Pressure‐Induced Metallization of Lead‐Free Halide Double Perovskite (NH₄)₂PtI₆

Abstract

Metallization has recently garnered significant interest due to its ability to greatly facilitate chemical reactions and dramatically change the properties of materials. Materials displaying metallization under low pressure are highly desired for understanding their potential properties. In this work, the effects of the pressure on the structural and electronic properties of lead-free halide double perovskite (NH 4 ) 2 PtI 6 are investigated systematically. Remarkably, an unprecedented bandgap narrowing down to the Shockley-Queisser limit is observed at a very low pressure of 0.12 GPa, showing great promise in optoelectronic applications. More interestingly, the metallization of (NH 4 ) 2 PtI 6 is initiated at 14.2 GPa, the lowest metallization pressure ever reported in halide perovskites, which is related to the continuous increase in the overlap between the valence and conduction band of I 5p orbital. Its structural evolution upon compression before the metallic transition is also tracked, from cubic Fm-3m to tetragonal P4/mnc and then to monoclinic C2/c phase, which is mainly associated with the rotation and distortions within the [PtI 6 ] 2octahedra. These findings represent a significant step toward revealing the structure-property relationships of (NH 4 ) 2 PtI 6 , and also prove that high-pressure technique is an efficient tool to design and realize superior optoelectronic materials.

Nanoscale Thermal Strain Engineering-Driven Ferroelastic Domain Evolution in CH3NH3PbI3 Perovskites

“…Such short rod-like domain patterns cannot be seen in previous studies, which usually demonstrated band-like domain patterns in MAPbI 3 crystals and thin films imaged by polarized light optical microscopy, piezoresponse force microscopy, and PTIR approach. 7,8,[11][12][13]23,24 To understand further such unique domain configurations, the chemical image in Figure 3b is simultaneously obtained by IR laser illuminating the sample at 1468 cm −1 , which corresponds to the CH 3 asymmetric deformation of the methylammonium ions (MA + ). 42 Different contrasts in Figure 3b arise from the local photothermal expanding contribution of local chemical structures in response to the IR illumination, for which contrasts reflect diverse local IR energy absorption of MA + and thus also reflects local MA + concentration.…”

“…Metal halide perovskites (MHPs) have been paid significant attention due to their most promising applications in next-generation solar cells. − The power conversion efficiency of MHP solar cells has been increased from the initial 3.9% in 2009 to 25.7% in 2022. , Such a unique performance is closely involved with their microstructures and the corresponding dynamics in response to external fields. − For tetragonal methylammonium lead triiodide perovskites (MAPbI 3 ) at room temperature, their ferroic microstructures have been considered to be ferroelectric domains, − ferroelastic domains, ,, and domains with alternating polar and non-polar orders in recent studies. , These interesting features reveal the microstructural complexities in the MAPbI 3 system. In view of space group of tetragonal MAPbI 3 at room temperature, both the proposed polar I 4 cm or non-polar I 4/ mcm group could give rise to ferroelastic domains with 0, 45, and 90° domain walls for MAPI 3 crystals and predominant 70 and 90° walls for MAPbI 3 thin films .…”

Theoretical and Experimental Advances in High-Pressure Behaviors of Nanoparticles

“…In the past decade, perovskite materials, especially MHPs, have attracted significant attention as they offer tremendous possibilities in energy-related applications, such as photovoltaic cells, light emitting diodes, and lasers. − As discussed in the previous sections, high-pressure technology is a powerful and clean tool used to adjust the physical and chemical properties of various functional nanomaterials. In recent years, high-pressure research has also been conducted on perovskite-based materials to optimize their physicochemical characteristics and to induce emission enhancement, − band gap optimization, − lifetime prolongation, − piezochromism, − and metallization. − In addition, a new concept of PIE has been proposed based on the novel phenomenon where pressure is used to induce emission in various nonluminescent perovskite materials. − Pressure tunable structures with their associated optoelectronic properties show great potential to extend the perovskite application space. While there have been excellent review articles and perspectives published on the high-pressure behavior of bulk perovskite materials, − high-pressure-induced transformations in perovskite NCs have been summarized less frequently. , In this section, we offer an overview of recent research discoveries on high-pressure behaviors of perovskite NCs, with a focus on pressure- induced structure and optoelectronic property changes.…”

Chirality-Dependent Structural Transformation in Chiral 2D Perovskites under High Pressure

“…Hydrostatic pressure, as a physical parameter independent of chemical composition and temperature, is regarded as a powerful and clean tool to study the structure–property relationships of materials that cannot be revealed under ambient conditions. − The application of high-pressure on achiral OIHPs has achieved bandgap tunability, − enhanced photocurrent, improved emission performance, − and prolonged carrier lifetime. − Nevertheless, the evolution of the crystal structures and properties for chiral OIHPs under high pressure remains unexploited. Owing to unique asymmetric hydrogen bonding interactions between chiral organic ammoniums and achiral inorganic frameworks, pressure-driven structural evolution and optical behavior in chiral OIHPs are expected to be significantly different from the pressure effects in achiral OIHPs.…”