Colloidal CdSe_1–xS_x Nanoplatelets with Narrow and Continuously-Tunable Electroluminescence

Abstract

Colloidal nanoplatelets, quasi-two-dimensional quantum wells, have recently been introduced as colloidal semiconductor materials with the narrowest known photoluminescence line width (∼10 nm). Unfortunately, these materials have not been shown to have continuously tunable emission but rather emit at discrete wavelengths that depend strictly on atomic-layer thickness. Herein, we report a new synthesis approach that overcomes this issue: by alloying CdSe colloidal nanoplatelets with CdS, we finely tune the emission spectrum while still leveraging atomic-scale thickness control. We proceed to demonstrate light-emitting diodes with sub-bandgap turn-on voltages (2.1 V for a device emitting at 2.4 eV) and the narrowest electroluminescence spectrum (FWHM ∼12.5 nm) reported for colloidal semiconductor LEDs.

Emergence of Nanoplatelet Light-Emitting Diodes

“…To address this issue, Fan et al finely tuned the emission spectra but leveraged atomic-scale thicknesses control by alloying CdSe colloidal NPLs with CdS [36]. As a result, the emissions could cover from green to blue transition regime (513–481 nm) via CdS-alloying of 6 monolayer CdSe NPLs.…”

“…Right: AFM for only ZnO (the surface roughness is 1.74 nm). Adapted from [36], with permission from © 2015 American Chemical Society.…”

“…Thus, NPLs are considered to be a novel family of 2D solution-processed nanocrystals for various optoelectronic applications, including solar cells, lasers and light-emitting diodes (LEDs) [34]. For NPL-LEDs, they have great potential to lighting and displays since NPL-LEDs show a plenty of outstanding characteristics, such as excellent color purity, light weight, high efficiency as well as the compatibility to flexible substrates [35,36,37]. …”

Colloidal nanocrystals for quality lighting and displays: milestones and recent developments

“…A red-shift of 8 nm was observed compared with the photoluminescence peak, which was attributed to the QCSE. Later, Fan et al reported an electroluminescent LED with emission bandwidths as narrow as 12.5 nm [84]. In this work, the emission spectra of the NPLs were controlled by tuning the Se/S ratio within alloyed NPLs in the range of 481-513 nm.…”

Assembling Ordered Nanorod Superstructures and Their Application as Microcavity Lasers

“…More recently, we have achieved strong PL emission in the cadmium chalcogenides system without a core-shell structure by combining the metal cation with both chalcogen anions in an alloy20. This alloyed nanostructure allows precise tuning of the bandgap as a function of anion ratios allowing for optimization as needed for light emitting applications2122.…”