Exploration of 4-substituted thiophene-based azo dyes for dye-sensitized solar cells and non-linear optical materials: synthesis and an in silico approach

Abstract

This work examines the effects of changing the secondary donors’ donating strengths at the thiophene ring's fourth position in a range of dyes designated SR1 to SR9. The DFT results indicate that the molecular planarity is greatly affected by the placement of the secondary donor at position four, which changes the charge transfer (CT) characteristics in the thiophene-azo-salicylic acid backbone. These results are corroborated by TD-DFT analysis, which indicates that as the secondary donor's donating strength increases, so does the vertical absorption maximum. Based on the computed photovoltaic characteristics, these dyes perform better from SR1 to SR5. Research on dye@TiO₂ clusters suggests a potential for binding with TiO₂, which might cause the dye@TiO₂ clusters’ absorbance to shift red. Additionally, computed linear and non-linear optical (NLO) properties exhibit similar trends to those observed for DSSC performance. The experimental results, which include HOMO and LUMO energies as well as initial absorption in dimethylformamide (DMF), match very well with the patterns seen in DFT and TD-DFT calculations. The high thermal stability of SR1 to SR4 is indicated by thermogravimetric analysis (TGA), indicating their practical applicability in non-linear optics (NLO) and DSSC applications. The efficiencies of the produced DSSCs vary; SR4 has the highest efficiency (4.50 ± 0.1), and SR1 has the lowest (0.37 ± 0.1). The combined effects of theoretical and experimental DSSC results demonstrate the vital role of secondary donors in influencing molecular characteristics and NLO and DSSC performance.