| Summary: | In mesoscopic perovskite solar cells (PSCs) the recombination processes within the TiO<sub>2</sub> photoelectrode and at the TiO<sub>2</sub>/perovskite interface limit power conversion efficiency. To overcome this challenge, we investigated the effect of TiO<sub>2</sub> phase composition on the electronic structure of TiO<sub>2</sub> photoelectrodes, as well as on PSCs performance. For this, a set of PSCs based on TiO<sub>2</sub> thin films with different content of anatase and rutile particles was fabricated under ambient conditions. X-ray diffraction, optical spectroscopy and scanning electron microscopy were used to study the structural, morphological and optical characteristics of TiO<sub>2</sub> powders and TiO<sub>2</sub>-based thin films. X-ray photoelectron spectroscopy (XPS) analysis of anatase revealed a cliff conduction band alignment of 0.2 eV with respect to the rutile. Energy band alignment at the anatase/rutile/perovskite interfaces deduced from the XPS data provides the possibility for interparticle electron transport from the rutile to anatase phase and the efficient blocking of electron recombination at the TiO<sub>2</sub>/perovskite interface, leading to efficient electron-hole separation in PSCs based on mixed-phase TiO<sub>2</sub> photoelectrodes. PSCs based on TiO<sub>2</sub> layers with 60/40 anatase/rutile ratio were characterized by optimized charge extraction and low level of recombination at the perovskite/TiO<sub>2</sub> interface and showed the best energy conversion efficiency of 13.4% among the studied PSCs. Obtained results provide a simple and effective approach towards the development of the next generation high efficiency PSCs.
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