, the mixture was cooled to 40 °C in a water bath and 8 mL of n-octylamine was injected. The reaction was stopped after the solution turned colorless. The quantum dots were washed with n-hexane and ethanol to obtain ZnS quantum dots dispersed in the ODE solution (ZnS ODE solution).

[0075] PbS quantum dot growth: 1.946 g PbCl2 was dissolved in 27.5 mL OLA (oleylamine) and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 1.8 mL of the above ZnSODE solution was rapidly injected. After the reaction was completed, the above ZnS ODE solution was added dropwise over a period of 2 h, resulting in PbS quantum dots with exciton absorption peaks at ~1250 nm.

[0076] 3.2 The process of liquid-phase ligand exchange is as follows: A certain amount of PbI2 and PbBr2 were dissolved in DMF solution to prepare a mixed solution with a concentration of 0.4 mol / L PbI2 and 0.05 mol / L PbBr2.

[0077] Add 10 mL of PbS quantum dot solution (8 mg / mL) dispersed in n-octane to 10 mL of the above mixed solution and shake vigorously to achieve ligand exchange.

[0078] The exchanged halogen-coated PbS quantum dots were washed with n-octane, centrifuged, and dried under vacuum for 30 min to obtain the dried product.

[0079] 3.3 The thin film deposition process is as follows: The dried product was dispersed in a BTA / DMF (volume ratio 7:3) mixed solution to prepare a quantum dot solution with a concentration of 320 mg / mL.

[0080] A PbS quantum dot photosensitive layer was prepared by spin-coating a quantum dot solution onto a gradient ZnO layer. The spin-coating process was 2500 rpm / 50s, resulting in a PbS QDs / gradient ZnO / ITO thin film.

[0081] The PbS QDs / gradient ZnO / ITO film was baked at 90 °C for 10 min to evaporate the residual solvent, resulting in a quantum dot photosensitive layer with a thickness of 400 nm.

[0082] 4. A bilayer PbS-EDT quantum dot hole transport layer was prepared by spin-coating onto the photosensitive layer. Two types of PbS quantum dots were used, both with the first exciton absorption peak located at ~880 nm. The specific synthesis methods for the two types are as follows: 4.1 The PbO hot injection method is the same as in Example 1.

[0083] 4.2 PbCl2 cation exchange method: 2.919 g of PbCl2 was dissolved in 35 mL of OLA and degassed for 15 min. Then, it was heated to 140 °C in N2 environment and held for 30 min. After heating was stopped and cooled to 60 °C, 5 mL of the above ZnSODE solution (prepared in step 3.1) was quickly injected. After the reaction was completed for 15 s, the above ZnS ODE solution (prepared in step 3.1) was added dropwise over a period of 40 min to obtain a PbS (PbCl2) quantum dot solution with exciton absorption peaks at ~880 nm.

[0084] The method for preparing a bilayer PbS-EDT quantum dot hole transport layer includes the following steps: 1) Spin-coat the PbS-PbO quantum dot solution onto the quantum dot photosensitive layer in step S3 at a spin-coating speed of 2500 rpm.

[0085] 2) Add EDT (1,2-ethylenedithiol) acetonitrile solution (EDT diluted with acetonitrile to a volume concentration of 0.01%) to the PbS quantum dot film described in step 1, soak for 15 seconds, and then wash the residual EDT with acetonitrile to obtain a PbS-PbO-EDT hole collection layer with a thickness of 40 nm.

[0086] 3) The PbS-PbCl2 quantum dot solution prepared in step S42 was spin-coated onto the surface of the PbS-PbO-EDT hole collection layer at a spin-coating speed of 2500 rpm.

[0087] 4) Repeat step 2 to obtain a PbS-PbCl2-EDT hole collection layer with a thickness of 40nm.

[0088] 5. A hole collection layer with an area of ​​0.09 cm² was deposited on the PbS-PbCl2-EDT using a vapor deposition method. 2 Au electrodes were used to complete the fabrication of a PbS quantum dot infrared solar cell with a double-layer hole transport layer.

[0089] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that in the preparation method of the hole transport layer in step S4, both spin coatings are PbS-PbCl2 quantum dot solutions, and the rest is the same as in Example 1.

[0090] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that in the preparation method of the hole transport layer in step S4, both spin coatings are PbS-PbO quantum dot solutions, and the rest is the same as in Example 1.

[0091] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that in the preparation method of the hole transport layer in step S4, PbS-PbCl2 quantum dot solution is first spin-coated, and then PbS-PbO quantum dot solution is spin-coated. The rest of the contents are the same as in Example 1.

[0092] Figure 2 The image shows a surface scanning electron microscope image of the hole transport layer in Example 1, where a PbS-PbCl2-EDT layer is introduced at the top layer to fill the film cracks.

[0093] Figure 3 The image shows a surface scanning electron microscope image of the hole transport layer in Comparative Example 1, where the film cracks are filled due to the presence of the PbS-PbCl2-EDT layer.

[0094] Figure 4 The image shown is a scanning electron microscope image of the surface of the double-layer hole transport layer in Comparative Example 2. Cracks caused by compressive stress can be seen on the surface of the thin film.

[0095] Figure 5 The image shown is a scanning electron microscope image of the surface of the double-layer hole transport layer in Comparative Example 3. Cracks caused by compressive stress can be seen on the surface of the uppermost thin film PbS-PbO-EDT.

[0096] Figure 6 The ultraviolet photoelectron spectrum of PbS-PbO-EDT in Example 1; Figure 7 The ultraviolet photoelectron spectrum of the bilayer PbS-PbO / PbCl2-EDT in Example 1 shows that the band structure of the bilayer PbS-PbO / PbCl2 is almost identical to that of the monolayer PbS-PbO-EDT.

[0097] Figure 8 The band diagrams for Example 1 and Comparative Examples 1-3 show that the band levels of bilayer PbS-PbO / PbCl2 are almost identical to those of monolayer PbS-PbO-EDT. The band matching between monolayer PbS-PbCl2 and bilayer PbS-PbCl2 / PbO and the photosensitive layer is poor.

[0098] Figure 9 The photoluminescence spectra of PbS-PbO and PbS-PbCl2 in Example 1 of this invention confirm that defects in the gradient electron transport layer are suppressed.

[0099] Figure 10 This is a schematic diagram of the performance test of the PbS quantum dot infrared photovoltaic device prepared in this invention. The experimental performance was tested after the experimental device was filtered at 1100nm.

[0100] Figure 11The infrared JV curves of the devices after filtering with an 1100 nm filter in Embodiment 1 and Comparative Examples 1-3 of the present invention can be seen. It can be seen that the infrared open-circuit voltage, short-circuit current and other performance of the device in Embodiment 1 are significantly improved.

[0101] The performance of the infrared quantum dot solar cells prepared in Example 1 and Comparative Examples 1-3 was tested: I. JV Feature Testing Under simulated AM 1.5G sunlight conditions (100 mW / cm², generated by a 450 W xenon lamp (Newport)), the current density-voltage (JV) characteristic curves of Examples 1-4 were measured using a Keithley 2400 source meter. For infrared filtering tests, an 1100 nm long-pass dielectric filter (Thorlabs FELH1100) was placed in front of the light source to acquire the JV curves of the device under infrared illumination; the results are shown in Tables 1-2. The electrode area is 0.09 cm². 2 The voltage test interval is 5mV.

[0102] Table 1. JV characteristic parameters of infrared quantum dot solar cells after 1100nm filtering.

[0103] As can be seen from Table 1, Example 1, which uses the double-layer hole transport layer of the present invention, has better infrared short-circuit current, open-circuit voltage, fill factor and photoelectric conversion efficiency than Comparative Examples 1-3.

[0104] Table 2 JV characteristic parameters of quantum dot solar cells under AM1.5 illumination

[0105] As can be seen from Table 2, Example 4, which uses the double-layer hole transport layer of the present invention, has better short-circuit current, open-circuit voltage, fill factor and photoelectric conversion efficiency under AM1.5 illumination than Examples 1-3, just like under infrared filtering.

[0106] II. Repeatability Testing Ten solar cell devices were prepared according to the methods of Example 1 and Comparative Examples 1-3, and tested using the methods described above. The results are shown in Table 3.

[0107] Table 3. Average JV characteristic parameters and variance of 10 solar cells

[0108] As can be seen from Table 3, the average photoelectric conversion efficiency of the solar cell device of Example 1 using the double hole transport layer of the present invention is better than that of Comparative Examples 1-3 under AM1.5 and 1100nm filtering conditions, indicating that Example 1 has high photoelectric conversion efficiency and good repeatability.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An infrared quantum dot solar cell based on a double-layer hole transport layer, characterized in that, include: A substrate, a bottom electrode, an electron transport layer, a quantum dot photosensitive layer, a hole transport layer, and a top electrode are stacked sequentially. The hole transport layer consists of a PbS-PbO-EDT hole collection layer and a PbS-PbCl2-EDT hole collection layer sequentially disposed on the quantum dot photosensitive layer.

2. An infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 1, characterized in that, The thickness of the hole transport layer is 50~80 nm.

3. An infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 1, characterized in that, The substrate is glass, the bottom electrode is an ITO electrode, and the top electrode is an Au electrode; The quantum dot photosensitive layer is made of a PbS halogen ligand quantum dot solution with a thickness of 200~400 nm. The electron transport layer is made of nano-ZnO with a thickness of 35~80 nm.

4. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 3, characterized in that, Includes the following steps: A PbS quantum dot solution coated with oleic acid ligands was spin-coated onto the surface of the quantum dot photosensitive layer. The film was then immersed in EDT acetonitrile solution and subsequently cleaned with acetonitrile to obtain a PbS-PbO-EDT hole collecting layer. Then, a PbS-PbCl2 quantum dot solution was spin-coated, and the immersion in EDT acetonitrile solution and the acetonitrile cleaning steps were repeated to obtain a PbS-PbCl2-EDT hole collecting layer.

5. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 4, characterized in that, The first exciton absorption peaks of the oleic acid ligand-coated PbS quantum dots and the PbS-PbCl2 quantum dots are both located in the range of 880–1000 nm.

6. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 4, characterized in that, The preparation method of the PbS-PbCl2 quantum dot solution is as follows: S1, after mixing sulfur source, zinc source, OLA and ODE, react to obtain the first reaction product ZnS quantum dot solution; After S2, PbCl2 and OLA react, ZnS quantum dots, the product of the first reaction, are added, and the reaction continues to obtain a PbS-PbCl2 quantum dot solution.

7. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 6, characterized in that, In step S1, the sulfur source is thioacetamide, the zinc source is zinc stearate, and the mass-volume ratio of thioacetamide, zinc stearate, OLA and ODE is 0.8-1g:17-18g:65-75mL:20-30mL. In step S2, the mass-volume ratio of PbCl2 and OLA is 1.946-2.919g:27.5-35mL.

8. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 6, characterized in that, The preparation method of the PbS halogen ligand quantum dot solution is as follows: PbI2 and PbBr2 were dissolved in DMF to obtain a mixed solution, which was then mixed with the PbS-PbCl2 quantum dot solution prepared in step S2 to perform ligand exchange and obtain a PbS halogen ligand quantum dot solution.

9. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 8, characterized in that, In the mixed solution, the concentration of PbI2 is 0.1~0.4 mol / L, the concentration of PbBr2 is 0.01~0.05 mol / L, and the volume ratio of the mixed solution to the PbS-PbCl2 quantum dot solution is 1-2:

1.

10. The method for fabricating an infrared quantum dot solar cell based on a double-layer hole transport layer as described in claim 8, characterized in that, The first exciton absorption peak of the PbS halogen ligand quantum dots in the photosensitive layer is located at 1100~1380 nm.

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