Optimizing Molecular Crystallinity and Suppressing Electron-Phonon Coupling in Completely Non-Fused Ring Electron...

High open-circuit voltage (V_oc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non-fused ring electron acceptors (NFREAs), HF-BTA33 and HCl-BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron-phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF-BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a V_oc of 1.232 V, higher than that of symmetric analogue F-BTA33 (PCE=10.02 %, V_oc=1.197 V). Notably, PTQ10 : HCl-BTA33 achieves the highest PCE of 12.54 % with a V_oc of 1.201 V due to the long-range ordered π-π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and V_oc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs.