Halogenated thiophene substitutions on quinoxaline unit to achieve morphology optimization in efficient organic solar cells

Halogenated thiophenes are generally used units for constructing organic semiconductor materials for photovoltaic applications. Here, we introduced thiophene, 2-bromothiophene, and 2-chlorothiophene units to the central core of quinoxaline-based acceptors and obtained three acceptors, Qx-H, Qx-Br, and Qx-Cl, respectively. Compared with Qx-H, Qx-Br and Qx-Cl showed enhanced absorption, down-shifted energy levels, improved crystallinity, and reduced energy disorder. The improved crystallinity significantly optimized the blend morphology, leading to efficient charge generation and transport and, therefore, less bimolecular recombination. Eventually, PM6:Qx-Br-based devices exhibited an outstanding power conversion efficiency of 17.42% with a high open-circuit voltage (V_OC) of 0.915 V. Furthermore, Y6 was introduced into the PM6:Qx-Br binary system to improve the light utilization, and the resulting ternary devices delivered a high PCE of 18.36%. This study demonstrated the great potential of halogenated thiophene substitution in quinoxaline-based acceptors for building high-performance organic solar cell acceptor materials.