ITC-2Cl: A Versatile Middle-Bandgap Nonfullerene Acceptor for High-Efficiency Panchromatic Ternary Organic Solar Cells

An effective way to improve the power conversion efficiency of organic solar cells (OSCs) is to use the ternary architecture consisting of a donor, an acceptor, and a third component. Identifying the proper third component for successful ternary OSCs, however, is not an easy task. Herein, it is demonstrated that a middle-bandgap acceptor, ITC-2Cl, functions as a successful third component for several wide-bandgap donor: ultranarrow bandgap acceptor binary systems (PBDB-T-2F: F8IC, PBDB-T-2F: IOIC-2Cl, and PBDB-T-2Cl: IOIC-2Cl). Photovoltaic parameters, including V_OC, J_SC, fill factor (FF), and power conversion efficiency (PCE), are effectively improved by incorporating ITC-2Cl, which lies in the complementary absorption of ITC-2Cl and host binary system, high-lying LUMO level of ITC-2Cl, and the inhibition of bimolecular recombination. The ternary device based on PBDB-T-2Cl: ITC-2Cl: IOIC-2Cl achieves a champion PCE of 14.75% (certified as 13.78%) with a very low energy loss of 0.48 eV. These results provide critical insight into the ternary strategy and encourage re-evaluation and restudy of the photoactive materials previously reported with moderate performance.