A review from fullerene dominance to non-fullerene innovation: theoretical perspective on next-generation organic photovoltaics.

The mechanical flexibility, solution processability, and the capability for low-cost processing of organic photovoltaics (OPVs) make them a viable class of next-generation solar energy technology. The design of effective electron acceptors that promote exciton dissociation, charge transfer, and long-term device stability is a key feature in finding OPV performance. With a focus on their electronic structure, charge-transfer mechanisms, and structure-property connections, this analysis offers theoretical insights into the fabrication of electron acceptors from traditional fullerene derivatives to sophisticated non-fullerene acceptors (NFAs). The creation of NFAs has been fueled by the restricted tunability, weak visible absorption, and morphological instability of fullerene-based acceptors, which have previously dominated because of their suitable energy levels and isotropic charge transmission. Studies using density functional theory (DFT) and time-dependent DFT (TD-DFT) show how end-group engineering, frontier orbital distribution, and molecule geometry in NFAs improve charge mobility, exciton separation, and light absorption. Additionally, theoretical models demonstrate how important molecular planarity, π-π stacking, and dipole moments are in controlling donor-acceptor interfacial energetics and blend morphogenesis. When taken as a whole, these computational insights offer a basic framework for the logical development of next-generation acceptors targeted at increased photostability, lower energy losses, and higher power conversion efficiencies in OPVs.