Novel unsymmetrical squaraine dyes for dye-sensitized solar cells: Synthesis, characterization, and comparative photovoltaic performance of USQI-NPh2Me2 and USQI-OMe

This study presents the synthesis, characterization, and photovoltaic performance of two novel unsymmetrical squaraine dyes, USQI-NPh2Me2 and USQI-OMe, engineered for application in dye-sensitized solar cells (DSSCs). These chromophores were functionalized with distinct electron-donating groups, di-p-tolylamine for USQI-NPh2Me2 and methoxy for USQI-OMe. Their molecular structures were confirmed through FT-IR, 1HNMR, 13C NMR, and mass spectrometry. Comprehensive photophysical and electrochemical studies were conducted to fine-tune the HOMO and LUMO energy levels of both dyes, optimizing charge injection into the TiO2 conduction band and facilitating dye regeneration with the iodolyte (I₃⁻/I⁻) redox mediator. USQI-NPh2Me2 exhibited a strong absorption maximum at 661 nm, achieving a high short-circuit current density (JSC) of 13.17 mA/cm2, an open-circuit voltage (VOC) of 0.71V, and an overall efficiency of 7.01 %. USQI-OMe, with its absorption peak at 651 nm, reached a JSC of 11.88 mA/cm2, a higher VOC of 0.72 V, but a slightly lower overall efficiency of 6.41 %. Both dyes demonstrated reduced aggregation on the TiO2 surface, contributing to enhanced DSSCs performance. A Comparative analysis revealed that USQI-NPh2Me2 exhibits higher efficiency, while USQI-OMe provided a greater voltage output, highlighting the influence of electron-donating groups on photovoltaic properties. These findings provide valuable insights into structure-property relationships in unsymmetrical squaraine dyes, paving the way for future DSSCs chromophore design and optimization. •Two novel unsymmetrical squaraine dyes with different electron-donating groups were synthesized for DSSCs applications.•USQI-NPh2Me2 achieved 7.01% efficiency with 13.17 mA/cm² JSC, while USQI-OMe reached 6.41% efficiency with higher VOC.•Both dyes showed excellent photostability and reduced aggregation on TiO2, improving DSSCs performance.•The study underscores the role of electron-donating groups in photovoltaic properties for DSSCs chromophore design.