Research On Film Forming Process And Surface Engineering Of Inverted Perovskite Solar Cells

Perovskite materials have become a hot spot for research in the field of photovoltaics because of their high absorption coefficient,high carrier mobility,adjustable band gap,and many other advantages,compared with other semiconductor materials.Its power conversion efficiency（PCE）has exceeded 25.75%.However,there are still many problems hindering the further development of perovskite solar cells.Due to the difficulty in controlling the perovskite crystallization process and the interface between the perovskite layer and other functional layers,there are a large number of defects in the perovskite crystal and at interface,on which the photogenerated carriers will be recombined,greatly affecting the PCE.In addition,the presence of defects also leads to the occurrence of current back hysteresis phenomenon.Therefore,improving the crystalline quality of perovskite and the interfacial contact are the primary issues to increase the efficiency of perovskite solar cells.In this study,commonly used 3D inverted（p-i-n type）perovskite solar cells containing FA_0.83Cs_0.17Pb I_2.7Br_0.3 were used as benchmark devices.In order to improve the crystallization of perovskite and reduce defects,bromocresol violet sodium salt（BCP）was added to chlorobenzene（CB）as an additive of perovskite anti-solvent for the first time,benefiting from the strong effect of BCP on perovskite ions.The complexation reduces the density of defect states of the perovskite crystal and improves the fill factor（FF）and PCE of the perovskite solar cell.It was found that the PCE of the devices prepared with anti-solvent containing 0.4 mg/m L of BCP increased from 10%to 12.98%,and this result was verified in devices prepared from same perovskite grown on Al₂O₃ interfacial layer,making the PCE of Al₂O₃ layer contained device increased to 16.03%,further confirming the positive effect of BCP on perovskite crystallization.To improve the interfacial contact between perovskite and hole transport layer（HTL）and suppress carrier recombination,an alkali metal halide interfacial layer was inserted between perovskite and HTL to passivate the interface defects.The evaporation deposition process is used to prepare two alkali metal halide interface layer materials,lithium fluoride（Li F）and sodium chloride（Na Cl）.Li F is usually used as the barrier layer between the HTL and the metal electrode in the n-i-p perovskite solar cell.In this disseration,Li F is evaporated as the interface layer between the HTL and the perovskite layer of the perovskite solar cell to improve the wettability of the perovskite on the HTL.The resulted crystal quality of the perovskite has been improved,and the solar cell’s PCE is increase to 15.37%.Compared with the traditional solution method,the Na Cl interface layer prepared by the evaporation process has advantages in film thickness control and coverage,the PCE of the solar cell device with the evaporated Na Cl interface layer increased from13.56%to 14.84%compared with the samples prepared by the traditional solution method.