Domain‐Size‐Dependent Residual Stress Governs the Phase‐Transition and Photoluminescence Behavior of Methylammonium Lead Iodide

Abstract

Methylammonium lead iodide (MAPbI3) perovskite has garnered significant interest as a versatile material for optoelectronic applications. The temperature‐dependent photoluminescence (TDPL) and phase‐transition behaviors revealed in previous studies have become standard indicators of defects, stability, charge carrier dynamics, and device performance. However, published reports abound with examples of irregular photoluminescence and phase‐transition phenomena that are difficult to reconcile, posing major challenges in the correlation of those properties with the actual material state or with the subsequent device performance. In this paper, a unifying explanation for the seemingly inconsistent TDPL and phase‐transition (orthorhombic‐to‐tetragonal) characteristics observed for MAPbI3 is presented. By investigating MAPbI3 perovskites with varying crystalline states, ranging from polycrystal to highly oriented crystal as well as single‐crystals, key features in the TDPL and phase‐transition behaviors are identified that are related to the extent of crystal domain‐size‐dependent residual stress and stem from the considerable volume difference (ΔV ≈ 4.5%) between the primitive unit cells of the orthorhombic (at 80 K) and tetragonal phases (at 300 K) of MAPbI3. This fundamental connection is essential for understanding the photophysics and material processing of soft perovskites.

Quasi-Type II Core–Shell Perovskite Nanocrystals for Improved Structural Stability and Optical Gain

“…Moreover, theoretical calculations show that the tetragonal phase has a smaller band gap than the orthorhombic phase, which also supports this observation. It is noted that the phase transition temperature is lower than that in previous research works, , which may be due to the smaller size of the PeNCs. , The blue-shift of emission with temperature from 140 to 295 K can be described by the temperature coefficient α = ∂ E g /∂ T = 0.359 meV/K. This is mainly attributed to the thermal expansion (TE) of lattice due to the anharmonicity of the interatomic potentials. , In comparison, the PL peak position of the core–shell FAPbBr 3 /CsPbBr 3 PeNCs follows a continuous blue-shift from 50 to 295 K, which suggests that no phase transition takes place during this temperature range, likely due to the internal strain or a built-in electric field. , Moreover, negative thermal quenching only exists in FAPbBr 3 PeNCs as shown in Figure S1c,f, which implies more surface defect states of the material .…”

“…It is noted that the phase transition temperature is lower than that in previous research works, 35,36 which may be due to the smaller size of the PeNCs. 38,39 The blue-shift of emission with temperature from 140 to 295 K can be described by the temperature coefficient α = ∂E g /∂T = 0.359 meV/K. This is mainly attributed to the thermal expansion (TE) of lattice due to the anharmonicity of the interatomic potentials.…”

Stimuli-responsive switchable halide perovskites: Taking advantage of instability

“…Such performance could be achieved by using: (1) systems that switch preserving the perovskite structure, and/or (2) nanostructured perovskites where, due to their smaller particle sizes, switching times and structural stress caused by switching are expected to be lower than in bulk perovskites. [135][136][137] On the other hand, a switchable system should also retain any of its states for long periods of time. This aspect would particularly be important for non-volatile memory applications of halide perovskites.…”

Anomalous Structural Evolution and Glassy Lattice in Mixed‐Halide Hybrid Perovskites

“…[16] It is well established that the halide composition has a significant influence on the phase transitions in hybrid perovskites. The notable perovskite MAPbI 3 undergoes a transition from the cubic to the tetragonal phase near 330 K, and subsequently to an orthorhombic phase below 160 K. [17][18][19] In general, these phase transitions are detected through discontinuities in the dielectric permittivity and heat capacity, [13,20] solid-state nuclear magnetic resonance (NMR) line shapes, [21] and/or splitting of X-ray diffraction peaks. [18,22] Although hybrid perovskites are very promising for optoelectronic applications, they suffer from instability issues caused by a variety of factors such as humidity, high temperature, intense light, and even interfacial reactions.…”