Effect of Ga Doping on Microwave-Assisted Synthesized TiO2 Nanoparticles and their Photovoltaic Performance as DSSC Photoanodes

Abstract Undoped and Ga-doped (1–16% nominal) anatase TiO2 nanoparticles were synthesized using a rapid microwave-assisted method and employed as photoanodes in dye-sensitized solar cells (DSSCs) sensitized with Z907 dye. Structural, morphological, optical, and textural characterizations (XRD, Raman, SEM, DRS, BET, UV–vis, and FTIR) revealed systematic Ga-induced modifications of the anatase TiO2 structure and progressive reduction in crystallite and particle sizes, together with a significant increase in specific surface area. Moderate nominal Ga content enhanced dye adsorption and visible-light harvesting without substantially modifying the TiO2 bandgap. Photovoltaic performance, evaluated by current density–voltage (J-V) and open-circuit voltage decay (OCVD) measurements, showed that the photoanode fabricated with 4% nominal Ga content performed best, achieving an approximately 60% enhancement in power conversion efficiency compared with undoped TiO2 devices. The improved photovoltaic response is attributed to enhanced light harvesting, improved charge injection, and reduced recombination losses, driven by favorable modification of the trap-state distribution and interfacial charge-transfer processes. In contrast, higher nominal Ga contents increased the distribution of deep trap states and inefficient semiconductor-dye coupling, reducing device performance. Stability tests conducted over 30 days confirmed that TiO2-based photoanodes with a nominal 4% Ga content exhibited the best long-term photovoltaic stability. The findings demonstrate that controlled Ga doping is an effective strategy for tailoring the physicochemical and electronic properties of TiO2 photoanodes and improving DSSC performance.