Elizabeth Adzo Addae

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.

The influence of ZnO nanolayers as a passivating layer prevents electrons from recombining with the electrolyte or oxidized dye molecules at the interface by acting as a blocking layer for semiconducting materials. At 300 °C, it was observed that FTO-ZnO 500-cycle samples recorded the lowest Rq and Ra values of 1210 nm and 0.877 nm, respectively, resulting in homogeneous, crystalline, and smooth surface thin films. SEM images of FTO-ZnO 500 cycles-300 °C (150.00 KX) show a much more crystalline and homogeneous layer, while FTO-ZnO 500 cycles-100 °C (150.00 KX) show an irregular and agglomerated surface. Energy-dispersive spectroscopy also revealed that ALD successfully deposited ZnO on the FTO glass substrates, especially at 300 °C, resulting in uniform layers. In visible light wavelength (400 nm–800 nm), FTO-ZnO 500 cycles-300 °C exhibited the highest stable transmittance value of 0.78 a.u. However, it can be observed that the temperature with the slowest grain growth at 500 cycles of ZnO deposition was 200 °C, with a layer thickness of 60 nm. The device efficiency increased progressively with deposition temperature, reaching a maximum power conversion efficiency of 4.63% for ZnO films deposited at 300 °C with 500 ALD cycles. The observed enhancement is attributed to improved crystallinity, grain growth, and film uniformity at elevated deposition temperatures, which collectively enhance charge transport and reduce recombination losses. These results demonstrate that optimizing the ALD temperature is a key factor in achieving high-quality ZnO films and improved DSSC performance.

In dye-sensitized solar cells (DSSCs), materials classified as Transparent Conducting Oxides (TCOs) have the capacity to conduct electricity and transmit light at the same time. Their exceptional blend of optical transparency and electrical conductivity makes them popular choices for transparent electrodes in DSSCs. Fluorine Tin Oxide (FTO) was utilized in this experiment. The optical and electrical characteristics of TCOs may be negatively impacted by their frequent exposure to hostile environments and potential for deterioration. TCOs are coated with passivating layers to increase their performance, stability, and defense against environmental elements including oxygen, moisture, and chemical pollutants. Because of its superior dielectric qualities, strong chemical stability, and suitability with TCO materials, aluminum oxide (Al₂O₃) was utilized as a passivating layer for the FTO. In this research work, Al₂O₃ was deposited via atomic layer deposition (ALD) to form thin mesoporous layers as a passivator in the photoanode (working electrode). The work focuses on finding an appropriate thickness of Al₂O₃ for optimum performance of the dye-sensitized solar cells. The solar simulation and sheet resistance analysis clearly showed 200 cycles of Al₂O₃ to exhibit an efficiency of 4.31%, which was the most efficient performance. The surface morphology and topography of all samples were discussed and analyzed.