Theoretical designing of small molecule donors for organic solar cells: Analyzing the effect of molecular polarity through structural engineering at terminal position

Abstract

Designing new small molecule donors is a hot top in organic solar cell research. Theoretical simulations can help in avoiding trial-and-error based designing, saving both resources and time. Herein, employing the density functional theory (DFT), we have designed four small molecule donors (SMDs) by replacing hydrogen of reference donor with fluorine, chlorine, bromine and cyano groups at the terminal position. This study provides new insights to understand the effect of molecular polarity on the structural, electronic, and optical properties of the designed SMDS. Using the DFT calculations, various important parameters including optimized geometries, HOMO and LUMO energy levels, bandgap energies, molecular electrostatic potentials, polarity indices were computed for all five molecules. Molecular dynamics (MD) simulations were performed to clearly visualize the (motion) interaction between the small molecule donors and phenyl-C17-butyric acid methyl ester (PC17BM) acceptor. Moreover, radial distribution function was utilized to analyze the attractions between molecules. In addition, similarity analysis was performed. The information about topology of positive and negative charges was obtained using Gasteiger charge analysis. The obtained results indicate that the effect of molecular polarity through cyano group was more appealing and effective than reference donor and other designed SMDs. © 2023 Elsevier B.V.