Substituted quinoxaline based small-molecule donor guests enable 19% efficiency ternary organic solar cells

Abstract

The rational design of guest small molecule donors for ternary organic solar cells is still a challenge. Herein, we designed and synthesized two novel small-molecule donor third components using ethyl (QxBE) and isopropyl formate (QxBC) substituted quinoxalines as acceptor units. The stronger electron withdrawing ability of the isopropyl formate group and the small torsion angle provide QxBC with obviously red-shifted absorption and tighter molecular packing than QxBE. Both molecules exhibited complementary absorption and good miscibility with the host PM6:L8-BO blend system. The incorporation of these two molecules into the PM6:L8-BO system facilitated a fibrous network structure, enhanced crystallinity and optimized vertical phase distribution. This results in suppressed charge recombination and balanced charge transport ability. Consequently, QxBC-based ternary OSCs exhibited simultaneous enhancements in open-circuit voltage (V_OC) (0.898 V), short-circuit current (J_SC) (26.49 mA cm⁻²), FF (80.04%) and PCE (19.04%), representing record values for ternary OSCs with small-molecule donors as the third component. Furthermore, the storage/thermal stability of ternary OSCs has been significantly improved. These results imply in-depth insights into the structure–property relationship of SMD third components manipulated by the middle bridge unit, and provide new strategies for effective molecular design of SMD third components toward high-performance ternary OSCs.