Enhanced performance of organic photovoltaic cells fabricated with a methyl thiophene-3-carboxylate-containing alternating conjugated copolymer

A new donor-acceptor copolymer, containing benzodithiophene (BDT) and methyl thiophene-3-carboxylate (3MT) units, is designed and synthesized for polymer solar cells (PSCs). The 3MT unit is used as an electron acceptor unit in this copolymer to provide a lower highest occupied molecular orbital (HOMO) level for obtaining polymer solar cells with a higher open-circuit voltage (V _OC). The resulting bulk heterojunction PSC made of the copolymer and [6,6]-phenyl-C71-butyric acid methyl ester (PC ₇₁BM) exhibits a power conversion efficiency (PCE) up to 4.52%, a short circuit current (J _SC) of 10.5 mA·cm- ², and a V _OC of 0.86 V. A new donor-acceptor type copolymer containing methyl thiophene-3-carboxylate is designed and synthesized to obtain a lower highest occupied molecular orbital (HOMO) level and strong inter- or intra-molecular interaction between polymers. The photovoltaic device based-on this copolymer exhibits a power conversion efficiency up to 4.52% and an open-circuit voltage of 0.86 V.