Ternary polymer solar cells with alloyed non-fullerene acceptor exhibiting 12.99% efficiency and 76.03% fill factor

Highlights: • The PCE is increased from 12.01% to 12.99% by blending 20 wt% FTTCN in acceptors. • The PCE improvement originates from the simultaneously increased J_SC, V_OC and FF. • Two acceptors prefer to form alloyed state, leading to the increased V_OC of ternary PSCs. • Efficient ternary PSCs can be achieved by recombining the advantages of binary PSCs. -- Abstract: Ternary polymer solar cells (PSCs) were purposely designed according to the key photovoltaic parameters of PBDB-T-2F based binary PSCs with FTTCN or IT-2F as acceptor. Although power conversion efficiency (PCE) of FTTCN based binary PSCs is 10.52% and lower than 12.01% of IT-2F based binary PSCs, the relatively large open circuit voltage (V_OC) of 1.01 V is achieved compared with 0.920 V of IT-2F based binary PSCs. The PCE of the optimized ternary PSCs arrives to 12.99% with 20 wt% FTTCN in acceptors, resulting from the simultaneously increased short-circuit current density (J_SC) of 18.18 mA/cm², V_OC of 0.940 V and fill factor (FF) of 76.03% in comparison to IT-2F based binary PSCs. Ternary PSCs exhibit the monotonously increased V_OCs and over 70% FFs along with FTTCN content increase, indicating that FTTCN and IT-2F alloyed acceptor may be formed due to their good compatibility. The morphology of ternary active layers can be well optimized by adjusting FTTCN content, and three photovoltaic parameters can be well balanced for achieving 12.99% PCE. Over 8% PCE improvement can be achieved by employing ternary strategy. This work indicates that alloyed non-fullerene acceptor should have great potential to achieve efficient ternary PSCs with simultaneously increased three photovoltaic parameters.