Electrochemically-stable ligands bridge photoluminescence-electroluminescence gap of quantum dots

TL;DR

This paper identifies electrochemical reactions of ligands as a degradation channel in QLEDs and introduces electrochemically-inert ligands to significantly improve their efficiency and operational lifetime.

Contribution

It reveals a previously overlooked degradation mechanism and proposes a ligand engineering strategy to enhance QLED performance and longevity.

Findings

Record-long operational lifetimes for red and blue QLEDs.

Electrochemically-inert ligands effectively bridge the photoluminescence-electroluminescence gap.

The strategy is general for improving QLED stability and efficiency.

Abstract

Colloidal quantum dots (QDs) are promising emitters for electroluminescence devices (QD light-emitting-diodes, QLEDs). Though QDs have been synthesized with efficient and stable photoluminescence, inheriting their superior luminescence in QLEDs remains challenging. This is commonly attributed to unbalanced charge injection and/or interfacial exciton quenching in the devices, instead of lack of suited QD materials. Here, a general but previously overlooked degradation channel in QLEDs, i.e., operando electrochemical reactions of surface ligands with injected charge carriers, is identified after systematic studies of various combination of core/shell QDs and ligands. Applying electrochemically-inert ligands to highly photoluminescent QDs is developed to bridge their photoluminescence-electroluminescence gap. This material-design principle is general for boosting electroluminescence efficiency and lifetime of the QLEDs, resulting in record-long operational lifetimes for both red-emitting QLEDs (T95 > 3800 hours at 1000 cd m-2) and blue-emitting QLEDs (T50 >10,000 hours at 100 cd m-2). Our study provides a critical guideline for the QDs to be used in optoelectronic and electronic devices.