Large polarons in lead halide perovskites

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• Lead halide perovskites exhibit excellent optoelectronic properties attributed to defect tolerance.
• The role of large polaron formation in these properties and the necessity of organic cations are not fully understood.

Purpose of the Study:

• To investigate the formation mechanism and dynamics of large polarons in lead bromide perovskites.
• To determine the influence of cation type (organic vs. inorganic) on polaron formation.

Main Methods:

• Time-resolved spectroscopy to observe polaron formation in real-time.
• First-principles calculations to model polaron formation and identify contributing factors.

Main Results:

• Large polarons predominantly form via deformation of the [PbBr3]- framework, independent of the cation.
• Polaron formation time differs significantly between methylammonium lead bromide (CH3NH3PbBr3) at 0.3 ps and cesium lead bromide (CsPbBr3) at 0.7 ps.
• First-principles calculations confirmed the Pb-Br-Pb deformation modes as the cause and quantitatively explained the rate differences.

Conclusions:

• The soft [PbX3]- sublattice is crucial for charge carrier protection in lead halide perovskites.
• Inorganic and mixed-cation perovskites offer potential for enhanced stability and tunable optoelectronic properties without mechanistic limitations.