Near room temperature approaches for the preparation of air-stable and crystalline CH₃NH₃PbI₃

This work demonstrates an exotic role of CH₂Cl₂ in a formation of stable phase of highly crystalline CH₃NH₃PbI₃ perovskite, on a bulk scale. In the first method, a partially-reacted product obtained after co-grinding of precursors viz. CH₃NH₃I and PbI₂was sonicated in CH₂Cl₂ to form pure phase of CH₃NH₃PbI₃. In second method, the precursors in γ-Butyrolactone were treated with CH₂Cl₂ to form crystalline and phase-pure CH₃NH₃PbI₃. X-ray Diffraction analysis confirmed the formation of stable and highly crystalline tetragonal phase of CH₃NH₃PbI₃ perovskite having space group I4cm. Well-defined rhombo-hexagonal dodecahedron crystals were seen in SEM and TEM images. Exceptional air stability of CH₃NH₃PbI₃ so forms are attributed to adsorption of CH₂Cl₂. Optical band gaps obtained from the diffused reflectance spectra (Kubelka–Munk analysis), matched very well with the one estimated from Cyclic Voltammetry (CV). Valence band and conduction band edge positions estimated from the CV analysis are in good agreement with the one reported from UV photoelectron spectroscopy. Both the samples gave steady state fluorescence at ca. 750 nm with quantum yields in the range 15–35.5%. - Highlights: • A role of CH₂Cl₂ is brought out in formation of stable CH₃NH₃PbI₃ perovskite. • Cyclic voltammetry has been used to estimate the band edge positions. • Excellent fluorescence quantum yield, underlines the minimal structural defects.