Simultaneously optimizing exciton diffusion length and nonradiative energy loss in organic solar cells via ternary strategy

Significant nonradiative energy loss and short exciton diffusion length in organic solar cells (OSCs) are two major obstacles to achieving state-of-the-art efficiencies. It is crucial to conduct a study on the intensive mechanism and improvement strategies for future breakthroughs in the efficiency of OSCs. In this work, nonradiative energy loss and exciton diffusion length are optimized simultaneously by incorporating a guest acceptor (LA15) to construct ternary OSC (D18:L8-BO:LA15). Firstly, LA15 exhibits excellent compatibility with the host acceptor L8-BO, and effectively improves the fluorescence quantum efficiency (FLQY), resulting in suppressed non-radiative energy loss. Moreover, LA15 effectively prolongs the fluorescent lifetime of the acceptor phase from 0.85 to 1.12 ns, leading to larger exciton diffusion length, which is beneficial for reducing geminate recombination. Besides, the addition of LA15 optimizes the crystallinity of the active layer with amplified charge transport capacity. As a result, the optimized D18:L8-BO:LA15 device achieves ultralow nonradiative energy loss of 0.18 eV and improved fill factor (FF) with high efficiency up to 19.13%. These results highlight the crucial roles of regulating FLQY and exciton lifetime in achieving high-efficiency OSCs.