TiO 2 Colloid‐Spray Coated Electron‐Transporting Layers for Efficient Perovskite Solar Cells

TiO 2 is one of the most efficient and widely used materials for electron‐transporting layer (ETLs) in perovskite solar cells (PSCs). The formation of efficient TiO 2 layers is generally carried out at high temperature by baking at a temperature >400 °C or by vacuum deposition (e.g., atomic layer deposition and E‐beam). In this study, the preparation of a TiO 2 ETL for PSCs is reported with excellent properties at low temperatures based on the synthesis of a stable TiO 2 colloidal aqueous solution and spray coating. The prepared TiO 2 colloids are able to produce a dense and uniform ETL even if it is simply dried at 100 °C after spray coating. It is believed that this is owing to the peroxo functional group remaining on the surface of the TiO 2 colloids. The TiO 2 ETLs, combined with the TiO 2 underlayer formed by chemical bath deposition, and the sprayed TiO 2 colloids allowed the fabrication of PSCs with performance similar to those of PSCs produced by annealing at 450 °C with a TiO 2 paste. The PSCs fabricated entirely at 100 °C demonstrated power conversion efficiency of 22.7% in small cells, and 19.0% in mini‐modules.