Improvement of Characteristics of Metal Doped TiO₂ Thin Film and Application to Perovskite Solar Cell.

Over the past three decades, the development of renewable energy technologies has attracted significant attention to overcome both environmental pollution and global warming. Recently, a new type of solar cell based on an organic-inorganic halide perovskite material has been developed. Perovskite solar cells (PSC) were first reported in 2009; their efficiencies increased rapidly from 3.8% to 22%. PSCs have many advantages owing to their use of simple processing technology and stable materials. Perovskite materials have a general formula of ABX, where A is generally methyl ammonium CH₃NH (MA), B is a metal ion, such as Pb or Sn, and × represents a halogen ion. A distinct advantage of lead-based perovskites (i.e., MAPbX₃) is that their band gaps can be easily tuned, from 1.2 to 2.3 eV, by varying their compositions and anions. Titanium dioxide is as often used as an electron transport layer due to its high chemical and optical stability, non-toxicity, low cost, and resistance to corrosion. TiO₂ films can be characterized by the defects in their preparation, such as density fluctuations, pinholes, and cracks; these defects can reduce electrical conductivity and cause recombination. In this study, we have demonstrated that the electrical conductivity of TiO₂ thin films is improved by its doping with Al. When applied to a PSC, the doped thin film improves the charge transfer of the solar cell and increases its efficiency. Our results suggest that Al nanoparticles in the TiO₂ layer may contribute to the improvement of the PSC.