Controlling Morphology and Voltage Loss with Ternary Strategy Triggers Efficient All-Small-Molecule Organic Solar Cells

Herein, an emerging acceptor L8-BO as the third component was combined with the B1:BO-4Cl system for constructing efficient ternary all-small-molecule organic solar cells (ASM-OSCs). Theoretical, morphological, and crystallographic studies reveal that L8-BO and BO-4Cl possess good compatibility, resulting in alloy-like state formation of two acceptors in ternary blends. The synergistic effect of two acceptors is conducive to forming favorable phase separation and molecular stacking for promoting charge splitting and extraction, which contributes to simultaneously boosting short-circuit current density and fill factor. Furthermore, the alloy-like state of two acceptors and the higher lowest unoccupied molecular orbital energy level of L8-BO assist ternary ASM-OSCs in achieving lower voltage loss with respect to the binary devices. The optimal ternary ASM-OSCs with 20 wt % L8-BO deliver a top-level efficiency of 17.10%. This work demonstrates that not only the morphology but also the voltage loss of the small molecular matrix can be well-manipulated by employing the ternary strategy.