Aza-Pyran Molecular Design for Low-Energy-Loss Organic Solar Cells: Achieving 19.86% Efficiency via Energetic Disorder Regulation
Achieving low-energy-loss organic solar cells requires precise regulation of energetic disorder and intermolecular packing, which remains challenging at the molecular design level. Here, we report an aza-pyran-type molecular design strategy that integrates a sp3-hybridized nitrogen-centered core with a pyran structural motif to regulate aggregation behavior and energetic disorder in non-fullerene acceptors. Two representative acceptors, D10 and D11, are developed, both exhibiting broadened absorption and high open-circuit voltages, while D10 shows more balanced aggregation and improved long-range molecular ordering. When incorporated as guest acceptors into the PM6:L8-BO system, the optimized ternary device achieves a power conversion efficiency of 19.86% with a high VOC of 0.89 V. Detailed optoelectronic analyses reveal reduced non-radiative energy loss (ΔE3 ≈ 0.23 eV), enhanced electroluminescence quantum efficiency (~1.17 × 10-4), and lowered energetic disorder (EU = 25 meV) in the ternary blends. GIWAXS and charge-transport studies further demonstrate that the introduction of D10 promotes enlarged crystalline domains and more ordered π-π stacking, facilitating balanced carrier transport and suppressed recombination. This work establishes an effective molecular design paradigm that links aza-pyran molecular engineering with energy-loss management, providing new insights into the development of high-efficiency, low-energy-loss organic solar cells.