Optimized Molecular Packing through Selenium‐Substituted Non‐Fullerene Acceptor for Trap Density Reduction in High‐Performance Organic Solar Cells

ABSTRACT High trap density and localized electronic states within the semiconductor bandgap of the photoactive layer are a great challenge for the organic solar cells (OSCs). In this work, we successfully designed and synthesized a selenium substituted small‐molecule acceptor BSP‐F, featuring high crystallinity, which can reduce the trap density by facilitating the formation of more intimate molecular packing. The incorporation of BSP‐F to the binary D18:L8‐BO materials system optimizes the nanoscale morphology of the active layer and enhances molecular order, which can enhance the charge transporting properties, thereby effectively suppressing non‐radiative recombination. Eventually, the D18:L8‐BO:BSP‐F based devices deliver a high efficiency of 20.07% with a significantly decreased trap density of 7.93 × 10 15 cm −3 and a low non‐radiative energy loss of 0.174 eV. This work presents an effective approach for realizing high‐efficiency, low energy loss OSCs by employing morphology control to mitigate disorder.