Modulation of phase separation and molecular stacking in ternary organic solar cells by introducing a guest polymer with excellent miscibility with host polymer

Abstract

Proper miscibility between polymer donor and nonfullerene acceptor (NFA) to form a desired photoactive layer morphology is one of the key prerequisites to achieving efficient organic solar cells (OSCs). The ternary strategy provides a straightforward and effective approach for adjusting the miscibility of different components. For benzo [d][1,2,3] triazole (BTA) −based polymers, their photovoltaic properties largely lag behind those of other classical polymers. We tried different kinds of small molecule receptors as the third component, but the results were not satisfactory, and then focused the selection of the third component on the polymer donor. In this study, we incorporated the wide-band gap polymer PM6 as a guest polymer to the F10-fu:Y18 combination, both of which contain BTA unit. PM6 is preferentially miscible with F10-fu, and the addition of PM6 reduces the miscibility of the donor materials with Y18. This adjustment allows simultaneous optimization of phase separation and molecular stacking, leading to the formation of nanoscale charge transport channels. Consequently, the power conversion efficiency (PCE) of F10-fu:PM6:Y18-based ternary device reached 17.39%, obviously higher than that of F10-fu:Y18-based binary device (16.34%) and PM6:Y18-based binary device (16.23%). These improvements can be attributed to extended light absorption range, cascade energy levels, superior morphology, and favorable charge dynamics. Our study offers guidance for the regulation mechanism of ternary OSCs driven by miscibility based on two donor polymers/ one acceptor molecule system.