A Benzobis(thiazole)-Based Copolymer for Highly Efficient Non-Fullerene Polymer Solar Cells

In recent years, non-fullerene polymer solar cells have attracted much attention due to their great potential for achieving high power conversion efficiencies, and in addition to the already existing donor polymers, varieties of excellent acceptors have been developed. To further improve the performance, the main challenge is now to identify perfect donor–acceptor pairs with suitable electronic properties and complementary optical absorption. In this article, we have investigated a donor–acceptor alternating copolymer poly[(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene)-2,6-diyl-alt-(2,6-bis(5-bromo-4-(2-butyloctyl) thiophen-2-yl)benzo[1,2-d:4,5-d′]bis(thiazole))] with benzo[1,2-d:4,5-d′]bis(thiazole) (BBT) as the accepting unit and benzo[1,2-b:4,5-b′]dithiophene as the donor unit. The polymer shows a wide band gap of 2.1 eV with absorption peaks at 515 and 554 nm, matching well with the strongest region of the solar radiation spectrum. A blend of this polymer with the narrow-bandga...