Solvent‐Induced Copper Vacancy in CuSCN Layer: A Strategy to Boost Conductivity and Optimize Energy Levels for Efficient Organic Solar Cells

Abstract Copper(I) thiocyanate (CuSCN) is a prominent wide‐bandgap p‐type semiconductor with desirable transparency and chemical robustness. Whereas intrinsic limitations, such as its relatively low Fermi level ( E F ) and modest electrical conductivity, have impeded its broader application in organic solar cells (OSCs). This study introduces a novel approach to modify the electronic properties of CuSCN by inducing copper vacancies through the use of specific solvent mixtures, thereby enhancing its suitability for OSCs. The effects of two solvent mixtures, methanol/ammonia (CH 3 OH/NH 4 OH) and dimethyl sulfoxide/ N , N ‐Dimethylformamide (DMSO/DMF) is have systematically investigated, on the CuSCN layer. The findings reveal that these solvent systems induce a higher concentration of copper vacancies within the CuSCN film, resulting in a significant reduction of the E F and a substantial increase in electrical conductivity. These modifications have led to the improved energy level alignment with the PM6:L8‐BO:BTP‐eC9 blended photoactive layers, culminating in a marked enhancement of the power‐conversion efficiencies of 19.10% for the DMSO/DMF processed CuSCN layer. Additionally, it has observed enhanced shelf/thermal stability and thickness tolerance of OSCs based on these CuSCN films. This work not only presents a novel strategy for modifying the performance characteristics of CuSCN but also underscores its potential to contribute to the advancement of photovoltaic technologies.