Investigation On The Formation Mechanism Of CsPbBr₃ And Interface Engineering Of Perovskite Solar Cells

Inorganic perovskite materials（CsPbX₃,X=Cl,Br,I）are often used in perovskite solar cells due to their excellent thermal stability.CsPbBr₃ inorganic perovskite material has a band gap of 2.3 e V.The wide band gap and high conduction band make the solar cells have a high open-circuit voltage,and it is the inorganic perovskite absorbent material with the best phase stability.However,it’s easy to produce a variety of mesophases during the preparation process,and the film forming mechanism of inorganic perovskite is not clear,so it is difficult to prepare high purity products.At the same time,due to its narrow light absorption range（350-550 nm）,the ability to generate photoelectrons is relatively weak,and the current density of the device is small,which limits the further improvement of its power conversion efficiency.CsPbBr₃perovskite can not only be used as a light absorbing layer of solar cells,but also as a modification substance of bulk phase and interface to adjust the interface energy level and bulk phase defects and increase the photoelectric performance of solar cell.In view of the above problems,this research focus on CsPbBr₃perovskite solar cells,including two parts:（1）the formation mechanism of CsPbBr₃ inorganic perovskite film under multi-step spin-coating method is studied.The performance of the film is optimized by prolongating the reaction time of Cs Br and Pb Br₂ precursors,and the photoelectric performance of the cell is improved.（2）The mechanism and regulation measures of the interface and bulk phase modification of CsPbBr₃ quantum dots（QDs）on organic-inorganic hybrid perovskite（MAPb I₃）are studied.The modification position and concentration of CsPbBr₃ QDs in MAPb I₃ perovskite solar cells are explored and the effects of CsPbBr₃ QDs on the properties of MAPb I₃ perovskite film and solar cell are investigated.The main conclusions are as follows:1.The multi-step spin coating method is adopted to explore the phase transformation process and film formation mechanism of CsPbBr₃film by changing the spin coating times.It’s found that the phase composition of CsPbBr₃ film is changed in the following order with the increase of spin coating times:Pb Br₂→Cs Pb₂Br₅→CsPbBr₃→Cs₄Pb Br₆.The film preformed in the repeated spin-coating-annealing process hinders the full reaction of subsequent Cs Br with Pb Br₂ and Cs Pb₂Br₅,resulting in the presence of Cs Pb₂Br₅,CsPbBr₃ and Cs₄Pb Br₆.By prolonging the reaction time between Cs Br solution and the precursor film,the reaction can be fully carried out.The Cs Pb₂Br₅ phase reduced and the morphology and grain size of the film can be effectively improved.Under the condition of spin-coating 4 times and 30 seconds reaction time,the open-circuit voltage of CsPbBr₃ inorganic perovskite solar cell is increased from 1.01 V to 1.28 V,and the power conversion efficiency is increased from 5.32%to 6.30%.2.CsPbBr₃ QDs are used as interface and bulk phase modification substances of organic-inorganic hybrid perovskite MAPb I₃,and the effects of CsPbBr₃ QDs on MAPb I₃ perovskite solar cells at different modification positions are explored.The results show that compared with MAPb I₃ film without CsPbBr₃ QDs modification,QDs modification at different positions does not cause changes in phase and crystal structure of MAPb I₃ perovskite.Part of QDs exchange with MAPb I₃ perovskite,leading to the formation of trace Cs_yMA_1-yPb I_3-xBr_x and the change of perovskite band gap.At the same time,QDs act as a heterogeneous nucleation center to reduce the free energy barrier of perovskite film nucleation and make the perovskite film crystallization more uniform and compact.When QDs is mixed into mesoporous Ti O₂ solution,the perovskite film has better crystallization,surface morphology and light absorption performance.The photoelectric conversion efficiency of modified perovskite solar cells increase from 16.66%to 18.10%.In addition,solar cell stability is improved,it can maintain 80%initial efficiency for 20 days in an air atmosphere with ambient humidity below40%.3.CsPbBr₃ QDs are used as bulk phase modification material of organic-inorganic hybrid perovskite MAPb I₃.The influence of CsPbBr₃QDs concentration added into mesoporous Ti O₂ solution on the performance of MAPb I₃ perovskite film and solar cell are investigated.The results show that when the concentration of QDs is increased to 25mg/m L,the crystallization of perovskite film is better,and the absorption value of visible light absorption and carrier separation effect are further improved.Comparing with the film without bulk phase modification,the defect density of the film after modification is reduced,and the photoelectric conversion efficiency is improved to 18.61%.