Improved Exciton Diffusion through Modulating Förster Resonance Energy Transfer for Efficient Organic Solar Cells

Förster resonance energy transfer (FRET) is commonly utilized in organic solar cells (OSCs) to enhance the power conversion efficiency (PCE) by promoting molecular interactions. The PCE is greatly affected by the number of photo‐generated excitons that effectively reach interfaces between the donor and acceptor materials of OSCs. However, the correlation between FRET and exciton diffusion has received limited attention. Therefore, it is crucial to understand and manipulate FRET process for investigating exciton dynamics in OSCs. Herein, BTA3 and its derivatives are chosen as the third components and energy donors to elucidate the intrinsic photophysical mechanism of FRET in OSCs by manipulating their efficiency. The results unambiguously demonstrate that the addition of guest F‐BTA3 exhibits the highest FRET efficiency, leading to a significant enhancement in the PCE of both PM6:Y6 and PM6:PY‐IT host systems. By correlating FRET process and exciton dynamics, this enhancement to remarkable increment in exciton diffusion length is attributed. Experimental results and theoretical simulations indicate high FRET efficiency arises from strong dipole–dipole interaction, and exhibits a positive correlation with exciton diffusion length. This study showcases the effective regulation of exciton diffusion in OSCs through modulation of FRET, offering a novel perspective for optimizing the performance of organic photovoltaic devices.