High Miscibility Compatible with Ordered Molecular Packing Enables an Excellent Efficiency of 16.2% in All-small-molecule Organic Solar Cells.

In all-small-molecule organic solar cells (ASM-OSCs), a high short circuit current (Jsc ) usually needs a small phase separation, while a high fill factor (FF) is generally realized in a highly ordered packing system. However, small domain and ordered packing always contracted each other in ASM-OSCs, leading to a mutually restricted Jsc and FF. In this study, we propose alleviating the previous dilemma by the strategy of obtaining simultaneous good miscibility and ordered packing through modulating homo- and hetero- molecular interaction. By moving the alkyl-thiolation side chains from para- to meta-position in the small-molecule donor, the surface tension and molecular planarity are synchronously enhanced, resulting in compatible properties of good miscibility with acceptor BTP-eC9 and strong self-assemble ability. As a result, an optimized morphology with multi-length scale domains and highly ordered packing is realized. The device exhibits a long carrier lifetime (39.8 us) and fast charge collection (15.5 ns). A record efficiency of 16.2% with a high FF of 75.6% and a Jsc of 25.4 mA cm-2 in the ASM-OSCs is obtained. These results demonstrate that the strategy of simultaneously obtaining good miscibility with high crystallinity could be an efficient photovoltaic material design principle for high performance ASM-OSCs. This article is protected by copyright. All rights reserved.