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

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) 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 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 donor (or acceptor) based bulk heterojunction is partial to AIM with high γ. Our results not only highlight the important role of template molecular weight in the regulation of PEDOT γ, but also suggest guidelines to match photoactive bulk heterojunction materials with proper AIMs.