Asymmetric Glycolated Substitution for Enhanced Permittivity and Ecocompatibility of High-Performance Photovoltaic Electron Acceptor

Traditional organic photovoltaic materials exhibit low dielectric constants (epsilon(r)) of 3 to 4, restricting the further enhancement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein we design and synthesize a fused-ring electron acceptor named Y6-4O through introducing an asymmetric highly polarizable oligo(ethylene glycol) side chain onto the pyrrole unit of Y6. Compared with alkylated Y6 (epsilon(r) = 3.36), asymmetric glycolated Y6-4O shows a notably higher er value of 5.13 and better solubility in nonhalogen solvents. Because of the higher er value, the devices based on as-cast PM6:Y6-4O processed using toluene exhibit a higher charge separation yield, slower bimolecular recombination kinetics, and less voltage loss relative to the control devices based on PM6:Y6. Consequently, a high PCE of 15.2% is achieved for PM6:Y6-4O-based devices, whereas the PM6:Y6-based devices show PCEs of only 7.38%. 15.2% is the highest PCE for the as-cast nonhalogenated processed OSC devices, and it is also much higher than the values (<8.5%) reported for OSCs based on high-permittivity (epsilon(r) > 5) organic photovoltaic semiconductors.

Automated summary

By designing and synthesizing a novel organic photovoltaic material named Y6-4O with an asymmetric oligo(ethylene glycol) side chain, the dielectric constant is increased and better solubility in nonhalogen solvents is achieved. Compared to traditional materials, the PM6:Y6-4O devices based on Y6-4O exhibit higher power conversion efficiencies.