One‐Step Construction of a Perovskite/TiO 2 Heterojunction toward Highly Stable Inverted All‐Layer‐Inorganic CsPbI 2 Br Perovskite Solar Cells with 17.1% Efficiency

All‐layer‐inorganic perovskite solar cells (PSCs) are prized for their remarkable thermal stability and low cost. However, “imperfect contact” at the perovskite heterojunction hinders charge transport and causes photochemical deterioration, restricting photovoltaic performance, and operational stability. Herein, an efficient perovskite/TiO 2 heterojunction is constructed, produced by adding TiO 2 to an antisolvent to concurrently form a CsPbI 2 Br perovskite layer and a top TiO 2 electron transport layer in one step, which significantly improves the interfacial contact and thus facilitates charge transport at the heterojunction. The resultant inverted all‐layer‐inorganic PSCs exhibit a superior efficiency of 17.1%. Moreover, given the high‐quality perovskite/TiO 2 heterojunction and low interface defects, the encapsulated PSCs retain 91% or 92% of their initial efficiency for 1000 h under maximum power point tracking or damp‐heat conditions (85 °C and 85% relative humidity), respectively. Surprisingly, the unencapsulated PSCs maintain an initial efficiency of 86% during aging, even at 200 °C for 200 h.