Anomalous phase transitions in one-dimensional organo-metal halide perovskite nanorods grown inside porous silicon nanotube templates

TL;DR

This study investigates how one-dimensional organo-metal halide perovskite nanorods grown inside porous silicon nanotubes exhibit inhibited phase transitions compared to bulk perovskites, due to surface stress effects, affecting their low-temperature properties.

Contribution

It demonstrates that nanoscale confinement and surface stress inhibit the structural phase transition in perovskite nanorods, unlike bulk materials, providing insights into their phase stability and optical properties.

Findings

Bulk perovskites transition from tetragonal to orthorhombic at 150K.

Nanorods remain tetragonal down to 4K, inhibiting phase transition.

Surface stress from high surface area prevents orthorhombic phase formation.

Abstract

One-dimensional organo-metal halide Perovskite (CH3NH3PbI3) nanorods whose diameter and length are dictated by the inner size of porous silicon nanotube templates have been grown, characterized and compared to bulk perovskites in the form of microwires. We have observed a structural phase transition for bulk perovskites, where the crystal structure changes from tetragonal to orthorhombic at about 150K, as opposed to small diameter one-dimensional perovskite nanorods, of the order of 30-70 nm in diameter, where the phase transition is inhibited and the dominant phase remains tetragonal. Two major experimental techniques, infrared absorption spectroscopy and photoluminescence, were utilized to probe the temperature dependence of the perovskite phases over the 4-300K temperature range. Yet, different characteristics of the phase transition were measured by the two spectroscopic methods and explained by the presence of small, tetragonal inclusions embedded in the orthorhombic phase. The inhibition of the phase transition is attributed to the large surface area of these one-dimensional perovskite nanorods, which gives rise to a large stress that, in turn, prevents the formation of the orthorhombic phase. The absence of phase transition enables the measurement of the tetragonal bandgap energy down to low temperatures.