Secondary Hydrothermally Processed Engineered Titanium Dioxide Nanostructures for Efficient Perovskite Solar Cells

A secondary hydrothermal process was used to synthesize exotic hollow nanostructures of rutile TiO 2 as an electron‐transport layer for perovskite solar cells. The prepared nanostructures were used in combination with methylammonium lead iodide (MAPbI 3 ) perovskite, and their photovoltaic properties were studied. This core–shell architecture of a perovskite enveloped by TiO 2 provides an enhanced surface area, better contact with the perovskite because of the larger adsorption area, and effective light penetration. Our results revealed that the hollow nanoflowers exhibit a photocurrent density of 21.05 mA cm −2 , an open‐circuit voltage of 0.916 V, and a fill factor of 0.66, which leads to a power conversion efficiency of 12.72 %. These results were also verified by electrochemical impedance spectroscopy and time‐resolved photoluminescence spectroscopy. Furthermore, the effect of the wetting time was studied, and our results revealed that a minimum time of 100 s is required for good penetration of a MAPbI 3 /γ‐butyrolactone solution.