A mechanistic investigation of non-covalent interactions induced by selenium and alkoxy substitution in the structural and photoelectric properties of non-fused ring electron acceptors

Abstract

The pivotal role of non-covalent interactions has been increasingly acknowledged by researchers in the intricate design and advancement of non-fused ring electron acceptors (NFREAs). This surge in attention arises from their profound influence on the facilely twisted molecular geometries and critical photoelectric attributes inherent to organic solar cells (OSCs). In this study, various selenium atoms and alkoxy groups were strategically introduced into the well-performing NFREA A4T-16, leading to the creation of molecules denoted as Se-1 to Se-9 and O1 to O9. Utilizing density functional theory (DFT) and time-dependent density functional theory (TD-DFT), a comprehensive analysis of these molecules was conducted, encompassing factors such as intramolecular non-covalent interactions, the fill factor (FF), and the open-circuit voltage (V_OC). The electronic structures and photovoltaic characteristics of these molecules underwent a thorough investigation to elucidate the intricate mechanisms governing non-covalent interactions within NFREAs, thereby clarifying their functional significance. The findings disclose that acceptor molecules featuring selenium substitution display notably augmented Se∙∙∙O and S∙∙∙O non-covalent interactions, exceeding the strength observed in their alkoxy-substituted derivatives. This results in the selenium-substituted derivatives boasting superior overall planarity, narrower energy gaps, reduced excitation energies, and broader absorption bandwidths, thereby enhancing their charge transfer characteristics compared to A4T-16. Conversely, the alkoxy-substituted acceptor molecules display higher fill factor (FF) and superior open-circuit voltage (V_OC) relative to the selenium-substituted derivatives. Notably, the innermost substitutions at O6, O7, and O9 show the most promising outcomes, potentially indicating optimal power conversion efficiency (PCE).