Carrier Diffusion and Recombination Anisotropy in the MAPbI₃ Single Crystal

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• Methylammonium lead iodide (MAPbI3) is a key perovskite semiconductor for optoelectronics.
• Charge-carrier diffusion and recombination are critical performance metrics.
• Defects and crystal orientation significantly impact carrier dynamics and energy losses.

Purpose of the Study:

• To investigate photoexcited carrier diffusion and recombination in large-sized MAPbI3 single crystals (SCs) with exposed crystal planes.
• To understand the influence of crystal orientation and growth conditions on carrier behavior.
• To explore the formation of homophylic p-n junctions at crystal ledges.

Main Methods:

• Growth of large-sized MAPbI3 SCs with simultaneously exposed (110), (112), (100), and (001) planes by adjusting PbI2 to methylammonium iodide (MAI) ratios.
• Characterization of SCs' semiconductor properties and Fermi levels.
• Time-resolved fluorescence microscopy to study photoexcited carrier diffusion and recombination.

Main Results:

• MAPbI3 SCs exhibited weak n-type semiconductor character with differing Fermi levels across planes, forming homophylic p-n junctions.
• Planes (110) and (001), favored by higher MAI concentrations, showed red-shifted photoluminescence, longer carrier lifetimes, and enhanced diffusion lengths.
• Carrier diffusion from (001) and (112) planes facilitated extraction at grain boundaries/ledges, though excessive MAI increased radiative recombination.

Conclusions:

• Crystal plane orientation critically influences charge-carrier diffusion and recombination in MAPbI3.
• Optimized MAI ratios can enhance carrier diffusion length and photorecycling, improving optoelectronic performance.
• Understanding anisotropic carrier dynamics is vital for designing efficient perovskite-based devices.