Cs2agbibr6 thin film with controllable particle size, preparation method and solar cell

Abstract

The application relates to a Cs2AgBiBr6 thin film with controllable particle size, a preparation method and a solar cell, and the raw materials of the thin film include CsBr, AgBr, BiBr3 and AgSCN; wherein the molar ratio of CsBr, AgBr and BiBr3 is 2:1:1; the molar ratio of AgBr and AgSCN is 100:(3-12). The Cs2AgBiBr6 thin film with large particle size, controllable particle size, good crystallinity and compactness and uniformity is prepared by taking AgSCN as an additive and changing the amount of the additive, the crystal boundary of the thin film is reduced, meanwhile, the crystal boundary defects are passivated, which is helpful to inhibit the recombination loss of carriers at the crystal boundary, promote the transmission and separation of the carriers, reduce the carrier transmission potential barrier and improve the photovoltaic performance of the cell; the solar cell device assembled from the Cs2AgBiBr6 thin film has obviously improved photoelectric conversion efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of solar cells, and in particular relates to a Cs2AgBiBr6 thin film with controllable particle size, a preparation method and a solar cell. Background Art

[0002] Organic-inorganic hybrid lead-based perovskites (APbX3, where A is an organic cation and X is a halogen) have made rapid progress in the photovoltaic field, achieving power conversion efficiencies (PCEs) exceeding 26%, comparable to commercial silicon solar cells. However, their poor stability due to their chemical composition and lead toxicity have limited their further commercial application.

[0003] Silver (Ag) and bismuth (Bi) are used to replace Pb (2Pb 2+ →B + + Bi 3+ ) can produce a non-toxic and stable double perovskite material (Cs2AgBiX6). Research has shown that Bi-based double perovskites exhibit similar optoelectronic properties to lead-based perovskites, such as high absorption coefficient, long carrier lifetime, and high mobility, and hold great potential for development in wide-bandgap and transparent photovoltaics. However, the poor film quality and numerous defects of multi-component Cs2AgBiX6 have led to poor photovoltaic performance, limiting its further development. Besides the significant impact of defects on photovoltaic performance, excessive ion migration increases interfacial impedance, reducing the cell's fill factor, thereby impacting battery performance. Furthermore, defects caused by ion migration can accelerate battery performance degradation. Furthermore, conventional Cs2AgBiBr6 thin films typically have a small particle size, resulting in numerous grain boundaries and defects. This poor film quality and crystallinity lead to high non-radiative recombination and interfacial resistance, low carrier transport and collection efficiency, and poor photovoltaic performance and material stability. Furthermore, grain boundaries are primary pathways for ion migration, and excessive ion migration can also lead to excessive ion migration. Therefore, designing and preparing a Cs2AgBiBr6 thin film with large and controllable particle size and reduced ion migration is of great significance for improving its photovoltaic performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned technical deficiencies, provide a Cs2AgBiBr6 thin film with controllable particle size, a preparation method and a solar cell, and solve the technical problems of small particle size, poor film forming properties and poor photovoltaic performance of Cs2AgBiX6 in the prior art.

[0005] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0006] In a first aspect, the present invention provides a Cs2AgBiBr6 thin film with controllable particle size, the raw materials of which include CsBr, AgBr, BiBr3 and AgSCN; wherein the molar ratio of CsBr, AgBr and BiBr3 is 2:1:1; and the molar ratio of AgBr and AgSCN is 100:(3~12).

[0007] In a second aspect, the present invention provides a method for preparing a Cs2AgBiBr6 thin film with controllable particle size, comprising the following steps:

[0008] (1) adding CsBr, AgBr, BiBr3 and AgSCN to a first solvent and stirring until all solids are dissolved to obtain a mixed solution; wherein the molar ratio of CsBr:AgBr:BiBr3 is 2:1:1, and the molar ratio of AgBr to AgSCN is 100:(3-12);

[0009] (2) The mixed solution undergoes a hydrothermal reaction to obtain Cs2AgBiBr6 crystals;

[0010] (3) dissolving the Cs2AgBiBr6 crystals in a second solvent to obtain a Cs2AgBiBr6 precursor solution;

[0011] (4) The Cs2AgBiBr6 precursor solution is coated on the substrate, thermally annealed in an inert gas atmosphere, and naturally cooled to room temperature to obtain a Cs2AgBiBr6 film with controllable particle size.

[0012] In a third aspect, the present invention provides a solar cell comprising an FTO glass conductive substrate, a TiO2 electron transport layer, an absorption layer and a carbon top electrode stacked in sequence; the absorption layer adopts the above-mentioned Cs2AgBiBr6 thin film.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The present invention provides a Cs2AgBiBr6 thin film, which is prepared by using AgSCN as an additive and changing the amount of the additive to obtain a Cs2AgBiBr6 thin film with large particle size, controllable particle size, good crystallinity, and dense and uniformity, wherein the additionally added Ag + and SCN - It can passivate Ag and Br defects, and compared with Br - , SCN - With Ag + and Bi 3+The binding force is stronger, which can inhibit the migration of metal ions; the presence of large particle size reduces the grain boundaries of the film, and at the same time the grain boundary defects are passivated, which helps to inhibit the recombination loss of carriers at the grain boundaries, promotes the transport and separation of carriers, reduces the carrier transport barrier, and is beneficial to improving the photovoltaic performance of the cell; the solar cell device assembled from the Cs2AgBiBr6 film has a significantly improved photoelectric conversion efficiency of 1.74~2.95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Comparative scanning electron microscope morphologies of the Cs2AgBiBr6 thin film prepared in Comparative Example 1 and the Cs2AgBiBr6 thin films prepared in Examples 1-4; (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, (d) is Example 3, and (e) is Example 4;

[0016] Figure 2 The particle size distribution diagrams of the Cs2AgBiBr6 thin film prepared in Comparative Example 1 and the Cs2AgBiBr6 thin films prepared in Examples 1-4; wherein (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, (d) is Example 3, and (e) is Example 4;

[0017] Figure 3 Schematic diagram of the Cs2AgBiBr6 battery structure in an embodiment of the present invention;

[0018] Figure 4 Comparison of the current-voltage curves of the solar cells of Comparative Example 1 and Examples 5-8;

[0019] Figure 5 Box diagram of various parameters of solar cell devices of comparative examples 1 and 5-8; wherein (a) is V oc (open circuit voltage), (b) is J sc (short-circuit current density), (c) FF (fill factor), and (d) PCE (photovoltaic conversion efficiency). DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] The present invention proposes a method and application of preparing a Cs2AgBiBr6 thin film with large and controllable particle size by a chemical modification method. By optimizing the amount of additives added, a Cs2AgBiBr6 thin film with good crystallinity, density and uniformity is obtained. The Cs2AgBiBr6 thin film prepared by this method effectively increases the grain size of the film and has a controllable particle size. While reducing grain boundary defects, it also ensures crystal density, helps to suppress the recombination loss of carriers at the grain boundaries and improves the photovoltaic performance of the battery. Among them, the additionally added Ag + and SCN - Can passivate Ag and Br defects; at the same time compared to Br - , SCN - With Ag + and Bi 3+ The stronger the binding force, the more it can inhibit the migration of metal ions. Ultimately, the dual effects of AgSCN passivating defects and inhibiting ion migration jointly improve the photovoltaic performance of the cell.

[0022] In a first aspect, the present invention provides a Cs2AgBiBr6 film with controllable particle size, the raw materials of which include CsBr, AgBr and BiBr3 in a stoichiometric ratio; and also include AgSCN accounting for 3 to 12% of the molar amount of AgBr.

[0023] Preferably, in the Cs2AgBiBr6 thin film, the grain size is between 500 nm and 1000 nm, including but not limited to 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, etc.

[0024] By designing a large-particle Cs2AgBiBr6 film, the present invention helps reduce grain boundaries and defects, improving film quality and crystallinity, thereby reducing non-radiative recombination and interface resistance, improving carrier transport and collection efficiency, and enhancing photovoltaic performance and material stability. Furthermore, grain boundaries are also the main channels for ion migration, and increasing particle size and reducing grain boundaries are also important ways to inhibit ion migration. In summary, by optimizing grain size, the overall performance and durability of double perovskite solar cells can be significantly enhanced.

[0025] The present invention facilitates the preparation of a Cs2AgBiBr6 thin film with adjustable particle size by adding AgSCN and controlling the addition amount thereof.

[0026] In a second aspect, the present invention provides a method for preparing a Cs2AgBiBr6 thin film with controllable particle size, comprising the following steps:

[0027] (1) adding CsBr, AgBr, BiBr3 and AgSCN into a first solvent, stirring until the solids are all dissolved to obtain a mixed solution; wherein the molar ratio of CsBr:AgBr:BiBr3 is 2:1:1, and the molar amount of AgSCN is 3-12% of the molar amount of AgBr;

[0028] (2) preparing a Cs2AgBiBr6 crystal through a hydrothermal reaction of the mixed solution;

[0029] (3) dissolving the Cs2AgBiBr6 crystal in a second solvent to obtain a Cs2AgBiBr6 precursor solution;

[0030] (4) coating the Cs2AgBiBr6 precursor solution onto a substrate, performing a thermal annealing treatment under an inert gas atmosphere, and naturally cooling to room temperature to obtain a Cs2AgBiBr6 film with controllable particle size.

[0031] Preferably, the molar concentration of CsBr in the mixed solution of step (1) is 0.03-1.2 mol / L; more preferably, 0.03-0.2 mol / L, including but not limited to 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, etc.

[0032] Preferably, in step (1), the first solvent is an HBr aqueous solution with a mass concentration of 46-50%, and the concentration includes but is not limited to 46%, 47%, 48%, 49%, 50%, etc.

[0033] Preferably, in step (1), the stirring until the solids are all dissolved is performed at 75-85 ℃ for 20 min-120 min; wherein the temperature includes but is not limited to 75 ℃, 76 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, etc.; and the stirring time includes but is not limited to 20 min, 30 min, 40 min, 50 min, 55 min, 60 min, 65 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc.

[0034] Preferably, in step (2), the hydrothermal reaction is carried out at 130°C to 200°C for 2 to 4 hours, wherein the reaction temperature includes but is not limited to 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, etc.; the reaction time includes but is not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, etc.

[0035] Preferably, in step (3), the concentration of the Cs2AgBiBr6 precursor solution is 0.46 to 0.54 mmol / mL; including but not limited to 0.46 mmol / mL, 0.47 mmol / mL, 0.48 mmol / mL, 0.49 mmol / mL, 0.50 mmol / mL, 0.51 mmol / mL, 0.52 mmol / mL, 0.53 mmol / mL, 0.54 mmol / mL, etc.

[0036] Preferably, in step (3), the second solvent is dimethyl sulfoxide (DMSO).

[0037] Preferably, in step (3), Cs2AgBiBr6 crystals are dissolved in a second solvent and stirred at 60°C and 800-1200 r / min for 30-120 minutes to obtain a Cs2AgBiBr6 precursor solution.

[0038] Preferably, in step (4), the Cs2AgBiBr6 precursor solution is deposited on the substrate by spin coating, the rotation speed in the spin coating is 500-3000 rpm, and the spin coating time is 35-60s; the thermal annealing treatment is annealing at 200℃-300℃ for 5-10 min; wherein the rotation speed includes but is not limited to 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm, 8000 rpm, 9000 rpm, 10000 rpm, 120 ... rpm, etc.; rotation time includes but is not limited to 35s, 40s, 45s, 50s, 55s, 60s, etc.; thermal annealing temperature includes but is not limited to 200°C, 220°C, 240°C, 250°C, 260°C, 280°C, 285°C, 290°C, 300°C, etc.; thermal annealing time includes but is not limited to 5min, 6min, 7min, 8min, 9min, 10 min, etc.

[0039] In a third aspect, the present invention provides a solar cell comprising an FTO glass conductive substrate, a TiO2 electron transport layer, an absorption layer and a carbon top electrode stacked in sequence; the absorption layer adopts the above-mentioned Cs2AgBiBr6 thin film.

[0040] Preferably, the thickness of the TiO2 electron transport layer is 60-100 nm; the thickness of the absorption layer is 300-350 nm; and the thickness of the carbon top electrode is 1.5-1.8 μm.

[0041] In a fourth aspect, the present invention provides a method for preparing a solar cell, comprising the following steps:

[0042] S1, cleaning FTO conductive glass;

[0043] S2, preparation of TiO2 electron transport layer on FTO conductive glass;

[0044] S3, preparing a Cs2AgBiBr6 thin film: first prepare a Cs2AgBiBr6 precursor solution, then spin-coat it on the TiO2 electron transport layer, perform thermal annealing in an inert gas atmosphere, and naturally cool to room temperature to obtain a Cs2AgBiBr6 thin film with good crystallinity;

[0045] S4, prepare a carbon top electrode on the Cs2AgBiBr6 film.

[0046] Preferably, in step S1, the FTO conductive glass is cleaned as follows: ultrasonically washing the FTO conductive glass substrate for 30 minutes using a washing process of distilled water and detergent (volume ratio: 1:100), distilled water, acetone, isopropyl alcohol, and anhydrous ethanol, in sequence. The FTO conductive glass substrate is then air-dried under a nitrogen atmosphere for later use.

[0047] Preferably, in step S2, the TiO2 electron transport layer is prepared as follows: 80 μL of a c-TiO2 precursor is spin-coated on the treated FTO substrate at 7000 rpm for 30 s, followed by heat treatment at 500°C in air for 2 h to form a dense TiO2 (c-TiO2) layer. A mesoporous TiO2 (m-TiO2) layer is deposited by spin-coating a TiO2 colloid (2000 rpm for 30 s) and heat-treating at 450°C in air for 30 min.

[0048] Preferably, in step S4, the carbon top electrode is prepared as follows: a mask is attached to the Cs2AgBiBr6 film, carbon conductive paste is applied, and annealing is performed at 100°C for 10 min.

[0049] The present invention is further described in detail below through specific examples.

[0050] Example 1 (Cs2AgBiBr6 thin film)

[0051] A method for preparing a Cs2AgBiBr6 thin film with controllable particle size, comprising the following steps:

[0052] (1) Add 8 mmol CsBr, 4 mmol BiBr3, 4 mmol AgBr, 0.12 mmol AgSCN, and 60 mL HBr (48%) aqueous solution into a 100 mL polytetrafluoroethylene reactor and stir at 80 °C for 1 h until all the solids are dissolved.

[0053] (2) Place the inner container in step (1) into a reactor, react in an oven at 130 °C for 2 h, and then cool naturally to room temperature to obtain red stable Cs2AgBiBr6 crystals;

[0054] (3) 0.5 mmol of the Cs2AgBiBr6 crystals prepared in step (2) was dissolved in 1000 μL of DMSO and stirred at 60°C and 1000 rpm for 30 min to obtain a clear, transparent and stable yellow Cs2AgBiBr6 precursor solution;

[0055] (4) The Cs2AgBiBr6 precursor solution prepared in step (3) is deposited on the FTO glass substrate by spin coating. Specifically, the FTO glass substrate is fixed on the spin coater, and 40 μL of the Cs2AgBiBr6 precursor solution is drop-coated on the FTO glass substrate. After the solution is completely spread, the spin coater is started at a speed of 3000 rpm and the spin coating is performed for 60 seconds. The film is then annealed at 285°C for 5 minutes under an inert gas atmosphere to obtain a Cs2AgBiBr6 film with good crystallinity (such as Figure 1 (b) and Figure 2 (b)).

[0056] Example 2 (Cs2AgBiBr6 thin film)

[0057] A method for preparing a Cs2AgBiBr6 thin film with controllable particle size, which differs from Example 1 only in that the amount of AgSCN is adjusted to 0.24 mmol, and the other steps and conditions are the same as those in Example 1, to obtain a Cs2AgBiBr6 thin film with good crystallinity (such as Figure 1 (c) and Figure 2 (c)).

[0058] Example 3 (Cs2AgBiBr6 thin film)

[0059] A method for preparing a Cs2AgBiBr6 thin film with controllable particle size, which differs from Example 1 only in that the amount of AgSCN is adjusted to 0.36 mmol, and the other steps and conditions are the same as those in Example 1, to obtain a Cs2AgBiBr6 thin film with good crystallinity (such as Figure 1 (d) and Figure 2 (d)).

[0060] Example 4 (Cs2AgBiBr6 thin film)

[0061] A method for preparing a Cs2AgBiBr6 thin film with controllable particle size, which differs from Example 1 only in that the amount of AgSCN is adjusted to 0.48 mmol, and the other steps and conditions are the same as those in Example 1, to obtain a Cs2AgBiBr6 thin film with good crystallinity (such as Figure 1 (e) and Figure 2 (e)).

[0062] Example 5 (Solar Cell)

[0063] A Cs2AgBiBr6 solar cell, such as Figure 3 As shown, the specific structure includes, arranged in order from bottom to top: FTO glass conductive substrate, TiO2 electron transport layer, Cs2AgBiBr6 absorption layer film, and carbon top electrode.

[0064] The specific preparation of the Cs2AgBiBr6 solar cell includes the following steps:

[0065] S1. The FTO conductive glass was cleaned as follows: the washing steps were followed by ultrasonic washing for 30 minutes in a distilled water and detergent volume ratio of 1:100, followed by distilled water, acetone, isopropyl alcohol, and anhydrous ethanol. The FTO conductive glass substrate was then air-dried for later use. The thickness of the FTO layer was approximately 600 nm.

[0066] S2. Preparation of a TiO2 electron transport layer (80 nm): Spin-coat 80 μL of a 0.15 g / mL c-TiO2 ethanol solution onto an FTO conductive glass substrate at 7000 rpm for 30 s. The substrate was then calcined at 500°C in air for 2 h to form a c-TiO2 layer. Spin-coat 80 μL of a 12.5 g / mL m-TiO2 ethanol solution onto the c-TiO2 layer at 2000 rpm for 30 s. The substrate was then calcined at 450°C in air for 30 min to form an m-TiO2 layer, thereby forming a TiO2 electron transport layer.

[0067] S3. Preparing a Cs2AgBiBr6 absorption layer film (320 nm) on the TiO2 electron transport layer, the specific steps are the same as those in Example 1 (i.e., the FTO glass substrate is replaced with the TiO2 electron transport layer);

[0068] S4. Brush coating of the C top electrode (1.6 μm): A suitable mask was made on the Cs2AgBiBr6 absorption layer, and the C electrode was prepared by manual brush coating and annealing at 100 °C for 10 min. At this point, the complete Cs2AgBiBr6 solar cell was prepared.

[0069] Example 6 (Solar Cell)

[0070] A Cs2AgBiBr6 solar cell differs from Example 5 only in that 0.24 mmol of AgSCN is used in the Cs2AgBiBr6 absorption layer film, that is, the Cs2AgBiBr6 absorption layer film is prepared according to the steps of Example 2; other steps and conditions are the same as those in Example 5.

[0071] Example 7 (Solar Cell)

[0072] A Cs2AgBiBr6 solar cell differs from Example 5 only in that 0.36 mmol of AgSCN is used in the Cs2AgBiBr6 absorption layer film, that is, the Cs2AgBiBr6 absorption layer film is prepared according to the steps of Example 3; other steps and conditions are the same as those in Example 5.

[0073] Example 8 (Solar Cell)

[0074] A Cs2AgBiBr6 solar cell differs from Example 5 only in that 0.48 mmol of AgSCN is used in the Cs2AgBiBr6 absorption layer film, that is, the Cs2AgBiBr6 absorption layer film is prepared according to the steps of Example 4; other steps and conditions are the same as Example 5.

[0075] Comparative Example 1 (Solar Cell)

[0076] The only difference from Example 5 is that no AgSCN is added to the Cs2AgBiBr6 absorption layer film, and the other steps and conditions are the same as those in Example 1; the Cs2AgBiBr6 film prepared is as follows Figure 1 (a) and Figure 2 (a) shown.

[0077] Comparative Example 2 (Cs2AgBiBr6 thin film)

[0078] The only difference from Example 6 is that in the Cs2AgBiBr6 absorption layer film, the Cs2AgBiBr6 crystal preparation step is removed, and instead equal amounts of CsBr, BiBr3, AgBr, and AgSCN (8 mmol CsBr, 4 mmol BiBr3, 4 mmol AgBr, 0.24 mmol AgSCN) are directly dissolved in DMSO and stirred for 2 h to prepare a 0.5 mmol / mL Cs2AgBiBr6 precursor solution. The other steps and conditions are the same as those in Example 6.

[0079] Comparative Example 3

[0080] The only difference from Example 6 is that in the Cs2AgBiBr6 absorption layer film, only AgSCN is changed to NH4SCN, and the other steps and conditions are the same as those in Example 6.

[0081] Performance Testing

[0082] Figure 1 The scanning electron microscope morphology comparison diagram of the Cs2AgBiBr6 film prepared in Comparative Example 1 and the Cs2AgBiBr6 films prepared in Examples 1-4 under different addition amounts of AgSCN, Figure 2 Figure 2 shows the particle size distribution of the Cs2AgBiBr6 film. As can be seen, with increasing AgSCN addition, the surface and morphology of the Cs2AgBiBr6 film undergo significant changes, with the grain size initially increasing and then decreasing. When no AgSCN is added, the grain size is concentrated around 300 nm; when the AgSCN addition is 0.12 mmol, the grain size is concentrated around 600 nm. In particular, when the AgSCN addition is 0.24 mmol, the Cs2AgBiBr6 film reaches its largest particle size, with the grain size concentrated around 1000 nm. When the AgSCN addition is 0.36 mmol, the grain size is concentrated around 600 nm; and when the AgSCN addition is 0.48 mmol, the grain size is concentrated around 500 nm. In particular, when the AgSCN addition amount is 0.24 mmol, the grain size is the largest, the grain boundaries of the film are reduced, and the grain boundary defects are passivated, which helps to suppress the recombination loss of carriers at the grain boundaries and improve the photovoltaic performance of the cell.

[0083] Figure 4 The current-voltage curves of the solar cell devices obtained in Comparative Example 1 and Examples 5-8 are compared. It can be seen from the figure that in Example 6, the amount of AgSCN added (0.24 mmol) is 6% of the molar amount of AgBr, and its short-circuit current density (Jsc, 4.32 mA cm –2), fill factor (FF, 57.68%), and photoelectric conversion efficiency (PCE, 2.95%) were significantly higher than those under other conditions. The PCE of Example 6 was 1.82% higher than that of Comparative Example 1, which confirms the conclusion that it is beneficial to improve the photovoltaic performance of the cell.

[0084] Figure 5 The box-type statistical diagrams of the photovoltaic parameters of the solar cell devices prepared with Cs2AgBiBr6 thin films prepared under different addition amounts of AgSCN in Comparative Example 1 and Examples 5-8 as the light absorption layer. The statistical results show the device V oc (open circuit voltage), FF (fill factor), J The distribution of sc (short-circuit current density) and PCE (photovoltaic conversion efficiency) is shown in Table 1 below.

[0085] Table 1 Comparison of parameters of Cs2AgBiBr6 solar cells obtained in Examples 5-8 and Comparative Example 1

[0086]

[0087] As can be seen from Table 1, the Cs2AgBiBr6 solar cells prepared under different AgSCN addition conditions obtained in Examples 5-8 of the present invention are better than those in Comparative Example 1. J sc (short-circuit current density), V OC (open circuit voltage) and FF (fill factor) have been improved to varying degrees, among which the short circuit current density J sc is 2.94~4.32mA·cm –2 , open circuit voltage V The oc range is 1.12~1.20 V, and the fill factor FF ranges from 50.00 to 57.68%. The photoelectric conversion efficiency of the Cs2AgBiBr6 thin film solar cell prepared under the condition of 0.24 mmol addition is increased from 1.13% (1.08 V, 2.49 mA / cm 2 and 41.69%) to 2.95% (1.18 V, 4.32 mA / cm 2 and 57.68%), which is mainly attributed to J sc In addition, the photovoltaic performance of the solar cell made from the Cs2AgBiBr6 thin film of Example 2 is also better than that of Comparative Example 2 directly using the solution spin coating method and Comparative Example 3 using NH4SCN instead of AgSCN.

[0088] At the same time, in Examples 5-8, V There is basically no significant change in oc and FF: This shows that the addition of AgSCN has a significant effect on the battery Voc and FF have little effect. With the increase of AgSCN addition, J The sc and PCE show a trend of increasing first and then decreasing, which is consistent with the change in the particle size of the Cs2AgBiBr6 film. When the addition amount of AgSCN is 6%, the particle size of Cs2AgBiBr6 reaches the maximum, and the battery J Both sc and PCE are optimal values. This result shows that within the appropriate range, by increasing the particle size, reducing the grain boundaries and maintaining the crystal density, it is possible to effectively improve carrier separation and transport, suppress carrier recombination, and ultimately improve the battery PCE to 1.74-2.95%.

[0089] In summary, the present invention proposes a Cs2AgBiBr6 thin film with controllable particle size, a preparation method, and a solar cell; the steps are as follows: (1) a certain amount of cesium bromide, silver bromide, bismuth tribromide, and hydrobromic acid aqueous solution are placed in a polytetrafluoroethylene reactor liner and stirred until all the solids are dissolved. (2) the liner in step (1) is placed in a reactor, reacted in an oven, and then naturally cooled to room temperature to obtain red and stable Cs2AgBiBr6 crystals. (3) the Cs2AgBiBr6 crystals prepared in step (2) are dissolved in DMSO and stirred to obtain a clear, transparent, and stable yellow Cs2AgBiBr6 precursor solution. (4) the Cs2AgBiBr6 precursor solution prepared in step (3) is deposited on an FTO glass substrate by spin coating to obtain a Cs2AgBiBr6 thin film with good crystallinity. The present invention uses a chemical modification method to optimize the amount of additives to obtain a Cs2AgBiBr6 film with large and controllable particle size, good crystallinity, and dense and uniformity, and assembles the FTO / c-TiO2 / m-TiO2 / Cs2AgBiBr6 / C solar cell device (such as Figure 3 The AgSCN addition (as shown) promotes carrier transport and separation, lowers the carrier transport barrier, and significantly improves the photoelectric conversion efficiency of the resulting Cs2AgBiBr6 solar cell. Specifically, when the AgSCN addition is 6%, the corresponding Cs2AgBiBr6 film has the largest and most uniform particle size, with significantly fewer grain boundaries and grain boundary defects, significantly improving the device's PCE.

[0090] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A solar cell, characterized in that: The invention comprises an FTO glass conductive substrate, a TiO2 electron transport layer, an absorption layer and a carbon top electrode which are stacked in sequence; the absorption layer adopts a Cs2AgBiBr6 thin film, and the raw materials of the Cs2AgBiBr6 thin film include CsBr, AgBr, BiBr3 and AgSCN; Among them, the molar ratio of CsBr, AgBr, and BiBr3 is 2:1:1; The molar ratio of AgBr and AgSCN is 100:(3-9); In the Cs2AgBiBr6 film, the grain size is between 600nm and 1000nm; The method for preparing the Cs2AgBiBr6 thin film comprises the following steps: (1) adding CsBr, AgBr, BiBr3 and AgSCN to the first solvent and stirring until all the solids are dissolved to obtain a mixed solution; (2) The mixed solution undergoes a hydrothermal reaction to obtain Cs2AgBiBr6 crystals; (3) dissolving the Cs2AgBiBr6 crystals in a second solvent to obtain a Cs2AgBiBr6 precursor solution; (4) coating the Cs2AgBiBr6 precursor solution onto a substrate, performing thermal annealing treatment under an inert gas atmosphere, and naturally cooling to room temperature to obtain a Cs2AgBiBr6 thin film with controllable particle size; In step (2), the hydrothermal reaction is carried out at 130°C to 200°C for 2 to 4 hours; In step (4), the thermal annealing treatment is performed at 200°C to 300°C for 5 to 10 minutes; The thickness of the TiO2 electron transport layer is 60-100 nm; the thickness of the absorption layer is 300-350 nm; the thickness of the carbon top electrode is 1.5 μm-1.8 μm; The first solvent is an HBr aqueous solution with a mass concentration of 46-50%; The second solvent is dimethyl sulfoxide.

2. The solar cell according to claim 1, wherein In the mixed solution of step (1), the molar concentration of CsBr is 0.03 to 1.2 mol / L; The stirring until all the solids are dissolved is carried out at 75-85°C.

3. The solar cell according to claim 1, wherein In step (3), the concentration of the Cs2AgBiBr6 precursor solution is 0.46-0.54 mmol / mL.

4. The solar cell according to claim 1, wherein In step (4), the Cs2AgBiBr6 precursor solution is deposited on the substrate by spin coating, the rotation speed during spin coating is 500 to 3000 rpm, and the spin coating time is 35 to 60 s.

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