Flexible narrow-bandgap perovskite solar cells doped with scecs and methods of making the same

Abstract

This application relates to the field of solar cell technology, specifically to a flexible narrow-bandgap perovskite solar cell doped with SCEC and its fabrication method. It comprises, from bottom to top, a flexible transparent conductive substrate, a hole transport layer, a narrow-bandgap perovskite absorber layer, an electron transport layer, a hole blocking layer, and a metal electrode layer, stacked sequentially. The hole transport layer is made of SCEC-doped PEDOT:PSS. By introducing SCEC into the hole transport layer, the conductivity and chemical properties of PEDOT:PSS can be improved through multi-site coordination and synergistic effects of functional groups. This effectively regulates the wettability and polarity of the hole transport layer surface, promoting uniform nucleation and controllable crystallization of the perovskite precursor solution at the front interface, thereby facilitating the formation of a more uniform and dense perovskite thin film on the flexible substrate.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a flexible narrow-bandgap perovskite solar cell doped with SCEC (S-(2-carboxyethyl)-L-cysteine) and its preparation method. Background Technology

[0002] Perovskite materials possess excellent photoelectric properties, giving them a significant advantage in emerging photovoltaic fields. The power conversion efficiency (PCE) of rigid-substrate double-ended all-perovskite tandem solar cells has exceeded 30.1%, highlighting the potential of all-perovskite tandem systems in high-efficiency photovoltaic devices. Simultaneously, the mechanical flexibility and low-temperature solution preparation advantages of perovskite materials enable the fabrication of flexible photovoltaic devices. Flexible perovskite devices are lightweight, bendable, and wearable, making them suitable for portable power supply and curved surface integration applications. In recent years, the photovoltaic performance and mechanical flexibility of flexible perovskite solar cells have improved significantly, with the PCE of flexible all-perovskite tandem solar cells exceeding 27%, showing promising prospects.

[0003] In flexible all-perovskite tandem solar cell systems, the narrow-bandgap Sn-Pb perovskite bottom cell plays a decisive role in near-infrared light absorption, photocurrent output, and overall tandem efficiency. However, flexible narrow-bandgap perovskite solar cells face several challenges: firstly, the Sn content in Sn-Pb narrow-bandgap perovskite... 2+ Easily oxidized to Sn 4+ This leads to problems such as high-density defect states and uneven tin-lead crystallization rates. Secondly, compared to rigid devices, flexible substrates have lower heat resistance, larger differences in the mechanical modulus of the film layers, and interface stress concentration during bending. This poses significant challenges to the efficiency and mechanical stability of flexible narrow bandgap devices.

[0004] The hole transport layer, serving as the interface between the flexible substrate and the perovskite absorber layer, significantly impacts the efficiency and bending durability of flexible narrow bandgap devices. The quality of the front interface determines charge transport and interfacial recombination losses, and front interface issues are more critical in flexible narrow bandgap perovskite devices. Currently, PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) is widely used as the hole transport layer in flexible narrow bandgap perovskite solar cells due to its low-temperature processing capability and good compatibility with flexible substrates. However, PEDOT:PSS suffers from problems such as strong acidity and hygroscopicity, limited interfacial energy level matching, and insufficient control over perovskite film formation. Furthermore, research on functional molecular doping of the PEDOT:PSS hole transport layer in flexible narrow bandgap perovskite solar cells to improve flexible substrate contact, perovskite film formation, and bending stability is still limited, resulting in a lack of effective pathways to improve the performance and stability of flexible devices. Therefore, it is urgent to develop hole transport layer doping strategies suitable for flexible narrow bandgap perovskite solar cells to address these issues. Summary of the Invention

[0005] The purpose of this invention is to provide a flexible narrow bandgap perovskite solar cell. By doping the hole transport layer with SCEC, the conductivity and chemical properties of PEDOT:PSS are controlled, further improving the wetting, spreading and interfacial bonding performance of the front interface, thereby promoting the uniform crystallization of the narrow bandgap perovskite film and achieving a significant improvement in the performance of the flexible narrow bandgap perovskite solar cell.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a flexible narrow-bandgap perovskite solar cell doped with SCEC, comprising a flexible transparent conductive substrate, a hole transport layer, a narrow-bandgap perovskite absorber layer, an electron transport layer, a hole blocking layer, and a metal electrode layer stacked sequentially from bottom to top; The hole transport layer is made of PEDOT:PSS doped with SCEC, and the doping amount of SCEC is 1 mg / mL to 2 mg / mL compared to the PEDOT:PSS aqueous dispersion. The chemical formula of the narrow bandgap perovskite absorber layer is FA. 0.7 MA 0.3 Sn 0.5 Pb 0.5 I3.

[0007] Furthermore, the thickness of the narrow bandgap perovskite absorber layer is any value between 1000 nm and 1200 nm; The thickness of the hole transport layer is any value between 30nm and 50nm.

[0008] Furthermore, the thickness of the flexible transparent conductive substrate is any value between 80μm and 150μm to ensure that the average light transmittance of the flexible transparent conductive substrate is not less than 80% and the sheet resistance is in the range of 10Ω / sq to 20Ω / sq.

[0009] Furthermore, the material of the electron transport layer is C. 60 The thickness is any value between 20nm and 30nm; The hole blocking layer is made of BCP and has a thickness of any value between 6nm and 8nm. The thickness of the metal electrode layer is any value between 100 nm and 200 nm.

[0010] This application also provides a method for fabricating the above-mentioned flexible narrow bandgap perovskite solar cell, including the following steps: S1. Obtain a flexible transparent conductive substrate, coat the flexible transparent conductive substrate with a PEDOT:PSS aqueous dispersion doped with SCEC, and after coating, perform annealing treatment to form a hole transport layer on the flexible transparent conductive substrate. S2. Prepare a perovskite precursor solution, spin-coat the perovskite precursor solution onto the hole transport layer using a two-step spin-coating method, and add antisolvent during the spin-coating process. Then, perform stepwise annealing to form a perovskite film on the hole transport layer. S3. Perform back passivation treatment on the perovskite film to form a narrow bandgap perovskite absorption layer on the hole transport layer; S4. An electron transport layer, a hole blocking layer, and a metal electrode layer are sequentially deposited on the surface of the narrow bandgap perovskite absorber layer to obtain a flexible narrow bandgap perovskite solar cell doped with SCEC.

[0011] Further, in step S1, the solid content of the PEDOT:PSS aqueous dispersion is 1%–3%; and the annealing treatment temperature is 100℃–130℃.

[0012] Further, in step S2, the preparation of the perovskite precursor solution includes: dissolving the raw material group including PbI2, SnI2, MAI and FAI in a DMF / DMSO mixed solvent, stirring at room temperature for a certain period of time, and then filtering using a filter membrane; The concentration of perovskite material in the perovskite precursor solution is any value between 2 mol / L and 2.5 mol / L.

[0013] Further, in step S2, the two-step annealing process includes: high-temperature annealing at a temperature of 80℃~120℃, and then low-temperature annealing at a temperature of 55℃~70℃.

[0014] Further, in step S2, the two-step spin coating method includes: first, performing low-speed spin coating at a rotation speed of 800 rpm to 1200 rpm, and then performing high-speed spin coating at a rotation speed of 3500 rpm to 5000 rpm, and adding anti-solvent dropwise during the high-speed spin coating process, wherein the amount of anti-solvent added is 500 μL to 700 μL, and the drop rate is 300 μL / s to 500 μL / s.

[0015] Further, in step S3, the back passivation treatment includes: spin-coating the back passivation solution onto the perovskite film at a rotation speed of 3000 rpm to 5000 rpm, and immediately transferring it to a temperature of 90℃ to 120℃ for annealing after spin-coating. The back passivation solution is prepared by dissolving ethylenediamine diiodide powder in IPA solution, and the concentration of the back passivation solution is any value between 0.5 mg / mL and 1.5 mg / mL.

[0016] The beneficial effects of this invention are as follows: The flexible narrow bandgap perovskite solar cell provided in this application, by introducing S-(2-carboxyethyl)-L-cysteine ​​into the hole transport layer, can utilize multi-site coordination and functional group synergy to improve the conductivity and chemical properties of PEDOT:PSS, effectively regulate the wettability and polarity of the hole transport layer surface, promote the uniform nucleation and controllable crystallization of the perovskite precursor solution at the front interface, and thus facilitate the formation of a more uniform and dense narrow bandgap Sn-Pb perovskite thin film on the flexible substrate, significantly improving the overall photovoltaic performance of the finally obtained flexible narrow bandgap perovskite solar cell.

[0017] The dicarboxyl group and other functional groups in the S-(2-carboxyethyl)-L-cysteine ​​molecule can provide more interaction sites, which helps to improve the wettability of the hole transport layer surface and the compatibility between the hole transport layer and the flexible substrate. At the same time, it can also enhance the passivation effect on the interface defect sites of perovskite thin films, reduce the interface trap state density, and thus effectively suppress nonradiative recombination, improve carrier extraction and transport efficiency, and achieve the effect of improving the open circuit voltage, fill factor and photoelectric conversion performance of flexible devices.

[0018] The flexible narrow-bandgap perovskite solar cell provided in this application is an inverted structure constructed based on an ITO / PEN flexible transparent conductive substrate. It incorporates a hole transport layer doping strategy to enhance the interfacial bonding performance between functional layers and optimize interface matching, effectively mitigating interface mismatch and performance degradation issues during bending. This is not only suitable for flexible narrow-bandgap single-junction perovskite solar cells but also shows promising application prospects in flexible all-perovskite tandem solar cells.

[0019] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a flexible narrow bandgap perovskite solar cell according to an embodiment of the present invention; Figure 2 SEM images of the perovskite films prepared in Example 1, Comparative Examples 1 and 2 of the present invention. Figure 3 AFM images of the perovskite films prepared in Example 1, Comparative Examples 1 and 2 of this invention; Figure 4 SEM images of the buried interface of the perovskite thin film prepared in Example 1, Comparative Examples 1 and 2 of the present invention; Figure 5The image shows Sn3d X-ray photoelectron spectroscopy (XPS) spectra of the buried interface of the perovskite thin film prepared in Example 1, Comparative Examples 1 and 2 of this invention. Figure 6 The steady-state photoluminescence (PL) spectra of the perovskite thin films prepared in Example 1, Comparative Examples 1 and 2 of this invention are shown. Figure 7 The JV performance statistics of the flexible narrow bandgap perovskite solar cells prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown in the figure. Figure 8 The JV curves are shown for the flexible narrow bandgap perovskite solar cells prepared in Embodiment 1 and Comparative Example 1 of this invention. Figure 9 The EQE spectra of the flexible narrow bandgap perovskite solar cells prepared in Example 1 and Comparative Example 1 of this invention are shown below. Figure 10 Hysteresis test diagrams of the flexible narrow bandgap perovskite solar cells prepared in Embodiment 1 and Comparative Example 1 of the present invention. Figure 11 This is a JV curve diagram of the experimental group and the control group shown in this invention; Figure 12 The EQE spectrum of the flexible two-terminal all-perovskite tandem solar cell shown in this invention is shown. Figure label: 1. Flexible transparent conductive substrate; 2. Hole transport layer; 3. Narrow bandgap perovskite absorber layer; 4. Electron transport and hole blocking layer; 5. Metal electrode layer. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] It should be noted that, unless otherwise specified, all raw materials used in this application are commercially available.

[0024] It should be noted that the performance of the fabricated flexible narrow-bandgap perovskite solar cell was tested in this application using the following method: Power conversion efficiency (PCE): at 100mW cm -2The light intensity was measured under AM 1.5G solar simulator illumination (SS-F5-3A, Enlitech) using a Keithley 2400 source meter, and calibrated against a standard silicon solar cell.

[0025] Open circuit voltage (V) OC ): at 100mW cm -2 Under AM 1.5G solar simulator illumination (SS-F5-3A, Enlitech), using a Keithley 2400 source meter, the measured light intensity was calibrated with a standard silicon solar cell.

[0026] External quantum efficiency (EQE) test: EQE measurements are performed using an EQE system (QE-R, Enlitech) under near-dark test conditions.

[0027] X-ray photoelectron spectroscopy (XPS) analysis was performed on the perovskite thin film using an ESCALAB 250Xi (Thermal Fisher Scientific) spectrometer.

[0028] Photoluminescence (PL) measurements were performed in ambient air at room temperature using a 532 nm continuous-wave laser as the excitation source (beam diameter ≈ 90 μm) with an excitation power density of approximately 40 mW / cm². Incident measurements were conducted from both the perovskite thin film side and the flexible substrate side to characterize the photogenerated carrier recombination behavior at the top surface and buried interface, respectively. A 300 gmm² laser was used. -1 After the grating monochromator (integration time = 0.5s), the PL signal is detected by the Symphony-II CCD (from Horiba) detector.

[0029] Scanning electron microscopy (SEM) tests: The top view of the perovskite thin film was characterized using field emission scanning electron microscopes (Hitachi S-4800 and ZEISS Sigma300).

[0030] Atomic force microscopy (AFM) was used to characterize the top view of the flexible perovskite film in tapping mode, with a scanning range of 5 × 5 μm. 2 The main test is for surface roughness (Ra).

[0031] like Figure 1As shown, the flexible narrow-bandgap perovskite solar cell doped with SCEC prepared in Example 1 of this application includes a flexible transparent conductive substrate 1, a hole transport layer 2, a narrow-bandgap perovskite absorber layer 3, an electron transport and hole blocking layer 4, and a metal electrode layer 5, stacked sequentially from bottom to top. The electron transport and hole blocking layer 4 includes an electron transport layer and a hole blocking layer. The hole transport layer 2 is doped with S-(2-carboxyethyl)-L-cysteine, meaning the material of the hole transport layer 2 is PEDOT:PSS doped with S-(2-carboxyethyl)-L-cysteine, and the doping amount of S-(2-carboxyethyl)-L-cysteine ​​is 1 mg / mL to 2 mg / mL compared to the PEDOT:PSS aqueous dispersion. The perovskite material selected for the narrow-bandgap perovskite absorber layer 3 has the chemical formula FA. 0.7 MA 0.3 Sn 0.5 Pb 0.5 I3, and this perovskite material has an ABX3 structure. Specifically, FA (formamidinium) and MA (methylamine) are at the A site, with FA occupying 70% and MA occupying 30% of the A site; Sn (tin) and Pb (lead) are at the B site, with tin and lead each occupying half; I - (Iodide ion) at the X site.

[0032] By introducing S-(2-carboxyethyl)-L-cysteine ​​molecules into the hole transport layer 2, the conductivity and chemical properties of PEDOT:PSS are improved through multi-site coordination and synergistic effects of functional groups. This effectively enhances the interfacial properties of the hole transport layer 2, promotes uniform nucleation and controllable crystallization of the perovskite precursor at the front interface, and thus improves the interfacial matching between the flexible transparent conductive substrate 1 and the narrow bandgap perovskite absorber layer 3, thereby increasing the photoelectric conversion efficiency. Meanwhile, the narrow bandgap perovskite absorber layer 3 uses the chemical formula FA. 0.7 MA 0.3 Sn 0.5 Pb 0.5 I3 perovskite materials have excellent photoelectric properties and can effectively absorb a wider spectrum of light, especially near-infrared light, thereby enhancing photoelectric performance.

[0033] In one embodiment, the thickness of the narrow bandgap perovskite absorber layer 3 is any value between 1000 nm and 1200 nm. The thickness of the hole transport layer 2 is any value between 30 nm and 50 nm. By optimizing the thicknesses of the hole transport layer 2 and the narrow bandgap perovskite absorber layer 3, the light absorption and charge transport performance of the battery can be effectively balanced, improving the photoelectric conversion efficiency and maintaining high mechanical stability. Simultaneously, it can also reduce the mechanical stress of the device and enhance the bending resistance of the flexible device.

[0034] In one embodiment, the thickness of the flexible transparent conductive substrate 1 is limited to any value between 80 μm and 150 μm to ensure that the average light transmittance of the flexible transparent conductive substrate 1 is not less than 80%, and the sheet resistance is in the range of 10 Ω / sq to 20 Ω / sq. This range can avoid the phenomenon of decreased light transmittance caused by excessive thickness of the flexible transparent conductive substrate 1, which helps to optimize the photoelectric conversion efficiency of the battery; at the same time, it also helps to improve the mechanical flexibility of the device, so that it maintains good flexibility and durability. In this embodiment or other embodiments, the flexible transparent conductive substrate 1 is preferably an ITO / PEN flexible substrate.

[0035] In one embodiment, the electron transport and hole blocking layer 4 includes an electron transport layer and a hole blocking layer. The preferred material for the electron transport layer is C. 60 By choosing C appropriately 60 The electron transport layer material helps improve electron transport efficiency, and its thickness is preferably any value between 20 nm and 30 nm. The hole blocking layer is preferably made of BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), which can form an effective hole blocking layer between the electron transport layer and the metal electrode, effectively reducing interfacial recombination losses while facilitating electron transport to the metal electrode. The thickness of this hole blocking layer is preferably any value between 6 nm and 8 nm. The thickness of the metal electrode layer 5 is preferably any value between 100 nm and 200 nm, used to ensure effective current extraction. The metal electrode layer 5 is preferably made of copper or silver. By optimizing the material and thickness parameters of each functional layer, the overall photoelectric conversion efficiency and stability of the solar cell can be effectively improved.

[0036] One embodiment provides a method for fabricating the above-mentioned flexible narrow bandgap perovskite solar cell, which specifically includes the following steps: S1. Obtain a flexible transparent conductive substrate 1, coat a PEDOT:PSS aqueous dispersion doped with SCEC onto the flexible transparent conductive substrate 1, and after coating, perform annealing treatment to form a hole transport layer 2 on the flexible transparent conductive substrate 1. S2. Prepare a perovskite precursor solution and spin-coat the perovskite precursor solution onto the hole transport layer 2 using a two-step spin-coating method. During the spin-coating process, add an anti-solvent. Then, perform stepwise annealing to form a perovskite film on the hole transport layer 2. S3. The perovskite film is subjected to back passivation treatment to form a narrow bandgap perovskite absorption layer 3 on the hole transport layer 2. S4. An electron transport layer, a hole blocking layer, and a metal electrode layer 5 are sequentially deposited on the surface of the narrow bandgap perovskite absorber layer 3 to obtain a flexible narrow bandgap perovskite solar cell doped with SCEC.

[0037] In step S2, the perovskite precursor solution is spin-coated onto the hole transport layer 2 using a two-step spin-coating method. During the spin-coating process, chlorobenzene is added as an anti-solvent, which can effectively control the crystallization process of the perovskite film and significantly improve the crystallization quality of the perovskite film. This helps to obtain a uniform and high-quality narrow bandgap perovskite absorber layer 3 in the subsequent process, thereby improving its photoelectric conversion efficiency.

[0038] In step S3, the defects in the perovskite film are effectively passivated through back passivation treatment, resulting in a high-quality narrow bandgap perovskite absorber layer 3 with fewer interface defects and non-radiative recombination, thereby enhancing the open-circuit voltage and photoelectric conversion efficiency of the solar cell.

[0039] In one embodiment, in step S1, the solid content of the PEDOT:PSS aqueous dispersion is 1%–3% to balance dispersibility, film formation, and electrical properties. Simultaneously, optimizing the solid content in the PEDOT:PSS aqueous dispersion helps control the conductivity, compositional uniformity, and film formation continuity of the hole transport layer 2, preventing the hole transport layer 2 from adversely affecting battery performance. In this embodiment or other embodiments, the annealing temperature is preferably limited to the range of 100°C to 130°C. This temperature range helps improve the film quality of the PEDOT:PSS layer, further enhancing the photoelectric performance and stability of the device.

[0040] In one embodiment, step S2, the preparation of the perovskite precursor solution includes: dissolving a raw material group comprising PbI2 (lead iodide), SnI2 (stannous iodide), MAI (methylamine iodide), and FAI (formamidine iodide) in a mixed solvent of DMF (N,N-dimethylformamide) and DMSO (dimethyl sulfoxide), stirring at room temperature for a certain period of time, and then filtering using a filter membrane. The use of the DMF / DMSO mixed solvent system helps to ensure that PbI2, SnI2, MAI, and FAI are fully dissolved in the mixed solvent, thereby ensuring the accuracy of the component ratios in the perovskite precursor solution and the uniformity and stability of the perovskite precursor solution. Simultaneously, filtration effectively removes impurities from the perovskite precursor solution, ensuring its purity. This results in a high-quality perovskite precursor solution, improving the crystallinity and photoelectric performance of the perovskite thin film, and contributing to the overall efficiency of the solar cell. In this embodiment or other embodiments, in the perovskite precursor solution prepared, the perovskite material (FA) 0.7 MA 0.3 Sn 0.5 Pb 0.5 The concentration of I3 was 2 mol / L-2.5 mol / L.

[0041] In one embodiment, step S2, the two-step annealing process includes: first, high-temperature annealing at 80°C to 120°C, followed by low-temperature annealing at 55°C to 70°C. This combination of high and low temperature annealing optimizes the crystallization process of the perovskite thin film, improves its uniformity and crystallinity, thereby enhancing photoelectric conversion efficiency and device stability. In this embodiment or other embodiments, step S2, the two-step spin coating method includes: first, low-speed spin coating at 800 rpm to 1200 rpm, followed by high-speed spin coating at 3500 rpm to 5000 rpm, with an anti-solvent added during the high-speed spin coating process. This spin coating process ensures the formation of a uniform and dense film layer on the surface of the hole transport layer 2. By adding an anti-solvent during spin coating, the DMF / DMSO mixed solvent can be rapidly evaporated, thereby inducing the perovskite crystals to grow in a more ordered manner, which helps to further improve the crystal quality and photoelectric performance of the perovskite thin film. The antisolvent is preferably chlorobenzene, and the amount added is preferably limited to the range of 500 μL to 700 μL, and the dropping rate is preferably any value between 300 μL / s and 500 μL / s.

[0042] In one embodiment, step S3, the back passivation treatment includes: spin-coating a back passivation solution onto a perovskite thin film at a rotation speed of 3000 rpm to 5000 rpm; and immediately transferring the film to a temperature of 90°C to 120°C for annealing after spin-coating. This back passivation treatment effectively passivates defects in the perovskite thin film, improves the film quality, reduces interface defects and non-radiative recombination, thereby enhancing the open-circuit voltage and photoelectric conversion efficiency of the solar cell. The back passivation solution is prepared by dissolving ethylenediamine diiodide powder in an IPA solution, and the concentration of the back passivation solution is any value between 0.5 mg / mL and 1.5 mg / mL.

[0043] Example 1 S1. A 120 μm thick ITO / PEN flexible conductive substrate was selected as the flexible transparent conductive substrate 1. After peeling off the protective film covering the surface, it was subjected to ultraviolet ozone treatment for 25 min to remove surface organic matter, resulting in a clean flexible transparent conductive substrate 1. The sheet resistance of this flexible transparent conductive substrate 1 is 15 Ω, and the average transmittance is >80%. S-(2-carboxyethyl)-L-cysteine ​​powder was dissolved in PEDOT:PSS aqueous dispersion and stirred continuously for 10 min to ensure that the S-(2-carboxyethyl)-L-cysteine ​​powder was completely dissolved and mixed evenly. Subsequently, the mixture was filtered through a 0.22 μm polytetrafluoroethylene filter membrane to obtain a PEDOT:PSS dispersion with a doping concentration of 1 mg / mL of S-(2-carboxyethyl)-L-cysteine. Then, the PEDOT:PSS mixed dispersion was spin-coated onto the surface of the flexible transparent conductive substrate 1 at a spin-coating speed of 6000 rpm. After spin-coating for 40 s, the flexible transparent conductive substrate 1 was placed on a hot plate at 110°C for annealing. After annealing for 20 min, a hole transport layer 2 with a thickness of 30 nm was formed on the flexible transparent conductive substrate 1.

[0044] S2. Dissolve 2.2 mmol lead iodide, 2.2 mmol stannous iodide, 3.08 mmol formamidine iodide, 1.32 mmol methyl iodide, 5 mmol% stannous fluoride, and 3.5 mmol% lead thiocyanate in a mixed solvent of DMF and DMSO at a volume ratio of 3:1, and stir continuously for 1 hour to ensure homogeneity. Then, filter the solution through a 0.22 μm polytetrafluoroethylene (PTFE) membrane, stirring continuously to obtain a clear and transparent perovskite precursor solution. The concentration of perovskite in this perovskite precursor solution is 2.2 mol / L. 70 μL of perovskite precursor solution was dropped onto hole transport layer 2. First, a low-speed spin coating was performed at 1000 rpm. After 10 seconds of spin coating, a high-speed spin coating was performed at 4000 rpm. At the 30th second of the high-speed spin coating, 600 μL of chlorobenzene was dropped onto hole transport layer 2, and high-speed spin coating continued. After 50 seconds of high-speed spin coating, the flexible transparent conductive substrate 1 was placed on a hot stage at 100°C for high-temperature annealing. After 10 minutes of high-temperature annealing, the flexible transparent conductive substrate 1 was transferred to a hot stage at 65°C for low-temperature annealing. After 10 minutes of low-temperature annealing, a perovskite film with a thickness of 1100 nm was formed on hole transport layer 2. The surface morphology of this perovskite film is as follows. Figure 2 (c) and Figure 3 As shown in (c), the morphology of its buried interface is as follows. Figure 4 As shown in (c), the X-ray photoelectron spectrum of the buried interface of the perovskite thin film is as follows. Figure 5 As shown in (c).

[0045] S3. Dissolve ethylenediamine diiodide powder in IPA solution and mix thoroughly to obtain a back passivation solution with a concentration of 1 mg / mL. Drop 70 μL of the back passivation solution onto the perovskite film and spin-coat at 4000 rpm for 20 s. Immediately afterwards, transfer the film to a temperature of 100 °C for annealing. After annealing for 5 min, a narrow bandgap perovskite absorber layer 3 is formed on the hole transport layer 2.

[0046] S4. Place the flexible transparent conductive substrate 1 in the thermal evaporation chamber at a depth of 4×10. -4 Under high vacuum conditions of Pa, C with a thickness of 25 nm was sequentially deposited on the surface of the narrow bandgap perovskite absorber layer 3. 60 Using materials as the electron transport layer, a 6nm thick BCP as the hole blocking layer, and a 100nm thick copper as the metal electrode layer 5, a flexible narrow bandgap perovskite solar cell with an inverted pin structure and SCEC-doped was obtained.

[0047] Example 2 The difference between this embodiment and Embodiment 1 is that the annealing temperature in step S1 is 100°C. A flexible narrow-bandgap perovskite solar cell doped with SCEC is finally obtained.

[0048] Example 3 The difference between this embodiment and Embodiment 1 is that the annealing temperature in step S1 is 130°C. A flexible narrow-bandgap perovskite solar cell doped with SCEC is finally obtained.

[0049] Example 4 The difference between this embodiment and Embodiment 1 is that, in step S1, the doping concentration of S-(2-carboxyethyl)-L-cysteine ​​in the PEDOT:PSS dispersion is 2 mg / mL. A flexible narrow-bandgap perovskite solar cell doped with SCEC was ultimately obtained.

[0050] Example 5 The difference between this embodiment and Example 1 is that, in step S1, the doping concentration of S-(2-carboxyethyl)-L-cysteine ​​in the PEDOT:PSS dispersion is 0.5 mg / mL. A flexible narrow-bandgap perovskite solar cell doped with SCEC was finally obtained.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that, in step S1, the PEDOT:PSS dispersion did not contain S-(2-carboxyethyl)-L-cysteine. The perovskite film obtained in step S2 has the following surface morphology. Figure 2 (a) and Figure 3 As shown in (a), the morphology of its buried interface is as follows. Figure 4As shown in (a), the X-ray photoelectron spectrum of the buried interface of the perovskite thin film is as follows. Figure 5 As shown in (a), a flexible narrow-bandgap perovskite solar cell was finally fabricated.

[0052] Comparative Example 2 The difference between this comparative example and Example 1 is that in step S1, the PEDOT:PSS dispersion is doped with the monocarboxylic acid cysteine ​​(Cys), and the doping concentration of monocarboxylic acid cysteine ​​is 1 mg / mL. The perovskite film obtained in step S2 has the following surface morphology. Figure 2 (b) and Figure 3 As shown in (b), the morphology of its buried interface is as follows. Figure 4 As shown in (b), the X-ray photoelectron spectrum of the buried interface of the perovskite thin film is as follows. Figure 5 As shown in (b), a flexible narrow-bandgap perovskite solar cell was finally fabricated.

[0053] Depend on Figure 2 and Figure 3 It can be seen that the perovskite films prepared in Example 1, as well as Comparative Examples 1 and 2, all exhibit good coverage. However, compared to the perovskite films prepared in Comparative Examples 1 and 2, the perovskite film prepared in Example 1 shows a more uniform and denser surface morphology, with increased grain size, clearer boundaries, and a significant reduction in local defects and inhomogeneous regions. This indicates that the incorporation of S-(2-carboxyethyl)-L-cysteine ​​can effectively regulate the surface energy and chemical environment of the battery front interface, thereby improving the spreading behavior of the perovskite material at the front interface and promoting uniform nucleation and ordered crystallization of the perovskite film.

[0054] The perovskite films prepared in step S2 of Example 1, Comparative Examples 1 and 2 were peeled off from the hole transport layer 2, and the morphology of their buried interface was examined, i.e., the end face of the perovskite film that is attached to the hole transport layer 2. The examination results are as follows: Figure 4 As shown.

[0055] Depend on Figure 4 It is evident that the perovskite film formed on the surface of the SCEC-doped hole transport layer 2 exhibits more uniform and complete coverage at the buried interface, tighter interfacial contact, and a significantly larger grain size. This indicates that SCEC doping significantly improves the interfacial matching between PEDOT:PSS and the narrow-bandgap Sn-Pb perovskite. Furthermore, it confirms that the dicarboxyl groups and other polar functional groups in the SCEC molecule can enhance the interaction at the front interface, reduce the accumulation of interfacial defects, and provide a more favorable interfacial foundation for subsequent charge transport.

[0056] X-ray photoelectron spectroscopy (XPS) was performed on the buried interface of the perovskite thin films prepared in step S2 of Example 1, Comparative Examples 1 and 2. The results are as follows: Figure 5 As shown.

[0057] Depend on Figure 5 As can be seen from (a), (b), and (c), in the perovskite thin film prepared in Example 1, Sn 4+ / Sn 2+ The proportion was 18.8%, significantly lower than the 47.3% in the perovskite film prepared in Comparative Example 1 and the 34% in the perovskite film prepared in Comparative Example 2. This indicates that the SCEC-doped hole transport layer 2 can more effectively suppress Sn at the buried interface of the perovskite film. 2+ To Sn 4+ The oxidation of Sn was observed. This result verifies that the dicarboxyl group and other polar functional group structures of SCEC can form stronger interactions with Sn-related defect sites at the hole transport layer 2 / perovskite 3 interface through multi-site coordination, thereby effectively modulating the chemical environment of the buried interface and inhibiting Sn oxidation. 2+ The oxidation of the metal and the formation of Sn vacancies reduce the density of trapped states at the interface. This helps to reduce nonradiative recombination losses and improve the efficiency of interface charge extraction and transport.

[0058] The steady-state photoluminescence properties of the perovskite films prepared in step S2 of Example 1, Comparative Examples 1 and 2 were tested, and the test results are as follows: Figure 6 As shown.

[0059] Depend on Figure 6 As shown in (a), under top-incidence conditions, the perovskite film prepared in Example 1 exhibits the highest steady-state photoluminescence (PL) intensity, and the emission peak position is blue-shifted from approximately 990 nm in the perovskite film prepared in Comparative Example 1 to 988 nm. This indicates that the SCEC-doped hole transport layer 2 helps improve the overall crystallinity of the narrow-bandgap perovskite film and reduces nonradiative recombination caused by bulk defects. Figure 6 As shown in (b), under bottom-incidence conditions, the perovskite film prepared in Example 1 exhibits the most significant steady-state photoluminescence quenching, with the peak position further blue-shifted to 981 nm. In contrast, the perovskite films prepared in Comparative Examples 1 and 2 have peak positions of approximately 989 nm and 988 nm, respectively. Since bottom-incidence testing is more sensitive to the PEDOT:PSS / perovskite buried interface, the above results indicate that SCEC can more effectively optimize the energy matching and defect state of the buried interface, enhance hole extraction, and reduce non-radiative recombination at the interface, thereby promoting the separation and transport of photogenerated carriers at the buried interface.

[0060] The performance of the SCEC-doped flexible narrow-bandgap perovskite solar cells prepared in Examples 1-5 and the flexible narrow-bandgap perovskite solar cells prepared in Comparative Examples 1-2 were tested, and the test results are as follows: Figures 7-10 And as shown in Table 1.

[0061]

[0062] From Table 1 and Figure 7 As can be seen, compared with the flexible narrow-bandgap perovskite solar cells prepared in Comparative Examples 1 and 2, the flexible narrow-bandgap perovskite solar cell prepared in Example 1 shows significant improvements in key performance parameters such as open-circuit voltage, short-circuit current density, fill factor, and photoelectric conversion efficiency. Furthermore, compared with the cysteine-doped flexible narrow-bandgap perovskite solar cell in Comparative Example 2, the SCEC-doped flexible narrow-bandgap perovskite solar cell also exhibits higher efficiency and better charge transport characteristics. This indicates that by doping S-(2-carboxyethyl)-L-cysteine ​​(SCEC) into the hole transport layer 2, the contact and charge transport conditions of the front interface of the flexible device can be effectively improved, thereby enhancing the overall photovoltaic performance of the device. This is mainly attributed to the fact that the dicarboxyl groups and other polar functional groups in the SCEC molecule can enhance the interfacial interaction between the hole transport layer 2 and the narrow-bandgap Sn-Pb perovskite, regulate the conductivity and chemical properties of PEDOT:PSS, improve the wetting and spreading properties of the front interface, and promote the uniform nucleation and ordered crystallization of the perovskite film at the interface. Furthermore, SCEC can reduce the defect density at the buried interface and suppress non-radiative recombination losses, thereby achieving a synergistic improvement in various performance parameters. Simultaneously, by Figure 8 It can be seen that, compared with the flexible narrow-bandgap perovskite solar cell prepared in Comparative Example 1, the SCEC-doped flexible narrow-bandgap perovskite solar cell prepared in Example 1, due to the doping of SCEC in the hole transport layer 2, can effectively improve the current density and voltage output of the cell, thereby improving its photoelectric conversion efficiency and overall cell performance. Figure 9 It can be seen that, compared with the flexible narrow-bandgap perovskite solar cell prepared in Comparative Example 1, the hole transport layer 2 doped with SCEC can significantly improve the photoelectric conversion efficiency of the cell, especially in the wide wavelength range, where SCEC doping effectively enhances the generation and extraction efficiency of photogenerated carriers. Figure 10 As shown in (a), the flexible narrow-bandgap perovskite solar cell prepared in Comparative Example 1 exhibits a significant hysteresis phenomenon, while... Figure 10As shown in (b), the hysteresis phenomenon of the SCEC-doped flexible narrow bandgap perovskite solar cell prepared in Example 1 is significantly smaller, which indicates that its forward and reverse scanning differences are smaller and its output stability is enhanced. This further illustrates that SCEC doping helps to improve interface compatibility and reduce charge retention, thereby reducing the hysteresis effect and improving the overall performance and stability of the cell.

[0063] As shown in Table 1, the overall performance of the flexible narrow-bandgap perovskite solar cell prepared in Example 1 is superior to that prepared in Examples 2-5. Comparing the performance of the flexible narrow-bandgap perovskite solar cells prepared in Example 1 with those prepared in Examples 2 and 3, it is evident that the flexible narrow-bandgap perovskite solar cell exhibits the best overall performance when the annealing temperature is around 110°C. This indicates that the annealing temperature in step S1 has a significant impact on the performance of the final flexible narrow-bandgap perovskite solar cell. This is mainly because the annealing temperature not only affects the removal of moisture and residual solvent from the hole transport layer 2 (i.e., the PEDOT:PSS film), but also significantly affects the film's density, surface morphology, conductivity, and adhesion to the flexible transparent conductive substrate 1. An appropriate annealing temperature can promote the rearrangement of polymer chains within the PEDOT:PSS film, making the film structure more uniform and ordered, thereby improving hole transport efficiency and interfacial charge extraction capability. Meanwhile, an appropriate annealing temperature can also improve the surface smoothness and interfacial wettability of the hole transport layer 2, providing good pre-interfacial conditions for the uniform film formation of the subsequent narrow bandgap perovskite absorber layer 3. Comparing the performance of the flexible narrow bandgap perovskite solar cells prepared in Examples 1, 4, and 5, it can be seen that the overall performance of the prepared flexible narrow bandgap perovskite solar cell is optimal when the doping concentration of S-(2-carboxyethyl)-L-cysteine ​​(SCEC) is approximately 1 mg / mL. Therefore, it can be concluded that the doping concentration of S-(2-carboxyethyl)-L-cysteine ​​(SCEC) in step S1 also has a significant impact on the performance of the finally prepared flexible narrow bandgap perovskite solar cell. This is mainly because the change in the doping concentration of SCEC in the hole transport layer 2 affects the chemical environment, wettability, conductivity, number of interfacial interaction sites on the surface of the hole transport layer 2, and its interfacial bonding ability with the flexible transparent conductive substrate 1 and the narrow bandgap perovskite absorber layer 3. An appropriate doping concentration can fully leverage the multi-site effect of SCEC's dicarboxyl groups, improving the wettability and interfacial compatibility of the front interface, promoting uniform nucleation and dense crystallization of the perovskite material, and passivating defects at the front interface, thereby improving carrier extraction efficiency and photovoltaic performance. If the SCEC doping concentration is too low, the modification of the hole transport layer 2 surface is not significant, and the control over the front interface chemical environment and surface energy is limited. This leads to insufficient improvement in the interface matching between the hole transport layer 2 and the narrow bandgap perovskite absorber layer 3, resulting in a weak improvement in the perovskite film quality, interface defect passivation, and charge extraction, and ultimately, insignificant improvement in battery performance. If the SCEC doping concentration is too high, excessive SCEC molecules may affect the continuity, uniformity, and conductivity of the PEDOT:PSS film itself, leading to local compositional inhomogeneity on the surface of the hole transport layer 2, which is detrimental to uniform perovskite film formation and interfacial charge transport, ultimately causing a decrease in battery performance.

[0064] The flexible narrow-bandgap perovskite solar cell doped with SCEC prepared in Example 1 and the flexible narrow-bandgap perovskite solar cell prepared in Comparative Example 1 were used as bottom sub-cells, and were stacked and integrated with a composite connecting layer and a flexible 1.77 eV wide-bandgap perovskite top sub-cell to form a flexible two-sided all-perovskite tandem solar cell (referred to as the experimental group) and a control flexible all-perovskite tandem solar cell (referred to as the control group). The performance of the flexible two-sided all-perovskite tandem solar cell and the control flexible all-perovskite tandem solar cell were tested. The test results are as follows: Figure 11 and Figure 12 As shown in the figure. In this flexible, two-sided all-perovskite tandem solar cell, the bottom sub-cell is denoted as NBG, and the top sub-cell is denoted as WBG.

[0065] Depend on Figure 11 It can be seen that the control group achieved a power conversion efficiency of 25.21% during the voltage scan, with an open-circuit voltage of 2.143V and a short-circuit current density of 14.75mA / cm². 2 The fill factor was 79.4%. The experimental group achieved a power conversion efficiency of 26.95% during the voltage scan, with an open-circuit voltage of 2.167V and a short-circuit current density of 15.08mA / cm². 2 The fill factor is 82.4%. This indicates that SCEC doping can improve the photovoltaic performance of flexible tandem perovskite solar cells by enhancing the performance of flexible single-junction narrow-bandgap perovskites.

[0066] Depend on Figure 12 It can be seen that the short-circuit current density of the top and bottom sub-cells of this flexible, two-sided perovskite tandem solar cell is 14.48 mA / cm². 2 and 15.20 mA / cm 2 This indicates that the current density matching between the two sub-cells is good after the SCEC-doped hole transport layer 2 is applied. Therefore, the front-interface modulation strategy of the SCEC-doped hole transport layer 2 provided in this application is not only applicable to flexible single-junction narrow-bandgap perovskite devices, but can also be further extended to flexible all-perovskite tandem solar cells.

[0067] In summary, the SCEC-doped flexible narrow-bandgap perovskite solar cell provided in this application, by introducing SCEC into the hole transport layer 2, can effectively improve the wetting, spreading, and interfacial bonding performance of the front interface, promote the uniform crystallization of the narrow-bandgap perovskite film, enhance the contact of the buried interface and passivate defects at the front interface, thereby improving the carrier extraction and transport efficiency and reducing non-radiative recombination. This results in a significant improvement in the performance of the flexible narrow-bandgap perovskite solar cell and provides good technical support for its application in flexible all-perovskite tandem solar cells.

[0068] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A flexible narrow-bandgap perovskite solar cell doped with SCEC, characterized in that, It includes a flexible transparent conductive substrate, a hole transport layer, a narrow bandgap perovskite absorption layer, an electron transport layer, a hole blocking layer, and a metal electrode layer, which are stacked sequentially from bottom to top. The hole transport layer is made of PEDOT:PSS doped with SCEC, and the doping amount of SCEC is 1 mg / mL to 2 mg / mL compared to the PEDOT:PSS aqueous dispersion. The chemical formula of the narrow bandgap perovskite absorber layer is FA. 0.7 MA 0.3 Sn 0.5 Pb 0.5 I3.

2. The flexible narrow bandgap perovskite solar cell as described in claim 1, characterized in that, The thickness of the narrow bandgap perovskite absorber layer is any value between 1000 nm and 1200 nm; The thickness of the hole transport layer is any value between 30nm and 50nm.

3. The flexible narrow bandgap perovskite solar cell as described in claim 2, characterized in that, The thickness of the flexible transparent conductive substrate is any value between 80μm and 150μm to ensure that the average light transmittance of the flexible transparent conductive substrate is not less than 80% and the sheet resistance is in the range of 10Ω / sq to 20Ω / sq.

4. The flexible narrow bandgap perovskite solar cell as described in claim 2, characterized in that, The electron transport layer is made of C. 60 The thickness is any value between 20nm and 30nm; The hole blocking layer is made of BCP and has a thickness of any value between 6nm and 8nm. The thickness of the metal electrode layer is any value between 100 nm and 200 nm.

5. The method for fabricating a flexible narrow bandgap perovskite solar cell according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Obtain a flexible transparent conductive substrate, coat the flexible transparent conductive substrate with a PEDOT:PSS aqueous dispersion doped with SCEC, and after coating, perform annealing treatment to form a hole transport layer on the flexible transparent conductive substrate. S2. Prepare a perovskite precursor solution, spin-coat the perovskite precursor solution onto the hole transport layer using a two-step spin-coating method, and add antisolvent during the spin-coating process. Then, perform stepwise annealing to form a perovskite film on the hole transport layer. S3. Perform back passivation treatment on the perovskite film to form a narrow bandgap perovskite absorption layer on the hole transport layer; S4. An electron transport layer, a hole blocking layer, and a metal electrode layer are sequentially deposited on the surface of the narrow bandgap perovskite absorber layer to obtain a flexible narrow bandgap perovskite solar cell doped with SCEC.

6. The preparation method according to claim 5, characterized in that, In step S1, the solid content of the PEDOT:PSS aqueous dispersion is 1%–3%; the annealing temperature is 100℃–130℃.

7. The preparation method according to claim 5, characterized in that, In step S2, the preparation of the perovskite precursor solution includes: dissolving the raw material group including PbI2, SnI2, MAI and FAI in a DMF / DMSO mixed solvent, stirring at room temperature for a certain period of time, and then filtering using a filter membrane; The concentration of perovskite material in the perovskite precursor solution is any value between 2 mol / L and 2.5 mol / L.

8. The preparation method according to claim 5, characterized in that, In step S2, the two-step annealing process includes: high-temperature annealing at a temperature of 80℃~120℃, and then low-temperature annealing at a temperature of 55℃~70℃.

9. The preparation method according to claim 5, characterized in that, In step S2, the two-step spin coating method includes: first, low-speed spin coating at a speed of 800 rpm to 1200 rpm, and then high-speed spin coating at a speed of 3500 rpm to 5000 rpm. During the high-speed spin coating process, an anti-solvent is added dropwise, and the amount of anti-solvent added is 500 μL to 700 μL, with a drop rate of 300 μL / s to 500 μL / s.

10. The preparation method according to claim 5, characterized in that, In step S3, the back passivation treatment includes: spin-coating the back passivation solution onto the perovskite film at a rotation speed of 3000 rpm to 5000 rpm, and immediately transferring it to a temperature of 90℃ to 120℃ for annealing after spin-coating. The back passivation solution is prepared by dissolving ethylenediamine diiodide powder in IPA solution, and the concentration of the back passivation solution is any value between 0.5 mg / mL and 1.5 mg / mL.

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