A DFT/TD-DFT study on the π-spacer effect of coumarin 102-Based dyes for dye-sensitized solar cells applications

Abstract Developing new organic dyes with optimized electronic structures and superior light-harvesting capabilities is crucial for enhancing the efficiency of dye-sensitized solar cells (DSSCs). In the current study, four novel D- π -A organic dye molecules (MC1-MC4), with various π spacers, were designed based on Coumarin-102 dye to investigate their prospective uses in dye-sensitized solar cells (DSSCs). Therefore, DFT and TD-DFT calculations were utilized to explore the electronic structure and photophysical and photovoltaic properties of the designed dyes. Specifically, the optimized structures, electronic parameters, Frontier molecular orbitals (FMOs), Natural Bond Orbital (NBO) analysis, Density of States (DOS) analysis, and Global Reactivity Parameters (GRPs) were evaluated. The calculated values of the energy difference between HOMO and LUMO ranged from 2.63 to 2.97 eV, with the MC2 dye having the smallest band gap (2.63 eV). Furthermore, the influence of π spacers on the performance of DSSCs was studied by calculating the Non-Linear optical (NLO) characteristics, UV–vis spectra, and other important parameters determining the photovoltaic performance of DSSCs. The results show that MC2 exhibits the highest value of light-harvesting efficiency (0.96) and a more negative ΔG inject (−1.323 eV), indicating that MC2 would demonstrate a higher J SC and could theoretically be a better sensitizer of DSSC device.