Understanding the Cubic Phase Stabilization and Crystallization Kinetics in Mixed Cations and Halides Perovskite...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Formamidinium (FA) lead halide perovskites undergo a detrimental phase transition, hindering their application in solar cells.
• Alloying with methylammonium (MA) perovskites can prevent this transition, but the mechanism remains unclear.

Purpose of the Study:

• Investigate the principles for stabilizing the pure α-phase perovskite structure.
• Understand the mechanism by which MA alloying inhibits the α-to-δ phase transition.
• Optimize perovskite composition for enhanced solar cell performance.

Main Methods:

• Growth of high-quality mixed cation and halide perovskite single crystals (FAPbI3)1-x(MAPbBr3)x.
• Compositional analysis using Powder X-ray Diffraction (XRD) and Single Crystal XRD.
• Characterization of phase stability and electronic properties using Fourier-Transform Infrared Spectroscopy (FT-IR) and carrier lifetime measurements.

Main Results:

• Identified optimal composition range (x = 0.1-0.15) for a stable α-phase perovskite without segregation.
• Achieved a carrier lifetime of 11.0 μs in the mixed perovskite, over 20 times that of pure FAPbI3.
• Demonstrated that MA+ incorporation tunes the Goldschmidt tolerance factor and lowers Gibbs free energy.
• Showed Br incorporation controls crystallization kinetics and reduces defect density, inhibiting the δ-phase.

Conclusions:

• MA+ and Br incorporation are critical for stabilizing the α-phase perovskite structure.
• Understanding these stabilization principles enables the fabrication of high-quality perovskite crystals.
• The optimized composition and crystal growth led to perovskite solar cells with a record efficiency of 19.9%.