Study of Glass Formation and Crystallization Kinetics in a 2D Metal Halide Perovskite Using Ultrafast Calorimetry

Abstract

While crystalline 2D metal halide perovskites (MHPs) represent a well-celebrated semiconductor class, supporting applications in the fields of photovoltaics, emitters, and sensors, the recent discovery of glass formation in an MHP opens many new opportunities associated with reversible glass-crystalline switching, with each state offering distinct optoelectronic properties. However, the previously reported [S-(−)-1-(1-naphthyl)ethylammonium] 2 PbBr 4 perovskite is a strong glass former with sluggish glass-crystal transformation time scales, pointing to a need for glassy MHPs with a broader range of compositions and crystallization kinetics. Herein we report glass formation for low-melting-temperature 1-MeHa 2 PbI 4 (1-MeHa = 1-methyl-hexylammonium) using ultrafast calorimetry, thereby extending the range of MHP glass formation across a broader range of organic (fused ring to branched aliphatic) and halide (bromide to iodide) compositions. The importance of a slight loss of organic and hydrogen iodide components from the MHP in stabilizing the glassy state is elucidated. Furthermore, the underlying kinetics of glass-crystal transformation, including activation energies, crystal growth rate, Angell plot, and fragility index, is studied using a combination of kinetic, thermodynamic, and rheological modeling techniques. An inferred fast crystal growth rate of 0.21 m/s for 1-MeHa 2 PbI 4 shows promise toward suitability in extended application spaces, for example, in metamaterials, nonvolatile memory, and optical and neuromorphic computing devices.

Rational Design of 2D Metal Halide Perovskites with Low Congruent Melting Temperature and Large Melt-Processable Window

“…Commonly, the 2D MHPs with noniodided alkylammoniums tend to undergo rapid crystallization upon cooling, which demands an ultrafast critical cooling rate (CCR) for vitrification, while the melts of (MIPA) 2 PbI 4 or (DMIPA) 2 PbI 4 can vitrify at a low CCR (<40 °C/min) (Figure b and Figure S15). This observation indicates a higher viscosity in iodo-substituted MHPs compared to with nonsubstituted counterparts . The experimentally measured viscosity at around T m for (MIPA) 2 PbI 4 is consistent with expectation (Figure S16), and the viscosity value is larger than that of 1-MeHa 2 PbI 4 (1-MeHa = 1-methyl-hexylammonium), which provide additional evidence for the presence of I···I interactions in molten systems.…”

“…The CCR, indicative of the liquid’s vitrification potential, is approximately 40 °C/min as determined from the DSC scans (Figure b). This rate is notably slower than those of common MHP glasses, underscoring its enhanced propensity for glass formation. By employing the crystallization peak values derived from the heating curves, we computed the approximate activation energy ( E A ) linked with the glass crystallization to be 74.27 ± 3.13 kJ/mol by utilizing the widely accepted Kissinger model (Figure S23).…”

“…The phenomenon of congruent melting, that is, melting without undergoing decomposition, presents a myriad of opportunities. For example, melt processing does not need toxic solvents, allows for potential crystal orientation control using temperature gradients, and enables self-encapsulation in a single step without requiring external adhesives, showing advantages over conventional spin coating methods for film preparation. , It opens avenues for high-throughput techniques like roll-to-roll processing, lamination, capillary filling, and extrusion methods. − The molten state also provides a unique platform for synthesizing novel phases or introducing dopants to tailor functionalities. , Moreover, the 2D MHPs with congruent melting fulfill prerequisites for glass formation via melt quenching, potentially leading to the creation of MHP glasses and opening avenues for materials engineering in diverse optoelectronic applications. − …”

Dopant effect on the optical and thermal properties of the 2D organic–inorganic hybrid perovskite (HDA)2PbBr4

“…Otherwise, the phase transition temperature is critical for solvent-free device fabrication in 2D HOIPs. Though the organic cation effect on the phase transition of 2D HOIPs is well studied, 24,25 the dopant ion effect is rarely studied.…”

Photoluminescence Switching and Non-Volatile Memory in Hybrid Metal-Halide Phase-Change Materials

“…The viscosity values measured around T m are approximately 3.1 times greater than the one of (1-MeHa) 2 PbI 4 (1-MeHa = 1-methyl-hexylammonium) (Figure S6). As a comparison, bulky and rigid organic cations are usually incorporated into the HMHs to tend to form a glassy state due to high spatial resistance, which can diminish crystallization trends during cooling . Here, the rich intermolecular interactions in 1 S afford a complementary strategy to avoid crystallization of the melt and increase the possibility of glass formation in the HMHs.…”