Efficient Targeted Regulation of the Interfaces and Bulk in Inverted Perovskite Solar Cells With a [closo‐B12H12]2−‐based Derivative

Abstract The performance and stability of inverted perovskite solar cells (PSCs) is adversely affected by the recombination loss, ion migration, and residual stress arising from issues within the bulk and at the cathode interface. Using simple post‐treatment with a novel solution‐processable derivative of the dodecahydro‐ closo ‐dodecaborate anion ([ closo ‐B 12 H 12 ] 2− )—(TBA) 2 [B 12 H 11 (OCH 2 CH 2 ) 2 OH] (TBA 2 B)—it is simultaneously address these issues. In inverted PSCs, the cationic and anionic components of TBA 2 B uniquely self‐separate by positioning themselves precisely to perform their specific modification functions. The majority of [B 12 H 11 (OCH 2 CH 2 ) 2 OH] 2‐ anions reside at the (6,6)‐phenyl‐C 61 butyric acid methyl ester (PCBM)/Ag interface, which enhances the electrical and physical contact. Additionally, a substantial fraction of tetrabutylammonium cations diffuse into the perovskite/PCBM heterojunction, enabling comprehensive control over the trap passivation, stress release, ion migration elimination, and grain boundary reinforcement through the in situ formation of 1D TBAPbI 3 on the surface of the perovskite crystals. The TBA 2 B devices exhibit high power conversion efficiency of 25.59% and open‐circuit voltage of 1.199 V, performance that is among the highest achieved with a solution‐processed perovskite/PCBM heterojunction. Furthermore, TBA 2 B significantly enhances the device's stability. This study provides crucial insights into the design of efficient and solution processable [ closo ‐B 12 H 12 ] 2− ‐based interface materials, and offers a comprehensive understanding of the underlying modification mechanisms.