Facile Strategy for Reducing Cell-to-Module Efficiency Gap in Organic Solar Cells by Controlling the Preaggregation of Photoactive Solutions

Organic solar cells (OSCs) have recently achieved efficiencies of >20% in single-junction unit cells owing to rapid advancements in materials and device technologies. Large-area OSCs face several challenges that adversely affect their efficiency compared to small unit cells. These challenges include increased resistance loads derived from their larger dimensions, as well as limitations related to morphology, miscibility, and crystallinity. In this study, a preaggregation control technique was employed to develop efficient OSC modules. This was achieved by incorporating a low-concentration D18 solution into a high-performance donor–acceptor combination of PM6 and L8-BO facilitating optimal chain entanglement. As a result, macroscopically clean films and microscopically phase-separated morphologies were obtained. For devices with a small area of 0.04 cm2, the device incorporating D18 exhibited a marginally higher power conversion efficiency (PCE) of 17.82% compared to 17.32% for the device without D18. For devices with significantly larger areas of 4.725 and 30.24 cm2, the PCEs increased significantly with the introduction of D18, rising from 14.85 to 15.31% and from 12.77 to 13.49%, respectively. In particular, the module with the largest area of 30.24 cm2 demonstrated a significant decrease in load resistance, leading to a substantial reduction in the cell-to-module efficiency gap, which decreased from 26.3 to 24.3%.