Tailoring Interface\nvia Tuning the Phase and Morphology\nof TiO<sub>2</sub> for Efficient Mesoporous Perovskite Solar Cells

The efficiency of mesoporous perovskite solar cells (mp-PSCs)\nis\nsignificantly influenced by favorable charge transport properties\nacross their various interfaces. The interfaces involving compact-TiO<sub>2</sub>, mesoporous electron transport layer (ETL), and perovskite\nlayer are particularly vital for high-performing devices. Our study\npresents a combined experimental and computational approach, specifically\nemploying density functional theory, to explore the impact of mesoporous-ETL/perovskite\ninterface properties on carrier transport. These properties are examined\nin relation to the phases and morphologies of the mesoporous layer.\nDifferent phases of TiO<sub>2</sub>, including anatase, rutile, and\nbrookite, and various morphologies such as nanocubes, nanorods, and\ndisks/clusters, were synthesized using a simple hydrothermal synthesis\nroute. They constitute the mesoporous layer, and Cs<sub>0.05</sub>FA<sub>0.84</sub>MA<sub>0.14</sub>PbI<sub>2.55</sub>Br<sub>0.45</sub> is used as the perovskite absorber in mp-PSCs. The performance of\nthe resulting mesoporous-TiO<sub>2</sub> (mp-TiO<sub>2</sub>) device\nwas investigated in relation to the different phases and morphologies\nof mp-TiO<sub>2</sub>. The mp-PSCs with the anatase phase as the mesoporous\nETL exhibited the highest device parameters, including power conversion\nefficiency of 19.15%, short-circuit current density of 22.55 mA/cm<sup>2</sup>, fill factor of 76.50%, and open-circuit voltage of 1.11\nV. The superior performance of the anatase structure is attributed\nto its promising band edge alignment, which results from a small negative\nconduction band offset compared to other phases, thereby enhancing\ncarrier transport. This study underscores the potential of interface\noptimization to improve device performance. By investigating the device\nperformance across different phases and morphologies of the mp-TiO<sub>2</sub> layer, we can pave the way for the design of next-generation\nenergy devices.