A DFT Study on the Impact of Saturated and Conjugated Side Chains on the Optoelectronic Performance of Y-series Nonfullerene Acceptors

Abstract

Organic photovoltaic (OPV) consisting of nonfullerene acceptors have been found to be excellent candidates for harnessing solar energy. Extensive studies are being carried out to modify structures in a number of ways to enhance their efficiency. These include modifications in the acceptor part, use of efficient backbones and insertion of pi spacers. One strategy is the attachment of donor side chains for better assembly of molecules. In this work, the effect of theoretically designed side chains on electrochemical and optical properties of OPVs was studied. A series of molecules consisting of saturated (SC1-4) and conjugated donor (CD1-2) were designed and studied computationally for their potential OPV properties. Parameters like Band gap, absorption spectrum, frontier molecular orbital distribution, binding energy, fill factor, open circuit voltage, excitation energies, density of states (DOS) and transition density matrix (TDM) were studied using DFT and TD-DFT methods. Unsaturated side chains although exhibit better performance in terms of open circuit voltage and hole mobility but reduce light harvesting efficiency. All saturated side chain modifications showed improvement in fill factor and open circuit voltage than reference molecule. SC3 modification with red shift and smaller band gap showed the best performance.