Antisolvent Treatment on Wet Solution‐Processed CuSCN Hole Transport Layer Enables Efficient and Stable Perovskite Solar Cells

Abstract Among the various inorganic hole‐transporting materials for perovskite solar cells (PSCs), CuSCN is identified as a promising candidate for commercialization applications owing to its abundance and solution processability with alkyl sulfides. Although CuSCN possesses high intrinsic thermal stability, the existence of diethyl sulfide (DES) residue during the wet processing of CuSCN films accelerates perovskite degradation, impeding the practical application of CuSCN in PSC applications. This study demonstrates a new antisolvent‐treatment strategy to extract DES residue from CuSCN. The antisolvent treatment with the aid of diethyl ether (DEE) successfully results in a dense and high‐quality CuSCN film with improved surface morphology, trap density, and hole extraction ability. Consequently, the power conversion efficiency of DEE‐treated CuSCN‐based PSCs improves from 16.84% to 18.34% with superior long‐term stability. This study provides a simple method for the preparation of high‐quality CuSCN films that can effectively be applied to the large‐area fabrication of CuSCN‐based PSCs.