Lattice Dynamics and Thermal Stability of Cubic-Phase CsPbI₃ Quantum Dots

Abstract

Cubic-phase CsPbI quantum dots (QDs) have been recently synthesized with merits of excellent optoelectronic performance. However, vital properties of cubic CsPbI including lattice dynamics and stability at high temperature remain poorly explored. We fabricate cubic CsPbI QDs and study their lattice dynamic and thermal stability to 700 K. We obtain Raman modes of cubic CsPbI QDs from 300 to 500 K at ultra-low-frequency range down to 15 cm, consistent with first-principles calculations. Above 550 K, the modification of Raman features suggests sample degradation. Consistently, temperature-dependent photoluminescence measurements indicate the absence of other luminescence phases up to 700 K. With increasing temperature, the CsPbI QD photoluminescence peak has a blue shift with exponentially decreasing intensity, showing faster electronic degradation than structural degradation. Our work provides detailed investigation of CsPbI QD lattice dynamics, band gap, and their high-temperature behavior, potentially useful for their emerging optoelectronic applications.

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“…S2). Simultaneously, Raman spectroscopy (see Materials and Methods) confirms the presence of lead iodine octahedra with the characteristic peak at around 100 cm −1 seen for most lead iodide perovskites (25,26), as shown in fig. S3 (see Materials and Methods for further details on the synthesis and spectroscopic measurements).…”

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“…Work has been done on identifying phase transition using temperature-dependent Raman spectra on perovskites quantum dots, 55,56 where the Raman shift was slightly different to the bulk. We believe future experimental studies of size-dependent Raman spectra in perovskites quantum dots will help validate the behaviour we predict in this work.…”

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“…(b) Raman spectra of CsPbI 3 QDs at temperatures ranging from 300 to 700 K. The arrow indicates the variation in temperature. Reprinted from ref . Copyright 2018 American Chemical Society.…”