Alloy-like ternary polymer solar cells with over 17.2% efficiency

Ternary strategy has been considered as an efficient method to achieve high performance polymer solar cells (PSCs). A power conversion efficiency (PCE) of 17.22% is achieved in the optimized ternary PSCs with 10 wt% MF1 in acceptors. The over 8% PCE improvement by employing ternary strategy is attributed to the simultaneously increased J_SC of 25.68 mA cm^-2, V_OC of 0.853 V and FF of 78.61% compared with Y6 based binary PSCs. The good compatibility of MF1 and Y6 can be confirmed from Raman mapping, contact angle, cyclic voltammetry and morphology, which is the prerequisite to form alloy-like state. Electron mobility in ternary active layers strongly depends on MF1 content in acceptors due to the different lowest unoccupied molecular orbital (LUMO) levels of Y6 and MF1, which can well explain the wave-like varied FF of ternary PSCs. The third-party certified PCE of 16.8% should be one of the highest values for single bulk heterojunction PSCs. This work provides sufficient references for selecting materials to achieve efficient ternary PSCs.