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 TiO2 at room temperature using titanium halide precursors and employed it as an electron collector. Uniform and dense TiO2 was formed without using vacuum processes by the oxidation of TiI4 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.