Comparing the Cubic and Tetragonal Phases of MAPbI₃ at Room Temperature

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Organic-inorganic perovskites face challenges in crystal structure stability for photovoltaic applications.
• Understanding phase-dependent properties is key to advancing perovskite solar cells.

Purpose of the Study:

• To comprehensively study the tetragonal and cubic phases of methylammonium lead iodide (MAPbI3) at room temperature.
• To elucidate the impact of organic cation dynamics on perovskite phase transitions.
• To compare the physical properties of MAPbI3's cubic and tetragonal phases under identical thermal conditions.

Main Methods:

• Utilized a significant shift in structural phase transition (ΔT = 62 K) to enable room-temperature studies.
• Compared MAPbI3 with all-inorganic CsPbI3 to isolate the role of organic cations.
• Evaluated electrical resistivity, charge carrier lifetime, photoluminescence (PL) quenching, and light absorption coefficient.

Main Results:

• The cubic phase of MAPbI3 exhibits a faster charge carrier lifetime compared to the tetragonal phase.
• Higher electrical resistivity and partial PL quenching were observed in the cubic phase, indicating increased trap-assisted nonradiative recombination.
• The cubic phase shows a larger light absorption coefficient in the green region than the tetragonal phase.

Conclusions:

• The distinct properties of MAPbI3's cubic and tetragonal phases are confirmed at room temperature, independent of phonon effects.
• Organic cation orientation and dynamics significantly influence the structural phase transition in hybrid perovskites.
• These findings offer insights for optimizing perovskite materials for enhanced photovoltaic device performance and stability.