Synthesis and photovoltaic property of donor–acceptor type conjugated polymer containing carbazole and 4,7-dithiazolylbenzothiadiazole moiety utilized as a promising electron withdrawing unit

A donor–acceptor type low band gap conjugated polymer that was composed of carbazole and 4,7-dithiazolylbenzothiadiazole (DTzBT), i.e. Poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thiazol-2′,1′,3′-benzothiadiazole)] (PCDTzBT), was synthesized through the Suzuki coupling polymerization for organic photovoltaics. According to the simulated electronic properties, the synthesized polymer exhibited a better balanced energy level than the polymer that included the 4,7-dithienylbenzothiadiazole (DTBT) moiety. In optical and electrochemical experiments, it exhibited a band gap as low as 1.85 eV and well balanced HOMO and LUMO energy levels of −5.54 and −3.65 eV, respectively. A PCE of 0.448% was observed in the device that used the PCDTzBT/PC71BM blend film as the active layer. In spite of the well-balanced energy level and low band gap, it is believed that the low PCE value depended on the low molecular weight.