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 SnI₂/PbI₂ 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 Sn²⁺ from oxidation. The optimized (HC(NH₂)₂)_n(CH₃NH₃)_1-nPb_0.7Sn_0.3I_xBr_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.