Transport properties of annealed CdSe nanocrystal solids

TL;DR

This study investigates how annealing affects the electrical transport, optical properties, and microscopic structure of CdSe nanocrystal solids, revealing enhanced conductivity and subtle spectral shifts due to reduced inter-dot separation and chemical changes.

Contribution

It provides new insights into how annealing modifies the transport and optical properties of CdSe nanocrystal assemblies through structural and chemical alterations.

Findings

Annealing significantly increases dark and photocurrent in CdSe NC solids.

Inter-dot separation decreases after annealing, enhancing tunneling.

Spectral shifts suggest changes in dielectric environment and Coulomb interactions.

Abstract

Transport properties of artificial solids composed of colloidal CdSe nanocrystals (NCs) are studied from 6 K to 250 K, before and after annealing. Annealing results in greatly enhanced dark and photocurrent in NC solids, while transmission electron microscopy (TEM) micrographs show that the inter-dot separation decreases. The increased current can be attributed to the enhancement of inter-dot tunneling caused by the decreased separation between NCs and by chemical changes in their organic cap. In addition, the absorption spectra of annealed solids are slightly red-shifted and broadened. These red-shifts may result from the change of the dielectric environment around the NCs. Our measurements also indicate that Coulomb interactions between charges on neighboring NCs play an important role in the tunneling current.