Novel phenothiazine-based sensitizers for high-performance dye-sensitized solar cells: enhanced photovoltaic properties through strategic Co-sensitization with N719

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This study presents a systematic investigation of novel phenothiazine-based sensitizers (SR1–6) for dye-sensitized solar cells (DSSCs), both as individual sensitizers and in co-sensitization with ruthenium-based N-719 dye. The compounds exhibited notable spectral properties when adsorbed on TiO2, demonstrating significant bathochromic shifts and broadened absorption profiles, indicative of strong electronic coupling with the semiconductor surface. Electrochemical characterization confirmed optimal energy level alignment, with ground state oxidation potentials (GSOP) ranging from −5.75 to −6.02 eV and excited state oxidation potentials (ESOP) between −3.54 and −3.77 eV, facilitating efficient electron injection and dye regeneration. In single-dye configurations, SR1 achieved the highest efficiency of 4.22% with a short-circuit current density (Jsc) of 11.96 mA cm−2, while co-sensitization with N-719 resulted in substantial improvements, particularly for SR6 + N-719, which attained 9.77% efficiency with a Jsc of 21.63 mA cm−2. Electrochemical impedance spectroscopy revealed that successful co-sensitized devices exhibited enhanced charge transfer resistance (Rct) values, indicating reduced electron recombination and improved interface stability. This comprehensive study provides valuable insights into molecular design strategies for efficient DSSC sensitizers and demonstrates the efficacy of strategic co-sensitization approaches.