Study On High Stability CsPbI₃ Perovskite Films And Solar Cells Devices

In recent years,the efficiency of all-inorganic CsPbI₃ perovskite solar cells has increased from initial 2.7%to 21%now.Besides the rapid improvement in efficiency of the inorganic solar cells,inorganic CsPbI₃solar cells have become the focus of perovskite solar cell research due to the excellent thermal stability and photostability.Among them,CsPbI₃ has four phase structures including cubic phase（α）,tetragonal phase（β）,orthonormal phase（γ）and monoclinic non-perovskite phase（δ）.Theα,βandγphases belong to the black perovskite phase.Theαβandγphases of inorganic CsPbI₃ have a band gap of ca.1.7 e V.However,the phase stability of black perovskite phase is poor at room temperature.Under high humidity condition,the black CsPbI₃ phase spontaneously transforms into a non-perovskiteδ-CsPbI₃phase with a band gap of 2.3 e V.Recent studies have shown that HPbI₃ synthesized using the reaction of PbI₂ and HI acid in dimethylformamide（DMF）not only reduces the phase transition temperature ofα-CsPbI₃ but also greatly improves its phase stability.For inorganic perovskite materials,there are few reports on the effects of doping alkaline metal iodide into inorganic CsPbI₃ films or preparing two-dimensional inorganic perovskite materials.Based on the preparation of compact CsPbI₃ films without holes and the improvement in stability of perovskite solar cells,the following experimental investigations were made in this thesis:1)The properties of the inorganic CsPbI₃ films prepared under different annealing conditions and the performance of the devices were studied.By using the one-step annealing and muli-step annealing to treat the absorption layer,it is found that the grain size and the morphology of the films prepared by the muli-step annealing are better than those prepared by direct one-step annealing.At the same time,the solar cell devices prepared by muli-step annealing are also higher than those prepared by step annealing.The parameter difference between solar cells is mainly reflected in the change of solar cell filling factor.The cells prepared by muli-step annealing have a filling factor of 38.6,while the cells by one-step annealing have only22.7.2)The properties of the alkaline metal iodide（NaI,KI）doped inorganic CsPbI₃films and the performance of the solar cells devices were studied.By doping the 0%,2.5%,5%,7.5%,10%alkaline metal iodide to the inorganic CsPbI₃ perovskite precursor solution,it is found that the crystallinity of the film doped with trace of NaI is ronghly improved,the phase stability of the film decreased sharply.The crystal quality and grain size of films doped with 5%KI are improved obviously.Correspondingly,the parameters of the solar cells have also been improved obviously.The open circuit voltage of the solar cell without alkali metal iodide doping is 0.854 V,and the maximum open circuit voltage of the cell with alkali metal iodide doping is0.934 V.The corresponding filling factor was also increased from 38.6 to 51.1.However,the phase stability of the films hardly improved after the doping of KI.3)The properties of the CMA₂Cs_n-1Pb_nI_3n+1 films with different n values of cyclohexanmethylamine iodine（CMAI）and the performance of the solar cells devices were studied.Through the study of the two-dimensional perovskite films with n of 6,8,10,15,∞and the solar cell devices,it is found that the phase stability of the two-dimensional films prepared with n of 8 has greatly improved.Under the the20%-humidity condition,the color of the CMA₂Cs₇Pb₈I₂₅ films do not obviously change after 10 days,while the color of the inorganic perovskite films without two-dimensional phase has obviously changes after 3 days.It shows that the formation of two-dimensional phase in CsPbI₃ films is beneficial to improve the stability of the films.