Refined Shockley-Queisser Framework-Guided Acceptor Design Enables Loss-Aware Bandgap Targeting in Organic Solar Cells.

Precise bandgap tuning is critical for maximizing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Here, we refined the Shockley-Queisser model by incorporating sub-bandgap absorption and nonradiative losses, predicting an optimal optical bandgap (Eg) of ∼1.41 eV for Y-series acceptor-based OSCs, higher than the ideal SQ value of 1.34 eV. Guided by this loss-aware target, we designed and synthesized a new acceptor (YCF3-BO) with CF3-terminated core- and branched outer-side chains to achieve the target Eg in PM6:YCF3-BO devices. The resulting binary and ternary devices achieved PCEs of 19.8% and 20.2%, respectively. This performance arises from two synergistic effects: tuning Eg into the refined optimum window enhances photoluminescence quantum yield and suppresses nonradiative recombination, while branched side chains promote a 3D charge-transport network. Furthermore, PM6:YCF3-BO-based photocathodes operated efficiently in underwater solar hydrogen production. This study establishes a unified framework integrating loss-aware bandgap theory with acceptor design and solid-state packing control for advancing organic photovoltaics.