Carbazole-Substituted Triphenylamine and Diketopyrrolopyrrole Alternating Copolymer for Photovoltaic Cells

A new alternating conjugated polymer (PTCDPP) of carbazole-substituted triarylamine and diketopyrrolopyrrole is prepared and characterized in detail. The polymer exhibits two strong absorption bands at 345 and 600 nm. With highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of -5.13 eV and -3.67 eV, PTCDPP displays an energy gap of 1.66 eV. PTCDPP-based bulk heterojunction solar cells with a structure of fluorinated tin oxide (FTO)/TiO2/PTCDPP:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/MoO3/Ag are fabricated. The devices are optimized by adjusting the composition of the PTCDPP:PCBM active layer, thermal treatment, and addition of processing additives. The device based on PTCDPP:PCBM (1:4, w/w) shows a power conversion efficiency (PCE) of 2.31%, with a short-circuit current of 4.17 mA cm(-2), an open-circuit voltage of 0.79 V, and a fill factor of 0.35. The best cell performance (2.65% PCE) is achieved by using 1,8-diiodooctane (3%, v/v) as a processing additive and annealing the active layer at 80 degrees C.