Ternary organic solar cells (OSCs) have been widely demonstrated as an effective method to improve device performance. Here, a series of ternary OSCs is fabricated with a polymer PM6 as donor and well-compatible BTP-eC9 and ITIC-Th as acceptor. The open-circuit voltage (Voc) of ternary OSCs monotonously increases along with ITIC-Th incorporation, indicating that the alloy state should be formed between BTP-eC9 and ITIC-Th. The energy loss can be minimized by incorporating ITIC-Th, leading to the Voc improvement of ternary OSCs. A power conversion efficiency (PCE) of 18.69% is achieved in the optimized PM6:BTP-eC9:ITIC-Th ternary OSCs by incorporating 15 wt% ITIC-Th in the acceptor, resulting from the simultaneously increased short-circuit current density (Jsc) of 28.00 mA cm-2, Voc of 0.868 V, and fill factor (FF) of 76.95%. The Jsc and FF improvement of ternary OSCs are ascribed to comprehensively optimal photon harvesting, exciton dissociation, and charge transport in ternary active layers. Over 8% PCE improvement can be achieved by employing ternary strategy, compared with that of PM6:BTP-eC9- binary OSCs. This work indicates that non-fullerene alloyed acceptor has great potential to achieve efficient ternary OSCs with simultaneously improved photovoltaic parameters.

Ternary organic solar cells with power conversion efficiency >18.6%

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