Conjugated donor–acceptor terpolymers entailing the Pechmann dye and dithienyl-diketopyrrolopyrrole as co-electron acceptors: tuning HOMO/LUMO energies and photovoltaic performances

Abstract

Three conjugated D–A terpolymers PBPD1, PBPD2, and PBPD3 with the Pechmann dye-derived electron acceptor and dithienyl-diketopyrrolopyrrole as co-acceptors are presented. Their HOMO/LUMO energies and absorptions can be tuned by varying the ratios of two acceptors. Importantly, HOMO energies of these terpolymers are lowered by increasing the content of the Pechmann dye-derived electron acceptor in the conjugated backbones. The thin blend films of PBPD1, PBPD2, and PBPD3 with PC₇₁BM have been tested as active layers for polymer solar cells. The blend of PBPD1:PC₇₁BM shows a high power conversion efficiency of up to 5.21%, which is higher than that with the blend of the dithienyl-diketopyrrolopyrrole-based polymer without the Pechmann dye-derived electron acceptor and PC₇₁BM. In addition, the neat thin films of PBPD1, PBPD2, and PBPD3 exhibit ambipolar semiconducting properties with hole and electron mobilities up to 0.604 cm² V⁻¹ s⁻¹ and 0.225 cm² V⁻¹ s⁻¹.