New indolo carbazole-based non-fullerene n-type semiconductors for organic solar cell applications

In this work, two new indolo-[3,2-b]-carbazole (ICz) core-based non-fullerene acceptors (ICz-Rd(2) and ICz-RdCN(2)) with an A-pi-D-pi-A backbone were designed, synthesized, and characterized and the influence of molecular engineering on the terminal end groups on their performance in organic solar cells (OSCs) was systematically examined. The ICz-Rd(2) and ICz-RdCN(2) acceptors showed strong and wide-ranging absorption profiles from 350-800 nm in solution and film with high molar extinction coefficients of 6.6 x 10(4) M-1 cm(-1) and 1.0 x 10(5) M-1 cm(-1), respectively. These acceptors were employed along with a low band gap D-A conjugated polymer P as a donor for polymer solar cells and, after optimization of the active layers, the P:ICz-Rd(2)- and P:ICz-RdCN(2)-based devices offered overall power conversion efficiencies of 7.88% and 9.76%, which are higher than that of their PC71BM-processed counterpart ( 5.89%). The enhanced power conversion efficiencies for these non-fullerene acceptors may be related to the wide absorption spectra of the active layers and their low voltage loss.