Isomeric Nonfullerene Acceptors: Planar Conformation Leading to a Higher Efficiency

Noncovalent conformational lock (NCL) is a beneficial noncovalent intramolecular interaction that assists in maintaining the molecular planar conformation. Such a planar conformation is favorable for a shorter molecular distance and higher molecular crystallinity, further yielding a more efficient charge transfer and higher power conversion efficiency (PCE). In this contribution, a pair of isomeric small-molecular nonfullerene acceptors (THP-4F and HPT-4F) were designed and synthesized based on the central core modification. HPT-4F with a negligible dihedral angle of 0.23° showed a highly planar conformation, bathochromic absorption, higher charge mobility, suppressed charge recombination, and enhanced Jsc and fill factor, leading to a PCE of 8.68%, nearly 8 times higher than 1.31% of its isomer THP-4F. This work gives a clear view of NCLs and molecular planarity for molecular design and efficient organic photovoltaic materials by comparing two structural isomers' totally different properties.