Wide Bandgap Polymer Donors Based on Succinimide-Substituted Thiophene for Nonfullerene Organic Solar Cells

The advent of nonfullerene acceptors (NFAs) has greatly improved the photovoltaic performance of organic solar cells (OSCs). However, to compete with other solar cell technologies, there is a pressing need for accelerated research and development of improved NFAs as well as their compatible wide bandgap polymer donors. In this study, a novel electron-withdrawing building block, succinimide-substituted thiophene (TS), is utilized for the first time to synthesize three wide bandgap polymer donors: PBDT-TS-C5, PBDT-TSBT-C12, and PBDTF-TSBT-C16. These polymers exhibit complementary bandgaps for efficient sunlight harvesting and suitable frontier energy levels for exciton dissociation when paired with the extensively studied NFA, Y6. Among these donors, PBDTF-TSBT-C16 demonstrates the highest hole mobility and a relatively low highest occupied molecular orbital (HOMO) energy level, attributed to the incorporation of thiophene spacers and electron-withdrawing fluorine substituents. OSC devices based on the blend of PBDTF-TSBT-C16:Y6 achieve the highest power conversion efficiency of 13.21%, with a short circuit current density (J_sc) of 26.83 mA cm^-2, an open circuit voltage (V_oc) of 0.80 V, and a fill factor of 0.62. Notably, the V_oc × J_sc product reaches 21.46 mW cm^-2, demonstrating the potential of TS as an electron acceptor building block for the development of high-performance wide bandgap polymer donors in OSCs.