End-group engineering of non-fused benzothiadiazol derivatives with thiophene rings based small donor molecules for tuning the photovoltaic properties via DFT approach

Abstract

In this study, seven new small-donor molecules (U1-U7) with an A2-(D-A1)2-D-A2 configuration, were developed by end-groups manipulations for the betterment of photon absorption, charge mobility and morphology of photovoltaic molecules. The CAM-B3LYP functional, along with 6-31G(d,p) basis set had been exploited to probe the optical, as well as electronic characteristics of UR and U1-U7molecules. In addition, the solvent state calculations were analyzed by employingthe time-dependent approach (TD-DFT) of the theoretically used density functional theory (DFT). It was observed that all the newly developed molecules (U1-U7) possessed a redshift in their λmax, and also had smaller bandgap with better charge mobility for electrons due to their lower RE energy of λe than the reference molecule (UR). Additionally, several optoelectronic characteristics of the examined molecules were compared tothose of the well-known Y6 fused ring-based acceptor. All the newly created molecules exhibited lesser excitation energy, as well as greater oscillator strength than UR molecule. Another optical property, the light harvesting efficiency (LHE) had a range of 0.99935–0.99985 for all studied molecules. Open circuit voltage (VOC) was estimated by forming a combination of the newly developeddonor moleculeswith PC61BM. Some of the developed compounds revealed an increase in open circuit voltage, as well as the fill factor (FF), and consequently the estimated power conversion efficiencies (PCEs). Among all other newly developed molecules, U1 exhibited excellent optoelectronic properties such as maximum absorption, smallest Eg, charge mobility, and highest FF. Therefore, these end-capped manipulated compounds, especially U1, mightbe considered in the manufacturing of exceptionally competent organic solar cells in the near future.