4-Bromobenzylamine Bidirectional Regulation Strategy Enables High-Efficiency and Stable Sn–Pb Perovskite Solar Cells

The poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT/PSS) mixed polymer is characterized by high conductivity and a simple preparation process, making it an excellent hole transport material for inverted Sn–Pb perovskite solar cells (PSCs). However, the acidic substances produced by PEDOT/PSS upon exposure to moisture and quick crystallization of Sn–Pb perovskite films on its surface may decrease device performances. Herein, an effective bidirectional regulation strategy was developed by introducing 4-bromobenzylamine hydrochloride (4-BBAC) molecules into the interface between PEDOT/PSS and the perovskite, inducing efficient and stable inverted Sn–Pb PSCs. The 4-BBAC molecules modified the surface of PEDOT/PSS, improved the conductivity of PEDOT/PSS, and weakened the acidity caused by moisture absorption of PEDOT/PSS, thereby improving the stability of the resulting PSCs. Moreover, the crystallization process of the Sn–Pb perovskite can be controlled since 4-BBAC can react with SnI 2 /PbI 2 to form a two-dimensional phase, which can slow down the crystallization rate of Sn–Pb perovskite films for improved-quality perovskite films and prevent Sn 2+ from oxidation. The optimized (HC(NH 2 ) 2 ) n (CH 3 NH 3 ) 1- n Pb 0.7 Sn 0.3 I x Br 3- x devices exhibited a higher power conversion efficiency (PCE) of 18.36%, superior to that of the control PSCs (16.23%). Besides, the unencapsulated PSCs modified by 4-BBAC maintained 71% of their initial PCE after aging for 300 h under relative humidity conditions of 20 ∼ 30%, while the control PSCs showed almost no photovoltaic conversion efficiency under the same conditions. Overall, a new technical implementation scheme was provided to guide the future fabrication of efficient and stable Sn–Pb PSCs.