Defect, Morphology, and Interface Engineering of TiO2 in Dye Sensitized Solar Cells: Recent Progress and Perspectives

Dye-sensitized solar cells (DSSCs) remain promising low-cost photovoltaic technologies because of their simple fabrication, tunable optical properties, and effective operation under low-light conditions. Titanium dioxide (TiO2) is the most widely used photoanode material in DSSCs owing to its chemical stability, suitable band alignment, low toxicity, and excellent transparency. However, the photovoltaic performance and long-term stability of TiO2-based DSSCs are still limited by charge recombination, slow electron transport, interfacial losses, and structural degradation. This review summarizes recent advances in defect engineering, morphology engineering, and interface engineering of TiO2 photoanodes for high-performance DSSCs. Attention is given to the role of oxygen vacancies, Ti3+ states, metal/non-metal doping, and heterostructure formation in tailoring the electronic structure and charge transport behavior of TiO2. The influence of various TiO2 nanostructures, including nanoparticles, nanotubes, nanorods, nanosheets, and hierarchical architectures, on dye adsorption, light scattering, electron mobility, and recombination dynamics is critically discussed. Furthermore, recent progress in interface engineering strategies such as passivation layers, blocking layers, MXene incorporation, composite photoanodes, and atomic layer deposition are examined in relation to interfacial charge transfer and device stability. Current challenges involving defect-induced recombination, morphology-related transport trade-offs, and long-term degradation are also analyzed. Finally, future perspectives on hierarchical nanoarchitectures, multifunctional interfaces, flexible DSSCs, and hybrid TiO2 systems are presented. This review provides an integrated understanding of how defect, morphology, and interface engineering collectively govern the performance of TiO2 photoanodes and offers design guidelines for next-generation high-efficiency and stable DSSCs.