Unraveling abnormal buried interface anion defect passivation mechanisms depending on cation-induced steric hindrance for efficient and stable perovskite solar cells

Although ionic liquids (ILs) have been widely employed to heal the defects in perovskite solar cells (PSCs), the corresponding defect passivation mechanisms are not thoroughly understood up to now. Herein, we first reveal an abnormal buried interface anion defect passivation mechanism depending on cation -induced steric hindrance. The IL molecules containing the same anion (1BF4]-) and different sizes of imi-dazolium cations induced by substituent size are used to manipulate buried interface. It was revealed what passivated interfacial defects is mainly anions instead of cations. Theoretical and experimental results demonstrate that the large-sized cations can weaken the ionic bond strength between anions and cations, and facilitate the interaction between anions and SnO2 as well as perovskites, which is con-ducive to interfacial defect passivation and ameliorating interfacial contact. It can be concluded that interfacial chemical interaction strength and defect passivation effect are positively correlated with the size of cations. The discovery breaks conventional thinking that large-sized modification molecules would weaken their chemical interaction with perovskite. Compared with the control device (21.54%), the device based on 1,3-Bis(1-adamantyl)-imidazolium tetrafluoroborate (BAIMBF4) with maximum size cations achieves a significantly enhanced efficiency of 23.61% along with much increased moisture, ther-mal and light stabilities. (c) 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

By investigating the defect repair mechanism of ionic liquids in perovskite solar cells, it was found that an abnormal buried interface defect passivation mechanism is induced by cation-induced steric hindrance. The results reveal that interfacial defect passivation relies on anions rather than cations. The study also demonstrates that large-sized cations can weaken the ionic bond strength between anions and cations, promoting the interaction between anions and SnO2 and perovskites, leading to improved defect passivation and interfacial contact.