Phenothiazine-Based Solid Additives for Optimizing Film Morphologies in High-Performance Organic Photovoltaics

In this study, we introduce two volatile solid additives based on phenothiazine (PTz) derivatives with different N-substituents: ethyl (PTz-Et) and phenyl (PTz-Ph), into the PM6:Y6 photoactive layer system. The incorporation of PTz-Et and PTz-Ph enhances inter- and intramolecular stacking in neat PM6, neat Y6, and the blended PM6:Y6 films after thermal annealing, as evidenced by changes in absorption profiles. These improvements lead to more efficient exciton dissociation, optimized phase separation, balanced charge carrier transfer and transport, and reduced charge recombination, collectively enhancing the efficiency and stability of organic solar cells (OSCs). PTz-Et-treated PM6:Y6 blend achieves a remarkable enhancement in power conversion efficiency (PCE), increasing from 14.57% to 15.75%, along with improvements in short-circuit current (J_SC) from 25.16 to 26.05 mA/cm² and fill factor (FF) from 70.0% to 74.6%, and better device stability. This study demonstrates the effectiveness of PTz-based volatile solid additives and positions them as promising candidates for OSC commercialization.