Highly Efficient All-Polymer Solar Cells based on Wide Bandgap Donor Copolymers Containing Selenophene Moieties

Abstract

All-polymer solar cells (all-PSCs) based on binary blends of napthalenediimide biselenophene acceptor copolymer (PNDIBS) with wide-bandgap selenophene-containing donor copolymers, PBDB-S and PBDBS-T, were fabricated and characterized to investigate the effects of alkylselenyl side-chain and selenophene p-spacer on the respective polymer donors and compared to their thiophene equivalent, PBDB-T. Compared to PBDB-S, PBDBS-T displayed a narrower bandgap and red-shifted absorption owing to an upshifted HOMO by 0.13 eV. Both donors displayed significantly enhanced hole mobilities compared to PBDB-T, resulting in significantly higher photocurrent values of 17.51 mA/cm2 and 18.31 mA/cm2. Additionally, the superior crystallinity, and phase-separated morphology conferred by PBDBS-T resulted in efficient exciton dissociation and charge transport, enabling greater fill factors up to 63.5% and 9.5% efficiency. These results indicate that a selenophene p-spacer in a D-A polymeric backbone is beneficial to the photovoltaic properties, photophysics, and morphology of all-PSCs and is a promising molecular design strategy to develop highly efficient all-PSCs.