Asymmetric non-fullerene acceptors enable high photovoltaic performance via the synergistic effect of carbazole-terminated alkyl spacer and halogen substitution

Abstract

High-performance non-fullerene acceptors (NFAs) are valuable for promoting the power conversion efficiency of organic solar cells (OSCs). Particularly, owing to their adjustable surface tension and molecular packing, asymmetric NFAs are promising for the development of novel organic photovoltaic materials. Herein, three novel asymmetric NFAs, namely Y6-SCz1, Y6-SCz2, and Y6-SCz3, have been designed and synthesized by rationally tuning the branching position of the carbazole-terminal side-chains on the pyrrole ring along with varying halogen substitutions on the indanone end-groups. Consequently, in the PM6:Y6-SCz2 combination, the systematically optimized absorption, energy level, Flory–Huggins interaction parameters, and charge transport process generate a champion PCE of 15.60% with a high open-circuit voltage (V_OC) of 0.87 V in OSCs. Our findings deliver new insights into the molecular design of asymmetric NFAs, which are of great importance for further practical implementation of OSCs.