Visualizing Buried Local Carrier Diffusion in Halide Perovskite Crystals via Two-Photon Microscopy

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Halide perovskites exhibit excellent optoelectronic properties, making them promising for light emission and solar energy applications.
• Current device performance is hindered by microscale variations in photophysical properties, affecting charge carrier dynamics.
• Efficient charge collection in photovoltaic devices relies heavily on understanding charge carrier diffusion.

Purpose of the Study:

• To investigate the influence of microscale heterogeneities on charge carrier diffusion in halide perovskites.
• To develop and apply a novel technique for spatially resolved analysis of diffusion processes.
• To correlate local diffusion coefficients with material properties like trap density and morphology.

Main Methods:

• Development of a photoluminescence tomography technique integrated with confocal microscopy.
• Utilizing one- and two-photon excitation for distinguishing surface and bulk charge carrier diffusion.
• Characterization of methylammonium lead bromide single crystals to measure local diffusion coefficients.

Main Results:

• Observed a wide distribution of local diffusion coefficients, ranging from 0.3 to 2 cm²·sâ��¹.
• Demonstrated that diffusion coefficients are highly dependent on local trap density and morphological environment.
• Highlighted that these critical diffusion details are undetectable by macroscopic or surface-only measurements.

Conclusions:

• Microscale heterogeneities significantly impact charge carrier diffusion pathways in halide perovskites.
• The developed photoluminescence tomography technique provides a new framework for understanding diffusion sensitivity to local properties.
• Accurate characterization of buried defects and local properties is essential for optimizing perovskite-based devices.