High Extinction Coefficient Thieno[3,4-b]thiophene-Based Copolymer for Efficient Fullerene-Free Solar Cells with Large Current Density

A thieno[3,4- b ]thiophene-based donor polymer PTBTz-2 was employed to construct fullerene-free solar cell with the classical acceptor ITIC. Interestingly, due to the high extinction coefficients and wide absorption for these two materials, the active layer can harvest a larger fraction of the coverage solar spectrum even in ultrathin film. Furthermore, the simultaneous advantages of appropriate cascade energy level, well-balanced hole/electron mobility (μ h /μ e = 1.16), and low charge accumulation and recombination, make the PTBTz-2/ITIC-based solar cells exhibit an excellent power conversion efficiency of 10.92% with large short circuit current density of 20.34 mA cm –2 . The results indicate that fine-tailored thieno[3,4- b ]thiophene-based polymers would be another type of promising donor materials, except for widely reported efficient benzo[ d ][1,2,3]triazole (BTA)- or benzo[1,2- c:4,5- c ′]-dithiophene-4,8-dione (BDD)-based polymers, and would enrich the reservoir of high-performance light-harvesting conjugated polymers.