Optimization Of Light Absorption Layer For CsPbI₃ All-inorganic Perovskite Solar Cells Prepared By Low Temperature Solution Method

In recent years,perovskite materials have been widely used in the research of solar cells due to its excellent photoelectric performance.The cell efficiency has broken through from the initial 3.8%to the current 25.7%in just over ten years.CsPbI₃solar cells have become one of the researching focuses due to their excellent thermal stability and suitable optical band gap（1.7 e V）and the highest efficiency has broken through to21.15%.However,in practical applications,Because of the sensitivity of the base to temperature,requires the preparation of cell devices in low temperature（below 200°C）,the study of low temperature solution method to prepare efficient CsPbI₃solar cells has laid a good foundation for expanding the application field of CsPbI₃perovskite.The photovoltaic performance of perovskite solar cells is closely related to the quality of perovskite thin films.In this paper,the absorption layer of CsPbI₃was prepared by low temperature solution method,and ammonium fluoroborate（NH₄BF₄）and pentafluoropropanamide（PFPA）were used as additives to optimize the CsPbI₃perovskite,so as to prepare highly efficient and stable inorganic CsPbI₃solar cells.At the same time,N-methylpyrrolidone lead iodide（NMPPb I₃）was used to optimize the preparation process of CsPbI₃thin films in order to obtain the battery device with lower preparation temperature requirements.The specific content of the paper is as follows:（1）The low temperature solution method usually uses Sn O₂as the electron transport layer,but the conduction band difference between Sn O₂and CsPbI₃is larger,which limits the photoelectric performance of CsPbI₃cell devices.Ammonium fluoborate（NH₄BF₄）additive was introduced into the solution of CsPbI₃perovskite precursor to solve the problem of energy level mismatch between perovskite layer and electron transport layer.The experimental results show that the introduction of NH₄BF₄can enrich some BF₄^-on the surface of Sn O₂,improve the conduction band value of Sn O₂and reduce the surface work function,so as to improve the energy level matching at the interface.At the same time,NH₄⁺can interact with the Pb-I octahedron in the solution of CsPbI₃precursor,inhibit the aggregation of Pb-I octahedron,reduce the number of nucleation sites,and thus promote the grain growth of perovskite films.The resulting CsPbI₃perovskite solar cell has an open-circuit voltage of 1.13V and a photoelectric conversion efficiency of 15.15%.（2）Pentafluoropropionamide（PFPA）was introduced into CsPbI₃precursor solution as an additive to solve the problems of more defects and poor stability of CsPbI₃film.The results show that the carbonyl group（C=O）in PFPA molecules is complexed with the lead ion(Pb²⁺)in the solution of CsPbI₃precursor,thus delaying the crystallization process of CsPbI₃films and passivating the uncoordinated Pb²⁺defects in perovskite films.At the same time,amino（-NH₂）in PFPA molecules can interact with iodide（I^-）in perovskite,passivating uncoordinated I-defects,and finally obtain high quality CsPbI₃films with larger grain size and fewer defects.In addition,the carbon-fluorine bond（C-F）in PFPA can form a good hydrophobic layer on the surface of perovskite thin film,improving the stability of CsPbI₃battery devices.The optimized CsPbI₃cell has a photoelectric conversion efficiency of 15.30%and good stability.（3）Using N-methylpyrrolidone lead iodide（NMPPb I₃）to reduce the annealing temperature of CsPbI₃to meet the low temperature requirements of flexible substrate polyester（PET）.The experimental results show that the annealing temperature of CsPbI₃perovskite thin films can be significantly reduced by mixing NMP,Pb I₂and HI to prepare NMPPb I₃instead of the existing dimethyl lead iodide（DMAPb I₃）to prepare precursor solution.For the first time,non-DMAPb I₃mesophase was used to prepare CsPbI₃perovskite thin film,and the black phase CsPbI₃thin film was successfully obtained under the condition of low temperature annealing（140°C）,which further reduced the annealing temperature.At the same time,the CsPbI₃solar cell device prepared with PFPA additive obtained 9.29%photoelectric conversion efficiency,showing a good application prospect.