Two-Dimensional Conjugated Benzo[1,2-B:4,5-B ']Diselenophene-Based Copolymer Donor Enables Large Open-Circuit Voltage And High Efficiency In Selenophene-Based Organic Solar Cells

A two-dimensional electron-rich fused-ring moiety (ClBDSe) based on benzo[1,2-b:4,5-b ']diselenophene is synthesized. Three copolymers (PBDT-Se, PBDSe-T, and PBDSe-Se) are obtained by manipulating the connection types and number of selenophene units on the conjugated main chains with two 2D fused-ring units and two different pi-bridges, respectively. In comparison with PBDT-Se and PBDSe-Se, PBDSe-T with benzo[1,2-b:4,5-b ']diselenophene unit and thiophene pi-bridge exhibits the deepest HOMO energy level and the strongest crystallinity in neat films. The PBDSe-T:Y6 blend film exhibits the best absorption complementarity, the most distinctive face-on orientation with proper phase separation, the highest carrier mobilities, and the lowest charge recombination among three blend films. Finally, the PBDSe-T:Y6-based device delivers an impressive power conversion efficiency (PCE) of 14.50 %, which is higher than those of PBDT-Se:Y6 and PBDSe-Se:Y6. Moreover, a decent open-circuit voltage (V-oc) of 0.89 V with a remarkably small energy loss of 0.44 eV is achieved for PBDSe-T:Y6. The efficiency of 14.50 % is the highest value for selenophene-containing copolymer-based binary organic solar cells (OSCs). This study provides evidence that introduction of 2D-benzo[1,2-b:4,5-b ']diselenophene as a fused electron-rich unit with pi-bridging into copolymeric donors is a valid strategy for providing high V-oc and excellent PCE simultaneously in selenophene-based OSCs.