Effects of Thermal Modification of Cerium-Doped Black Titanium Dioxide Nanoparticles for Improved Light Absorption in Perovskite Solar Cells

In this paper, cerium-doped black titanium dioxide (Ce-black-TiO₂) nanoparticles were successfully synthesized via a sol-gel method followed by hydrogenation and subsequent thermal treatment at 450°C, 650°C, 850°C, and 1050°C. The structural, morphological, and opto-chemical properties were systematically investigated using x-ray diffraction (XRD), photoluminescence (PL), ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, Ce-black-TiO₂ was employed as an electron transport layer in the fabrication of perovskite solar cell devices to evaluate the influence of thermal treatment on photovoltaic performance. XRD results revealed a transition from a poorly crystalline anatase phase to a well-crystallized rutile phase with increasing temperature, accompanied by an increase in crystallite size from 3.5 to 29.0 nm. UV-Vis analysis demonstrated a red shift in absorption and bandgap narrowing from 3.10 to 2.47 eV, indicating enhanced light harvesting capability. PL measurements showed reduced charge recombination at moderate annealing temperatures. When integrated into perovskite solar cells, Ce-black-TiO₂ achieved a maximum power conversion efficiency of 5.0%, more than three times higher than the as-prepared sample (1.44%). These findings demonstrate that cerium doping, combined with controlled thermal modification, significantly enhances the optoelectronic properties of black TiO₂, offering a promising strategy for improving the performance of perovskite solar cells.