Coumarin‐Based Volatile and Non‐Volatile Solid Additives Enable Organic Solar Cells with 20.32% Efficiency

Abstract

Abstract Solid additives, including volatile solid (VS) and non‐volatile solid (non‐VS) additives, have drawn great attention due to their crucial function in improving photovoltaic performance of organic solar cells (OSCs), while the post‐treatment of non‐VS additives is more convenient. However, compared with VS additives, non‐VS additives often fall‐short in optimizing device morphology, and their systematic comparisons in working mechanisms are still lacking. Herein, we design and synthesize two coumarin‐derived additives, including volatile 7‐(diethylamino)‐2 H ‐chromen‐2‐one (C5) and nonvolatile 3‐(benzo[ d ]thiazol‐2‐yl)‐7‐(diethylamino)‐2 H ‐chromen‐2‐one (C6), to assess their various impacts on device performance. Both the C5‐ and C6‐treated OSCs obtain optimized morphology, improved charge transfer, and less energy loss than the additive‐free device, while C6 plays an additional charge transport channel to promote the exciton utilization through Föster‐Reasonable energy transfer (FRET) between C6 and the donor. As a result, the OSC based on C6 treated D18:L8‐BO obtained an impressive efficiency of 20.32%, as the highest value among the reported small molecule non‐VS additive‐treated devices, which is higher than those of additive‐free (18.85%) and C5‐treated (19.55%) ones. Our work provides a deep insight into the different mechanisms by which non‐VS and VS additives boost photovoltaic performance of the resulting OSCs.