Effect of electron-withdrawing units on triphenylamine-based small molecules for solution-processed organic solar cells

Organic small molecules (TPA-BT3T, TPA-PT3T, and TPA-DFBT3T) using triphenylamine as a donor unit, terthiophene as a bridge, and benzo-2,1,3-thiadiazole (BT), [1,2,5]thiadiazolo[3,4-c]pyridine (PT) or 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT) as an acceptor unit were designed and synthesized through Suzuki coupling reactions. These molecules exhibited good thermal stability with decomposition temperatures over 380 A degrees C and broad absorption from 300 to 700 nm. Photovoltaic devices were fabricated with these small molecules as donors and PC71BM as an acceptor. The TPA-BT3T based devices exhibited a power conversion efficiency of 2.89%, higher than those of the TPA-PT3T- and TPA-DFBT3T-based devices (1.34% and 1.54% respectively). The effects of electron-withdrawing units on absorption, energy level, charge transport, morphology, and photovoltaic properties also were investigated.