Transition from Light-Induced Phase Reconstruction to Halide Segregation in CsPbBr_3-xI Nanocrystal Thin Films

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• Inorganic metal-halide perovskites offer promising applications due to their efficiency and low cost.
• Light-induced ion migration in mixed-halide perovskites causes bandgap instability, hindering device performance.
• Understanding phase transitions in CsPbBr3-xIx is crucial for stabilizing perovskite optoelectronics.

Purpose of the Study:

• To elucidate the transition mechanism between phase reconstruction and segregation in CsPbBr3-xIx nanocrystal thin films.
• To investigate the role of halide migration in CsPbBr3-xIx under light exposure.
• To determine thermodynamic parameters governing phase transitions in these perovskite systems.

Main Methods:

• Combined hyperspectral fluorescence microspectroscopy and computational modeling.
• Analyzed kinetic parameters using linear unmixing data and Fick's second law.
• Investigated Br-I interdiffusion behavior with laser-induced temperature increases.

Main Results:

• Samples with x=1.0 and x=1.5 showed halide migration and Br enrichment, forming CsPbBr3 via photo/thermal activation.
• Thermodynamic parameters like activation energy and diffusibility were quantified.
• Br-I interdiffusion followed Arrhenius-like behavior with increasing temperature.
• Samples with x=2.0 exhibited phase segregation due to nanocrystal size, iodine content, and high laser intensity.
• Phase segregation in CsPbBrI2 formed a type-II heterostructure, causing a red-shifted fluorescence spectrum.
• Real-time dark recovery of light-induced halide segregation was observed in CsPbBrI2.

Conclusions:

• Photo/thermal activation drives halide migration and CsPbBr3 phase reconstruction in specific compositions.
• Laser intensity, nanocrystal size, and iodine content dictate the transition to phase segregation.
• The study provides insights into stabilizing perovskite materials for optoelectronic applications.