Characterization of push-pull type of conjugated polymers containing 8H-thieno[2,3-b]indole for organic photovoltaics

Abstract Polymers using thieno[2,3- b ]indole (2-TI) with high planarity were synthesized and utilized for the photovoltaics. Conjugated polymers ( PTIDTBT, PTIFDTBT and PTIDFDTBT ) containing 2-TI as electron-donating unit and fluorinated DTBT as electron-accepting unit were synthesized. To enhance the effect of lowering highest occupied molecular orbital (HOMO) energy level for the high open-circuit voltages ( V OC ), we utilized new thieno[2,3- b ]indole (2-TI) moiety as the weak electron-donating group and the fluoro-substituted electron-accepting BT unit. The polymer composed of BT with two fluorine unit coupled with 2-TI, PTIDFDTBT , shows higher V OC out of the series. The device comprising PTIDFDTBT and PC 71 BM (1:3) showed a V OC of 0.79 V, a J SC of 8.39 mA/cm 2 , and a fill factor ( FF ) of 0.48, giving a power conversion efficiency of 3.21%.