Efficient Ternary Polymer Solar Cells with Two Well-Compatible Donors and One Ultranarrow Bandgap Nonfullerene Acceptor

Nonfullerene polymer solar cells (PSCs) are fabricated by using one wide bandgap donor PBDB-T and one ultranarrow bandgap acceptor IEICO-4F as the active layers. One medium bandgap donor PTB7-Th is selected as the third component due to the similar highest occupied molecular orbital level compared to that of PBDB-T and their complementary absorption spectra. The champion power conversion efficiency (PCE) of PSCs is increased from 10.25% to 11.62% via incorporating 20 wt% PTB7-Th in donors, with enhanced short-circuit current (J_SC) of 24.14 mA cm⁻² and fill factor (FF) of 65.03%. The 11.62% PCE should be the highest value for ternary nonfullerene PSCs. The main contribution of PTB7-Th can be summarized as the improved photon harvesting and enhanced exciton utilization of PBDB-T due to the efficient energy transfer from PBDB-T to PTB7-Th. Meanwhile, PTB7-Th can also act as a regulator to adjust PBDB-T molecular arrangement for optimizing charge transport, resulting in the enhanced FF of ternary PSCs. This experimental result may provide new insight for developing high-performance ternary nonfullerene PSCs by selecting two well-compatible donors with different bandgap and one ultranarrow bandgap acceptor.