Regulating Blend Miscibility by Adding Multifluorinated Polymer Acceptors Enables 18% Efficiency All-Polymer Solar Cells

Abstract

All-polymer solar cells (all-PSCs) are promising renewable energy sources. However, phase separation and molecular packing regulation are limited by both the poor miscibility between polymer donors (PDs) and polymer acceptors (PAs) and disordered polymer chain entanglements, leading to a dilemma in enhancing the performance of all-PSCs. Herein, three multifluorinated polymer acceptors (PY4F-C24, PY4F-C20, and PY4F-BO-C24) were designed and synthesized as the third component for the PM6:PY-IT host blend to address this issue. The fluorination strategy effectively reduces the surface energy of multifluorinated acceptors, thereby improving the miscibility of the blends and significantly reducing the phase separation in the ternary blends to a desirable value of ~20 nm. Moreover, multifluorinated polymer acceptors have more robust crystalline features, which can effectively enhance the crystallinity in ternary blends. The adjustment of alkyl chain length and conformation for multifluorinated polymer acceptors effectively controls the degree of crystallinity. The optimized blend morphology not only promotes exciton dissociation and charge transport, but also reduces energy loss, thus improving all three photovoltaic parameters simultaneously. Finally, the PM6:PY-IT:PY4F-C20-based blends exhibit more ordered molecular packing, and the corresponding ternary all-PSC achieves the highest power conversion efficiency (PCE) of 18.0%, which is a significant improvement compared to that of PM6:PY-IT device (15.2%).