Zwitterion Reduces Open‐Circuit Voltage Loss in Wide‐Bandgap Perovskite Solar Cells with 22% Efficiency and Its Application in Tandem Devices

Wide‐bandgap (WBG) perovskite solar cells (PSCs) can be combined with other narrow‐bandgap cells to form tandem solar cells (TSCs), which have excellent commercialization prospects. However, the component of WBG perovskite is complex, and the crystallization process is difficult to control. Various bulk and surface defects in polycrystalline films lead to severe nonradiative recombination of photogenerated carriers, resulting in severe open‐circuit voltage ( V OC ) loss in WBG PSCs. Herein, a zwitterionic additive is introduced to alleviate the V OC deficit. The sulfinyl group (–SO) in formamidine sulfinic acid (FSA) has a robust interaction with Pb 2+ , which retards the crystallization and improves the crystal quality in perovskite films. Furthermore, FSA has negatively charged centers (–SO 2 − ) and positively charged centers (–C(NH 2 ) 2 + ), which can passivate the halogen and cation vacancies, respectively. The improved crystalline quality and passivated defects reduce the capture of carriers by defects and facilitate higher V OC . With this strategy, the 1.68 eV bandgap PSCs achieve a champion efficiency of 22.06% and a high V OC of 1.25 V ( V OC loss = 0.43 V). Moreover, the 2‐terminal perovskite/silicon TSCs are fabricated with an extraordinary power conversion efficiency of 28.81%.