Highly efficient all-small-molecule organic solar cells with excellent operational stability and blend-thickness tolerance†

Abstract

Optimizing the nanoscale morphology of the active layer is critical for enhancing photovoltaic performance and operational stability in all-small-molecule organic solar cells (all-SMOSCs). However, controlling domain size and phase separation remains particularly challenging due to the similar chemical structure and miscibility of small-molecule donors (SMDs) and acceptors. To address this, we synthesized and incorporated a new SMD (SD86) into a host system (MPhS-C2:BTP-eC9), which led to the formation of a donor alloy (MPhS-C2:SD86). This approach facilitates the optimization of blend microstructure and carrier dynamics. Consequently, we achieved a record power conversion efficiency of 18.51% (certified value: 18.40%, which is the highest value reported so far), attributed to improved charge management (FF × J_SC) and reduced energy loss in this ternary system. Additionally, the ternary system also exhibited remarkable operational stability and superior film-thickness insensitivity. The introduction of three additional all-small molecule systems based on various acceptors further confirms the universality of this donor-alloy strategy in improving efficiency, stability and processability. Overall, our results highlight the importance of the designed donor alloy strategy for morphology control toward high-performance all-SMOSCs.