Multifunctional Phosphorus‐Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture‐Stable Perovskite Solar Cells

• Published in: Advanced functional materials Vol. 30; no. 15
• Main Authors: Yang, Zhi, Dou, Jinjuan, Kou, Song, Dang, Jialin, Ji, Yongqiang, Yang, Guanjun, Wu, Wu‐Qiang, Kuang, Dai‐Bin, Wang, Minqiang
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.04.2020
• Subjects: Acids; Circuits; Defects; Degradation; Efficiency; Fluorine; Lewis acid; lewis acids; lewis bases; Materials science; Moisture resistance; moisture stable solar cells; multiple‐cation lead mixed‐halide perovskites; Passivity; Perovskites; phase segregation; Phosphorus; Photovoltaic cells; Relative humidity; Solar cells; Stability; Synergistic effect; trap passivation
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201910710

Multiple‐cation lead mixed‐halide perovskites (MLMPs) have been recognized as ideal candidates in perovskite solar cells in terms of high efficiency and stability due to decreased open‐circuit voltage loss and suppressed yellow phase formation. However, they still suffer from an unsatisfactory long‐term moisture stability. In this study, phosphorus‐containing Lewis acid and base molecules are employed to improve device efficiency and stability based on their multifunction including recombination reduction, phase segregation suppression, and moisture resistance. The strong fluorine‐containing Lewis acid treatment can achieve a champion PCE of 22.02%. Unencapsulated and encapsulated devices retain 63% and 80% of the initial efficiency after 14 days of aging under 75% and 85% relative humidity, respectively. The better passivation of Lewis acid implies more halide defects than Pb defects at the MLMP surface. This unbalanced defect type results from phase segregation that is the synergistic effect of Cs and halide ion migrations. Identifying defect type based on different passivation effects is beneficial to not only choose suitable passivators to boost the efficiency and slow down the moisture degradation of MLMP solar cells, but also to understand the mechanism of defect‐assisted moisture degradation. A strong fluorine‐containing Lewis acid tris(pentafluorophenyl) phosphine (TPFP) is developed to passivate mixed perovskite solar cells, achieving a champion efficiency of 22.02% and a high stability under 85% relative humidity. The moisture degradation mechanism is phase segregation of I‐rich black phase and Cs/Br‐rich yellow phase resulting from water‐assisted synergistic Cs and halide ion migrations.