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

While crystalline 2D metal halide perovskites (MHPs)representa well-celebrated semiconductor class, supporting applications inthe fields of photovoltaics, emitters, and sensors, the recent discoveryof glass formation in an MHP opens many new opportunities associatedwith reversible glass-crystalline switching, with each state offeringdistinct optoelectronic properties. However, the previously reported[S-(-)-1-(1-naphthyl)ethyl-ammonium](2)PbBr4 perovskite is a strong glass former withsluggish glass-crystal transformation time scales, pointing to a needfor glassy MHPs with a broader range of compositions and crystallizationkinetics. Herein we report glass formation for low-melting-temperature1-MeHa(2)PbI(4) (1-MeHa = 1-methyl-hexylammonium)using ultrafast calorimetry, thereby extending the range of MHP glassformation across a broader range of organic (fused ring to branchedaliphatic) and halide (bromide to iodide) compositions. The importanceof a slight loss of organic and hydrogen iodide components from theMHP in stabilizing the glassy state is elucidated. Furthermore, theunderlying kinetics of glass-crystal transformation, including activationenergies, crystal growth rate, Angell plot, and fragility index, isstudied using a combination of kinetic, thermodynamic, and rheologicalmodeling techniques. An inferred fast crystal growth rate of 0.21m/s for 1-MeHa(2)PbI(4) shows promise toward suitabilityin extended application spaces, for example, in metamaterials, nonvolatilememory, and optical and neuromorphic computing devices.

Automated summary

This study reports the glass formation and kinetic properties of low-melting-temperature 1-MeHa(2)PbI(4) perovskite. The slight loss of organic and hydrogen iodide components helps stabilize the glassy state, and the fast crystal growth rate shows potential for extended applications.