Open-Circuit Voltage Loss And Humidity Stability In All-Inorganic Perovskite Solar Cells

Lead halide perovskite materials have been widely using in semiconductor devices due to their excellent optoelectronic properties such as tunable band gap,low exciton binding energy,and high charge mobility.In the last decade,power conversion efficiency of perovskite solar cells has been skyrocketing from 3.8%to 25.5%.However,organic-inorganic hybrid perovskites are suffering poor thermal stability due to the presence of organic components,which is harmful for the practical application of perovskite solar cells.All-inorganic perovskites have shown quite superior thermal stability.However,open circuit voltage loss large than 0.6 V in all-inorganic perovskite solar cells extremely limits their ultimate efficiency.In addition,some of them are suffering poor phase stability when exposed in air.Regarding to these issues,in this paper we focused on seeking to mitigate the high open-circuit voltage loss of CsPbI₂Br solar cells.We further explored the CsPbBr₃ film formation and related device humidity stability.(1)By introducing a bilayer electron transport layer ZnO/Mg_xZn_1-xO and a hole transport layer PM6 with deep HOMO level,we obtained high-performance CsPbI₂Br solar cells with an open-circuit voltage loss of 0.58 V.Compared with typical charge transport materials,e.g.,ZnO and spiro-OMETAD,the novel introduced charge transport materials are energetically more compatible with the energy band of CsPbI₂Br,which facilitate the photogenerated electron and hole transfer at perovskite/charge transport layer interfaces.Moreover,the quality of the CsPbI₂Br perovskite film deposited atop bilayer ETL ZnO/Mg_xZn_1-xO is substantially enhanced compared to that on top of ZnO.Both the more favorable energy level alignment and reduced defect density alleviate energy loss in the resultant solar cells.As a consequence,CsPbI₂Br solar cells delivered a champion efficiency of 16%with an open-circuit voltage of 1.34V(open-circuit voltage loss is thus only 0.58 V).Moreover,the absence of the hygroscopic additives for the hole transport layer PM6 greatly enhanced the stability of the device.(2)Concerning the humidity instability of CsPbI₂Br solar cells,we subsequently conducted research on more stable all-inorganic perovskite CsPbBr₃.The CsPbBr₃thin films were fabricated with two-step sequential deposition.CsBr was spin-coated onto the PbBr₂ pre-deposited film,followed by being annealed to allow PbBr₂ and CsBr to react to form CsPbBr₃ inorganic perovskite.This process was repeated several times because of the low solubility of CsBr in methanol.To investigate the effect of electron transport materials on solar cell performance,we compared the quality of CsPbBr₃ films grown onto ZnO and SnO₂.We found that the CsPbBr₃ film deposited on SnO₂ has larger grain size,better crystalline quality,fewer defects.As a result,the device performance using SnO₂ as the electron transport layer is higher.Subsequently,we explored the humidity stability of CsPbBr₃ inorganic perovskite.We found that the humidity stability of CsPbBr₃ inorganic perovskite is better than CsPbI₂Br and FAPbI₃.In this thesis,material synthesis,device construction,and stability have been detailed studied and made some progress.Our work would provide some theoretical and experimental contribution in material and device aspects for all-inorganic perovskite solar cells.