Synthesis, characterization and photovoltaic properties of benzo[1,2-b:4,5-b ']dithiophene-bridged molecules

Four new acceptor-donor-acceptor based organic small molecules with the benzo[1,2-b:4,5-b']dithiophene (BDT) unit as the central donor group, benzothiadiazole (BT) or fluoro-substituted benzothiadiazole as the acceptor, and different end-capping groups (BTBDT1-BTBDT4) have been synthesized and tested for solution-processed bulk-heterojunction organic solar cells. The absorption spectra, electronic energy levels, hole mobilities and solar cell performance of these compounds were investigated. All compounds show broad absorption in the visible range. The PCE of the solar cell device based on BTBDT3/PC71BM (1 : 2, w/w) reached 3.91% with a J(SC) of 10.08 mA cm(-2), a V-OC of 0.90 V and a FF of 0.43, under illumination of AM 1.5G, 100 mW cm(-2).