Nonfullerene Polymer Solar Cells Reaching a 9.29% Efficiency Using a BODIPY-Thiophene Backboned Donor Material

A conjugated polymer donor containing BODIPY-thiophene dyads in the backbone, P(BdP-EHT), combined with a low bandgap nonfullerene acceptor (SMDPP) consisting of carbazole and diketopyrrolopyrrole units linked with a tetracyanobutadiene acceptor π-linker, was used to design bulk heterojunction polymer solar cells. After the optimization of the donor to acceptor weight ratio and solvent vapor annealing of the P(BdP-EHT):SMDPP active layer, the resulting polymer solar cell showed an overall power conversion efficiency of 9.29%, which is significantly higher than that for the polymer solar cell based on PC71BM (7.41%) processed under identical conditions. This improved power conversion efficiency is attributed to enhanced values of short circuit photocurrent and open circuit voltage, the better light harvesting efficiency of the P(BdP-EHT):SMDPP active layer in the near-infrared region, and the higher Lowest Unoccupied Molecular Orbital (LUMO) energy level of the SMDPP as compared to PC71BM, combined. Moreover, energy loss in the device based on P(BdP-EHT):SMDPP active layer is significantly low (0.48 eV) as compared to P(BdP-EHT):PC71BM counterpart (0.78 eV). Since the P(BdP-EHT) consists of triple bond, a linker may be beneficial for the stability of the polymer solar cells.