Direct Observation of Size-Dependent Phase Transition in Methylammonium Lead Bromide Perovskite Microcrystals and Nanocrystals

Abstract

Methylammonium (MA) lead halide perovskites have been widely studied as active materials for advanced optoelectronics. As crystalline semiconductor materials, their properties are strongly affected by their crystal structure. Depending on their applications, the size of MA lead halide perovskite crystals varies by several orders of magnitude. The particle size can lead to different structural phase transitions and optoelectronic properties. Herein, we investigate the size effect for phase transition of MA lead bromide (MAPbBr 3 ) by comparing the temperature-dependent neutron powder diffraction patterns of microcrystals and nanocrystals. The orthorhombic-to-tetragonal phase transition occurs in MAPbBr 3 microcrystals within the temperature range from 100 to 310 K. However, the phase transition is absent in nanocrystals in this temperature range. In this work, we offer a persuasive and direct evidence of the relationship between the particle size and the phase transition in perovskite crystals.

Charge Carrier Recombination Dynamics in MAPb(BrxCl1–x)3 Single Crystals

“…In addition, we note the change of the 545 and 575 nm peak positions with temperature is no longer continuous at ∼140 K, as shown in the inset of Figure a. From temperature-dependent single-crystal X-ray diffraction studies of MAPbBr 3 , , we infer that the transition from orthorhombic to tetragonal occurs at 140–150 K and that from tetragonal to cubic occurs at 230–240 K. The observed sharp change in peak position at ∼140 K agrees with the phase transition temperature from orthorhombic to tetragonal. , Additionally, a broad emission band appears in the wavelength range of 570–800 nm when the temperature is <140 K and can be attributed to the emission from the emissive defect state at the crystal structure of the orthogonal phase. , …”

“…From temperaturedependent single-crystal X-ray diffraction studies of MAPbBr 3 , 41,42 we infer that the transition from orthorhombic to tetragonal occurs at 140−150 K and that from tetragonal to cubic occurs at 230−240 K. The observed sharp change in peak position at ∼140 K agrees with the phase transition temperature from orthorhombic to tetragonal. 41,42 Additionally, a broad emission band appears in the wavelength range of 570−800 nm when the temperature is <140 K and can be attributed to the emission from the emissive defect state at the crystal structure of the orthogonal phase. 41,43 For the PL of MAPbBr 3 single crystal above 140 K, with the tetragonal phase crystal structure, the integrated intensities of PL emission peaks at ∼545 and ∼575 nm increase with a decrease in temperature (Figure 5c), which fits the thermally activated carrier trapping model.…”

Mechanism of isosymmetric polar order–disorder phase transition in pyroelectric [CH3CH2NH3]2NaGa(HCOO)6 double perovskite

“…[1][2][3][4][5] In some hybrid perovskites, a few intriguing physical phenomena can simultaneously coexist making them appealing for a wide range of applications. 2,[5][6][7] In particular, the simplest halide 3D lead-based perovskites comprising the smallest organic cations, including methylammonium (MA + ), [8][9][10] fluoromethylammonium (FMA + ), 11 formamidinium (FA + ), [12][13][14] methylhydrazinium (MHy + ), 15,16 and aziridinium (AZR + ), 17 exhibit excellent optical properties for optoelectronic photovoltaic, light emitting, and lasing applications, including tuneable bandgaps, second-harmonic generation (SHG), excitonic emission, long carrier diffusion lengths, high mobility, and high absorption coefficients. 1,5,18,19 Due to a rather scarce choice of molecular cations forming 3D lead halide perovskites and lead toxicity, perovskites with other metal ions and longer organic linkers, such as formates, hypophosphites, azides, cyanides, and dicyanamides, are of considerable relevance.…”

Nature of Self-Trapped Exciton Emission in Zero-Dimensional Cs2ZrCl6 Perovskite Nanocrystals

“…Halide perovskites have garnered significant attention and extensive research as compelling candidates for optoelectronic applications. It is primarily due to their remarkable properties, including a high absorption coefficient, impressive luminescence efficiency, and long carrier diffusion lengths. − These optical and electrical properties can be effectively tuned by changing their chemical composition. − As the chemical composition directly influences the dimensionality of perovskites, low-dimensional structures are easy to obtain by altering metal cations, mixing halide ions, and using long chain organic ligands. In low dimensional metal-halides, the strong lattice distortion induced by the pseudo-Jahn–Teller effect can enhance the electron–phonon interactions. − Furthermore, since the charge carriers (excitons) are well confined, the exciton binding energy is large, leading to an efficient exciton radiative recombination and high photoluminescence quantum yield (PLQY).…”