Emulsion–Demulsion Route to MAPbI ₃ Perovskite Thin Films for Optical Energy Transducer Application

We report the synthesis of methylammonium lead iodide (MAPbI 3 ) thin films via an emulsion–demulsion (E-LARP) route and provide a comprehensive evaluation of their structural, optical, and optoelectronic properties with emphasis on stability and energy transduction performance. X-ray diffraction and transmission electron microscopy confirm the tetragonal I 4/ mcm phase with nanocrystalline ordering, while elemental mapping and surface analyses reveal intrinsic Pb–I bonding alongside pronounced environmental reactivity. Pristine films exhibit a sharp absorption onset near 770–780 nm and strong photoluminescence consistent with a direct bandgap of ∼1.55 eV. Under ambient exposure, optical degradation is marked by hydrate-phase transitions, PbI 2 formation, and defect-state emissions, underscoring the material’s sensitivity to moisture and oxygen. Temperature-dependent photoluminescence further reveals a tetragonal-to-orthorhombic transition below ∼160 K, accompanied by exciton localization and phonon-coupled broadening. Device prototyping with FTO/MAPbI 3 /Ag heterojunctions demonstrates diode-like rectification, high photosensitivity (∼8.3), and measurable quantum efficiency, though photocurrent decay under continuous illumination reflects intrinsic photoinstability. Collectively, these multitechnique investigations establish the emulsion–demulsion route as a viable pathway for MAPbI 3 thin films in optoelectronic applications, while emphasizing the critical need for encapsulation, compositional engineering, and interface passivation to achieve long-term operational stability.