Inverted-Structured\nPerovskite Solar Cells with a\nTiO<sub>2</sub> Electron-Collector Layer Formed at Room Temperature\nfrom Titanium Halide Solutions

Organohalide perovskites are promising light-harvesting\nmaterials\nfor solar cells because of their ease of synthesis and high performance.\nP-i-n-structured perovskite solar cells have the advantage of a low\nprocessing temperature (<150 °C) for applications in flexible\nsolar cells. However, they are limited by the high cost and low stability\nof fullerene electron collectors. In this study, we developed a solution-based\nmethod for synthesizing TiO<sub>2</sub> at room temperature using\ntitanium halide precursors and employed it as an electron collector.\nUniform and dense TiO<sub>2</sub> was formed without using vacuum\nprocesses by the oxidation of TiI<sub>4</sub> in ambient air. A power\nconversion efficiency (PCE) of 12.6% was obtained. Our study paves\nthe way for synthesizing efficient and affordable solar cells at a\nmass scale.