Theoretical Study on Functionalizing A-D-A Type Non-Fullerene Acceptor by Fused Rings and Side Chains for Organic Solar Cells

The modification of fused rings in the central backbone, side chains, and end groups of the non-fullerene acceptor (NFA) for organic solar cells (OSCs) can modulate properties and photovoltaic performance. In order to investigate the effect of fused rings and side chains on photovoltaic performance, PBDB-T is selected as electron donor and IDTIC, IDIC, IDIC-PhC6, IDIC-C4Ph, 4TIC, ITIC-OE, IDTTIC, ITC6-IC, ITIC, and C8-ITIC are selected as NFAs. Based on quantum chemistry calculations, the geometries, electronic structures, excitation properties, excited-state lifetimes, and electrostatic potentials (ESPs) of the monomer and the PBDB-T:NFA complexes are studied, and the rate constants of charge transfer (CT), exciton dissociation (ED) and charge recombination (CR) processes are analyzed. The results show that the increase of fused-ring in NFA's backbone by substituting phenyl or thienyl with bithiophene can elevate the highest occupied molecular orbital energies, reduce the gap of frontier molecular orbital energies, induce red-shift of absorption spectrum, increase CT energy, improve CT and ED rates. This work provides a detailed understanding of tuning optoelectronic properties and photovoltaic performance by modifying NFA's side chains and extending backbones. IDTIC, IDIC, IDIC-PhC6, IDIC-C4Ph, 4TIC, ITIC-OE, IDTTIC, ITC6-IC, ITIC, and C8-ITIC are studied to understand how to adjust photovoltaic performance by modifying acceptor's fused rings and side chains.image