Simple and Environmentally Friendly Solution Synthesis of CsPbI 3 Nanoribbons: Investigating the Reversible δ‐ to γ‐Phase Transition

The all-inorganic lead halide perovskites, including cesium lead iodide (CsPbI3), have attracted significant attention due to their possible applications in photovoltaics, light-emitting devices, and other optoelectronic technologies, driven by their intrinsic optoelectronic properties. This study introduces a simple, green, and scalable solution synthesis method for the CsPbI3 perovskite fabrication, utilizing beta-diketonate [Cs(hfa)]n and [Pb(hfa)2diglyme]2 precursors and ethanol as solvent. The as-synthesized nanoribbons are initially fabricated in the pure yellow delta-phase, as confirmed by X-ray diffraction and energy-dispersive X-ray analysis. Thermal analysis through differential scanning calorimetry highlights the reversible phase transition from delta-CsPbI3 to the black cubic alpha-phase. The photoactive and metastable black gamma-CsPbI3 is obtained via high-temperature annealing and rapid cooling under inert conditions. Optical characterizations have been performed in order to extrapolate a bandgap of 2.89 eV for the delta-phase and 1.62 eV for the gamma-phase, while the photoluminescence analysis displays intense emissions at 530 and 700 nm for the delta- and gamma-phase, respectively. Ambient photoemission spectroscopy further elucidates the energy levels of the gamma-phase, determining a highest occupied molecular orbital energy of 5.68 eV and a work function of 4.32 eV. These findings demonstrate the possibility to synthesize pure CsPbI3 and obtain the gamma-CsPbI3 phase with promising applications.