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

Two kinds of donor-acceptor π-conjugated copolymer based on poly{[ N -hexyl-dithieno(3,2- b :2',3'- d )pyrrole-2,6-diyl] alt -[isoindigo]} (PDTP-IID) and poly{[ N -hexyl-dithieno(3,2- b :2',3'- d )pyrrole-2,6-diyl] alt -[thiazol-2,5-diyl]} (PDTP-Thz) were investigated. These copolymers were synthesized via 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 1 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 PC 71 BM exhibited higher maximum power conversion efficiency and higher maximum short-circuit current density of 0.23% with 1.64 mA cm -2 of PDTP-IID:PC 71 BM and 0.13% with 1.11 mA cm -2 of PDTP-Thz:PC 71 BM than those of the copolymers with PC 61 BM. Measurements performed for N -hexyl-dithieno(3,2- b :2',3'- d )pyrrole-based copolymers proved the potential of these polymers to be applied in optoelectronic applications.