Synergistic steric–dipole modulation via stepwise trifluoromethyl substitution enables active-layer hierarchical assembly and >20% power conversion efficiency in organic photovoltaic devices

A stepwise trifluoromethyl substitution strategy is developed for the structural modification of small-molecule acceptors. The device based on –C(CF 3 ) 3 functionalized CHE-9F achieves an efficiency of 20.30%.