20.34% efficiency organic solar cells with optimal fibrous morphology and low energy loss

In this study, we incorporated Z19, a highly crystalline non-fullerene acceptor (NFA) with high photoluminescence quantum yield (PLQY), into the D18:BTP-eC9-4F system. Z19 effectively modulated the fibrous morphology of the active layer and reduced energy loss to 0.542 eV. Due to its excellent compatibility with BTP-eC9-4F, an alloy-like acceptor phase was formed. With a Z19 ratio of 30%–50%, the power conversion efficiency (PCE) consistently exceeded 20%, showing remarkable insensitivity to composition. At 40% Z19, the device achieved a PCE of 20.34% and a fill factor (FF) of 81.11%. Moreover, the semi-transparent organic solar cells (ST-OSCs) demonstrated light utilization efficiency (LUE) of 5.2%, an average visible transmittance (AVT) of 34.7%, and a PCE of 15%, with stability comparable to opaque devices. These results highlight that incorporating a high-PLQY, highly crystalline third component is an effective strategy for enhancing organic solar cell performance.