Over 19.2% Efficiency of Organic Solar Cells Enabled by Precisely Tuning the Charge Transfer State Via Donor Alloy Strategy

The large energy loss (Eloss ) is one of the main obstacles to further improve the photovoltaic performance of organic solar cells (OSCs), which is closely related to the charge transfer (CT) state. Herein, ternary donor alloy strategy is used to precisely tune the energy of CT state (ECT ) and thus the Eloss for boosting the efficiency of OSCs. The elevated ECT in the ternary OSCs reduce the energy loss for charge generation (ΔECT ), and promote the hybridization between localized excitation state and CT state to reduce the nonradiative energy loss (ΔEnonrad ). Together with the optimal morphology, the ternary OSCs afford an impressive power conversion efficiency of 19.22% with a significantly improved open-circuit voltage (Voc ) of 0.910 V without sacrificing short-cicuit density (Jsc ) and fill factor (FF) in comparison to the binary ones. This contribution reveals that precisely tuning the ECT via donor alloy strategy is an efficient way to minimize Eloss and improve the photovoltaic performance of OSCs.