Template molecular weight-dependent PEDOT surface energy: impact on the photovoltaic performance of bulk-heterojunctions

Abstract

Tailoring the template structure is attractive for the realization of high-performance poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymers; however, precious little attention has been paid to the molecular weight effect of templates on the surface energy (γ_s) of PEDOTs. Herein, on the basis of the represent template of polystyrene sulfonic acid, we demonstrate that increasing the template molecular weight is effective to increase the size of PEDOT-rich domains and thus decrease the γ_s of PEDOT films, for the first time. After fabrication into organic solar cells with the synthesized PEDOT series as anode interfacial materials (AIMs), we found that PBDB-T:Y6, PM6:Y6, D18-Cl:Y6 and PM6:BTP-ec9 based binary bulk heterojunctions present optimal miscibility and photovoltaic performance (12.96%, 17.21%, 17.30% and 18.19%, respectively) on various AIMs, and the high γ_s donor (or acceptor) based bulk heterojunction is partial to AIM with high γ_s. Our results not only highlight the important role of template molecular weight in the regulation of PEDOT γ_s, but also suggest guidelines to match photoactive bulk heterojunction materials with proper AIMs.