High‐Purity Photoactive α‐Phase for Flexible Perovskite Photodetectors with Modified Electron Transport Layer

Abstract Regulating the crystallization process of organic–inorganic halide perovskite is essential for the fabrication of reproducible and efficient optoelectronic devices. Herein, a vacuum‐assisted heating treatment strategy for precursor is developed to obtain a high‐purity photoactive phase perovskite. By eliminating residual H 2 O molecules from raw materials and solvents, the method prevents the Pb–I framework of perovskite from being destroyed. Additionally, the pre‐treated precursor possesses high‐valence iodoplumbate species leading to preferable crystallization for perovskite films. Furthermore, a high on‐off ratio of 1103 is attained under 0 V and 550 nm illumination by employing a vertical n–i–p photodetector based on pure 𝛼‐phase perovskite films and interface passivation carried out by incorporating phenethylammonium hydroiodide (PEAI) in the n ‐type electron transport layer. The photodetector exhibits high sensitivity with the peak responsivity of 0.93 A W −1 and the detectivity of 1.55 × 10 12 Jones in the visible light range, making it a potential candidate for an imaging application. The flexible photodetector fabricated on polyethylene terephthalate (PET) substrate maintains 98.6% photocurrent density after 300 times of bending and preliminarily realizes imaging sensing. The heat‐treating strategy improves the adaptability of perovskite to complex environments and enables the preparation of reproducible pure 𝛼‐phase perovskite films, which boast enormous potential for optoelectronic applications.