Inverted-Structured Perovskite Solar Cells with a TiO₂ Electron-Collector Layer Formed at Room Temperature from Titanium Halide Solutions

Organohalide perovskites are promising light-harvesting materials for solar cells because of their ease of synthesis and high performance. P-i-n-structured perovskite solar cells have the advantage of a low processing temperature (<150 °C) for applications in flexible solar cells. However, they are limited by the high cost and low stability of fullerene electron collectors. In this study, we developed a solution-based method for synthesizing TiO 2 at room temperature using titanium halide precursors and employed it as an electron collector. Uniform and dense TiO 2 was formed without using vacuum processes by the oxidation of TiI 4 in ambient air. A power conversion efficiency (PCE) of 12.6% was obtained. Our study paves the way for synthesizing efficient and affordable solar cells at a mass scale.