Synthesis and photophysical properties of -alkyl dithieno[3,2-:2',3'-]pyrrole based donor/acceptor-π-conjugated copolymers for solar-cell application.

Two kinds of donor-acceptor π-conjugated copolymer based on poly{[-hexyl-dithieno(3,2-:2',3'-)pyrrole-2,6-diyl]-[isoindigo]} (PDTP-IID) and poly{[-hexyl-dithieno(3,2-:2',3'-)pyrrole-2,6-diyl]-[thiazol-2,5-diyl]} (PDTP-Thz) were investigated. These copolymers were synthesized a Stille coupling reaction. The results showed the structure-property relationships of different donor-acceptor (D-A) combinations. The polymer structures and photophysical properties were characterized by H NMR, TGA, DSC, UV-vis absorption spectroscopy, AFM, CV, and XRD measurement. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it showed that the copolymers exhibit not only a low bandgap of 1.29 eV and 1.51 eV but also a deep highest occupied molecular orbital (HOMO) of -5.49 and -5.11 eV. Moreover, photovoltaic properties in combination with the fullerene derivatives were investigated. The device based on the copolymers with PCBM exhibited higher maximum power conversion efficiency and higher maximum short-circuit current density of 0.23% with 1.64 mA cm of PDTP-IID:PCBM and 0.13% with 1.11 mA cm of PDTP-Thz:PCBM than those of the copolymers with PCBM. Measurements performed for -hexyl-dithieno(3,2-:2',3'-)pyrrole-based copolymers proved the potential of these polymers to be applied in optoelectronic applications.