Thienothiophene-benzoxadiazole based conjugated copolymer for organic photovoltaic application

Abstract In present study a novel conjugated polymer of alternating thienothiophene and benzoxadiazole based units (poly(TT-alt-DTOT)) is synthesized and characterized. The polymer shows excellent thermal stability, good solubility and exhibit an optical band gap of ∼1.81 eV. Density functional theory (DFT) calculation of poly(TT-alt-DTOT) indicates that highest occupied molecular orbital (HOMO) is completely delocalized throughout the polymer and the lowest unoccupied molecular orbital (LUMO) is localized mainly along its acceptor part. Furthermore bulk heterojunction solar cells were fabricated using poly(TT-alt-DTOT) as donor and fullerene derivative (PC60BM and PC70BM) as the acceptors. Preliminary device study of the fabricated device shows a power conversion efficiency of 2.06% with a short circuit current density of 8.8 mA cm−2, an open circuit voltage of 0.76 V. This polymer can be further optimized for efficient photovoltaic material.