Effects of π-Bridge on Fused-Ring Electron Acceptor Dimers

Two nonfullerene acceptors (TTIDIC and BTIDIC), consisting of indacenodithiophene (IDT) dimers bridged with electron-rich thienothiophene (TT) or electron-accepting benzothiadiazole (BT), were synthesized and compared with their counterpart SIDIC without a bridge to study effects of the bridge nature. Their thin-film absorption spectra and bandgaps are similar. The electron-rich TT bridge slightly up-shifts, whereas the electron-poor BT bridge slightly down-shifts energy levels of the dimers. Both TT and BT bridges enhance the electron mobilities of the dimers. When using polymer J71 as an electron donor, SIDIC-, TTIDIC-, and BTIDIC-based photovoltaic cells show efficiencies of 9.71, 6.54, and 11.5%, respectively. Compared to TT bridge, the BT bridge improves photovoltaic performance of the dimers.