An efficient enhancement in organic photovoltaics by introducing simple-structured benzo[1,2-b:4,5-b′]dithiophene-based large-bandgap small molecules as the third component

The ternary strategy has been widely demonstrated as an efficient and facile method to improve the performance of organic photovoltaics (OPVs). Besides employing commonly used relatively complex molecules or copolymers, developing cost-effective and simple third components with rational structure design and suitable modification also has great potential to construct ternary system with high power conversion efficiency (PCE), though it is challenging. Herein, we designed and synthesized a series of simple molecules BR-X (BR-RD, BR-OC8, and BR-C8) based on the benzo[1,2-b:4,5-b′]dithiophene core with the modification of side chains and end-groups as the third components to the host binary PM6:Y6 system for promoting the photovoltaic performance. The ternary system with the addition of BR-RD or BR-C8 demonstrated promoted molecular packing, facilitated exciton dissociation, and charge transportation with obvious suppression of carrier recombination. While BR-OC8 showed a limited role in the improvement of the above performance in its ternary blend. Further investigation indicates that BR-RD and BR-C8 are more inclined to mix with PM6 than Y6 and can be beneficial in the formation of larger pure Y6 domains than those with a binary system and reduced mixed-phase. Thus, ternary devices with BR-RD and BR-C8 achieve highest efficiencies of 17.49% and 17.28% with all simultaneously boosted photovoltaic parameters, respectively, while the ternary device with BR-OC8 exhibits less improvement in PCE compared to that of the host binary one (16.73% vs. 16.42%). This work not only provides an affordable strategy to improve the photovoltaic performance but also enriches the material abundance of novel simple third components to achieve highly efficient ternary OPVs.