Synthesis and characterization of phenathrothiadiazole-based conjugated polymer for photovoltaic device

A new accepter with phenanthro[9,10-c][1,2,5]thiadiazole unit was synthesized and utilized for the synthesis of the conjugated polymers, PCPDTDTPT and PCDTPT, containing electron donor–acceptor pairs for OPV devices. This novel phenanthro[9,10-c][1,2,5]thiadiazole unit with phenanthene group can supply planarity and possess electron deficient thiadiazole group. The solid films of PCPDTDTPT and PCDTPT show absorption bands with maximum peaks at 492 and 394 nm and the absorption onsets at 620 and 519 nm, corresponding to band gaps of 2.00 and 2.39 eV, respectively. The HOMO and LUMO levels of PCPDTDTPT and PCDTPT were estimated to be (−5.54, −3.63) and (5.81, 3.65) eV, respectively. The PCDTPT with carbazole moiety shows lower HOMO levels as compared to PCPDTDTPT caused by strong electron donating ability of nitrogen atom to provide higher Voc. The devices with PCPDTDTPT: PC71BM with TiOx layer showed a VOC of 0.77 V, a JSC of 4.71 mA/cm2, and a FF of 0.36, giving a power conversion efficiency of 1.24%.