Researchers from Duke University and North Carolina State University have reported glass formation for low-melting-temperature 1-MeHa2PbI4 (1-MeHa = 1-methyl-hexylammonium) using ultrafast calorimetry, thereby extending the range of metal halide perovskite (MHP) glass formation across a broader range of organic (fused ring to branched aliphatic) and halide (bromide to iodide) compositions.
A few years ago, Akash Singh and collaborators at Duke University set out to explore the realm of glassy perovskites, a departure from the traditionally studied crystalline perovskites. Since then, this topic sparked interest, resulting in the establishment of a novel research domain centered around glass-forming hybrid perovskite semiconductors with reversible switching. This recent discovery of glass formation in MHPs opens new opportunities associated with reversible glass-crystalline switching, with each state offering distinct optoelectronic properties. However, the previously reported [S-(−)-1-(1-naphthyl)ethylammonium]2PbBr4 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.
In their recent study, the researchers have demonstrated glass formation in 1-MeHa2PbI4, an exemplary MHP with lower melt viscosity that imparts enhanced crystallization kinetics. The importance of a slight loss of organic and hydrogen iodide components from the MHP in stabilizing the glassy state was studied in this work.
Furthermore, the underlying kinetics of glass-crystal transformation, including activation energies, crystal growth rate, Angell plot, and fragility index were also studied using a combination of kinetic, thermodynamic, and rheological modeling techniques.
An inferred fast crystal growth rate of 0.21 m/s for 1-MeHa2PbI4 showed promise toward suitability in extended application spaces, for example, in metamaterials, nonvolatile memory, and optical and neuromorphic computing devices.