Electrochemical Impedance Spectroscopy Analysis and DFT Study of Fabricated DSSCs Used Carbazole‐Based Dyes

Abstract In this study, we present the synthesis and characterization of two carbazole‐based dyes (1ThCzSA and 2ThCzSA) for dye‐sensitized solar cell (DSSC) applications. Both dyes incorporate thiophene as a π‐spacer and cyanoacrylic acid as the electron acceptor. Their photophysical, electrochemical, and theoretical properties were analyzed via UV–vis, cyclic voltammetry, and density functional theory (DFT) calculations. Electrochemical impedance spectroscopy (EIS) revealed charge recombination dynamics, with recorded efficiencies of 0.18% for 1ThCzSA and 0.34% for 2ThCzSA under AM 1.5 illumination. Corresponding electron lifetimes were 1.20 and 1.65 ms. The Lowest Unoccupied Molecular Orbital (LUMO) levels of both dyes were suitably positioned for effective electron injection into TiO 2 . Uniquely, these monomers were evaluated without using chenodeoxycholic acid (CDCA) as a co‐adsorbent, and their EIS characteristics had not been previously reported. Computational analyses, including molecular electrostatic potential (MEP), noncovalent interaction (NCI), electron localization function (ELF), and localized orbital locator (LOL), provided further insight into their electronic properties. Notably, the D–(π–A) 2 configuration of 2ThCzSA led to broader light absorption compared to the D–π–A structure of 1ThCzSA. Overall, the study underscores how molecular architecture, especially functional group positioning and π‐bridge arrangement, affects photovoltaic performance. These findings support the potential of carbazole‐based dyes in advancing DSSC efficiency for future molecular design.