Unraveling the Interplay between Structure and Photophysics in Colloidal Quantum Dot Nanostructures

Abstract

Colloidal quantum dots (QDs) make up a class of nanomaterials that provide a remarkable platform for engineering photophysical properties tailored to a range of applications of considerable technological value, including energy-efficient LEDs, robust biological probes, low-threshold solution-processed lasers, advanced photocatalysts and single-photon sources for quantum technologies. Underpinning these uses of QDs lay more fundamental investigations into the role of structure on absorption, energy relaxation, charge separation and charge recombination in order to achieve complete control over their photophysical behavior. However, with complex interfaces and diverging morphologies in synthetic products, QDs are remarkably complex nanostructured materials. It is therefore challenging to develop detailed structure-function relationships at the ensemble scale—where the properties of an array of structures are simultaneously determined. To decode this information, it is necessary to study QD nanostructures one at a time. In this work, single QD investigations were applied to three different QD systems to better understand the interplay between structure and photophysics in these materials. From revealing the role of strain-induced structural changes on the color purity of CdSe-CdS core-shell QDs, to a thick-shell in suppressing random intermittent emission in cadmium-free InP QD nanostructures, these investigations continually point to the negative impact of structural heterogeneity on the properties of the ensemble. The implementation of a correlative technique to measure the structure and photophysics of the same QD facilitated a detailed examination of this heterogeneity in semiconductor nanorods—revealing the detrimental effects of surface roughness on the quantum efficiency of the material. The advanced characterization of QDs afforded by this technique also has far-reaching implications for QD development and could be used to inform methods to orchestrate the assembly of QD nanostructures with precisely tuned photophysical properties.