Vacuum-Controlled Growth of CsPbI₂Br for Highly Efficient and Stable All-Inorganic Perovskite Solar Cells

A high-temperature annealing process (>250 °C) is always needed to obtain high-quality α-CsPbI₂Br perovskite films, which makes it a challenge in the manufacture and application of flexible photovoltaic devices. In this work, a vacuum-controlled growth (VCG) method that can effectively control the crystallization of perovskite and provide high-quality films with larger grain size and low defect density at a lower temperature is demonstrated. Besides, a facile introduction of polyethyleneimine ethoxylated (PEIE) interlayer improves the charge extraction and suppresses the carrier recombination. Therefore, the power conversion efficiency (PCE) of an all-inorganic CsPbI₂Br perovskite solar cell (PSC) reaches 12.32%. The unencapsulated PSCs with VCG treatment and PEIE modification show outstanding stabilities while retaining over 95% of the initial PCE after being stored in a N₂ glovebox for 1000 h. This low-temperature crystallization method and cheap interlayer introduction can drive the development of future commercialization of all-inorganic perovskite solar cells.