The fabrication, surface modification of TiO<sub>2</sub> nanorod arrays and their application in perovskite solar cells

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One dimensional TiO2 nanoarrays have attracted widely attention as electron transport materials in solar cells due to their direct electron transport route. In this paper, rutile TiO2 nanorod arrays were prepared by hydrothermal method and served as electron transport scaffold in organic-inorganic hybrid perovskite solar cells. The influence of introducing TiO2 compact layer on hydrothermal growth TiO2 nanorod arrays and photovoltaic performance of assembled soar cells was studied. The influences of nanorod length and TiCl4 treatment on microstructure of nanoarrays as well as photovoltaic performance of assembled soar cells were investigated. It was found that the introducing of TiO2 compact layer could induce growing ordered TiO2 nanorod arrays perpendicular to the substrate. An optimum TiO2 nanorod length is benefit to the rapid separation and transport of photo-excited carriers. The TiCl4 treatment of TiO2 nanorod arrays enhances the aspect-ratio of nanorod arrays and is accordingly possible to load more perovskite crystals and adsorb more light energy. Furthermore, the resulted nanoparticles from TiCl4 treatment could eliminate the cracks between perovskite crystal and TiO2 scaffold, and hence improve the interface and reduce the charge recombination, resulting in a higher photovoltaic performance. The optimum power conversion efficiency (PCE) of 15.11% was obtained in solar cell assembled with TiO2 nanorod arrays treated by 0.1 mol/L TiCl4 solution.