TiO₂/ZnO nanocomposites with a metal-free dye and a polymer gel electrolyte: optimizing photovoltaic efficiency and assessing stability via time series analysis

As part of the rapidly advancing field of energy technologies, solar energy-driven studies using nanomaterials have gained significant attention. In this context, designing dye-sensitized solar cells (DSSCs) with nanostructured titania (TiO₂) and its composites is a key focus in material selection. This study investigated the synthesis and photovoltaic performance of TiO₂ nanoparticles (NPs) and their composites with ZnO nanorods (NRs), synthesized via a one-step ex situ approach. The fabricated devices were evaluated using a metal-free SK3 dye (D-π-A carbazole) and a Co²⁺/Co³⁺-based polymer gel electrolyte. Structural properties were analyzed using Rietveld refinement, alongside other physicochemical characteristics. Notably, the TiO₂/ZnO nanocomposite (TZ-3 NCs) with 30 wt% ZnO NRs in the photoanode demonstrated a significant improvement in solar energy-conversion efficiency (η) of 4.3%, which was 1.8 times higher than that of the TiO₂/SK3 NC-based photoanode (2.38%). This enhancement was attributed to the reduced charge-transfer resistance, improved donor density, and increased surface area, facilitating efficient charge transport. Additionally, the study explored the stability of the TZ-3/SK3 NC-based photoanode using time series analysis, a statistical tool that can contribute to understanding its long-term performance.