Efficient Ternary Organic Solar Cells with Two Compatible Non‐Fullerene Materials as One Alloyed Acceptor

: Efficient ternary organic solar cells (OSCs) are fabricated by employing a polymer PBT1-C as the donor and two non-fullerene materials, MeIC and MeIC2, as one alloyed acceptor. The optimized ternary OSCs with 30 wt% MeIC2 in acceptors achieve a power conversion efficiency (PCE) of 12.55%, which is much higher than that of 11.47% for MeIC-based binary OSCs and 11.41% for MeIC2-based binary OSCs. The >9.4% improvement in PCE is mainly attributed to the optimized photon harvesting and morphology of ternary active layers, resulting in the simultaneously improved short-circuit current and fill factor. Furthermore, good compatibility and similar lowest unoccupied molecular orbital energy levels of MeIC and MeIC2 are beneficial to form one alloyed acceptor for efficient electron transport in the ternary active layers. This work may provide new insight when selecting the third component for preparing efficient ternary OSCs.