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

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 H₂O 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 × 10¹² 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.