Dithieno[3,2-b:2′,3′-d]pyrrole and benzothiadiazole-based semicrystalline copolymer for photovoltaic devices with indene-C60 Bisadduct

Abstract

A semicrystalline low-bandgap polymer (PDTPBT) based on alternating dithienopyrrole and benzothiadiazole moieties as a pair of the indene-C 60 bisadduct (ICBA) for polymeric solar cells is reported. The lowest unoccupied molecular orbital (LUMO) level of PDTPBT is measured to be -3.47 eV, ensuring sufficient energy offset for photoinduced charge transfer to ICBA. Photovoltaic cells are fabricated with ICBA and [6,6]-phenyl-C 71-butyric acid methyl ester (PC71BM) as an acceptor. By replacing PC71BM with ICBA, the open-circuit voltage is increased by 0.23 V and the resulting power conversion efficiency is improved from 1.17% to 1.71%. To optimize the ICBA-based devices, crystalline low-bandgap structures should be designed carefully as a pair of ICBA by considering the energy-level offset for charge separation and crystalline interchain ordering, for minimizing the intercalated ICBAs inside the polymer domain. A semicrystalline copolymer based on dithienopyrrole and benzothiadiazole is investigated as an active layer with the indene-C60 bisadduct (ICBA) for photovoltaic devices. A low-bandgap structure should be carefully designed as a pair of ICBA by considering the energy level offset for exciton separation and crystalline ordering for minimizing the intercalated ICBAs inside the polymer domain.