Tracking thermal transport in colloidal quantum dot films using in-situ time-resolved X-ray diffraction

TL;DR

This paper introduces a contact-free, time-resolved X-ray diffraction method to measure the thermal response of colloidal quantum dots in situ, revealing their low thermal conductivity and interfacial conductance in device-like environments.

Contribution

It demonstrates a novel application of in-situ time-resolved X-ray diffraction to directly measure thermal properties of quantum dot films and dispersions.

Findings

Thermal conductivity of QD thin-films is as low as 0.55 W/m·K.

Interfacial thermal conductance in QD dispersions is approximately 15 MW/m²·K.

The method captures heating and cooling dynamics on a sub-nanosecond timescale.

Abstract

Colloidal quantum dots (QDs) and their thin-films are increasingly used in electronic and photonic devices replacing traditional bulk semiconductors. However, thermal properties of the QDs are comparatively underexplored relative to device development efforts. This study shows the use of time-resolved X-ray diffraction as a contact-free method to probe the thermal response of QDs in device-like environments, providing in-situ insights for future thermal management strategies. Through the extraction of Debye-Waller Factors on a sub-nanosecond timescale, we use time-resolved X-ray diffraction to directly capture the heating and cooling of core/shell CdSe/CdS QDs following pulsed optical excitation. In a QD thin-film that actively provides optical gain, the thermal conductivity is found to be as low as 0.55 $\mathrm{W\,m^{-1}\,K^{-1}}$, because of the poor heat flow within close-packed QD solids. For QDs dispersed in liquids, interfacial thermal conductance is found to dominate the thermal relaxation with a conductance on the order of 15 $\mathrm{MW\,m^{-2}\,K^{-1}}$.