# Singlet and triplet harvesting enable efficient NIR-II quantum-dot electroluminescence

## TL;DR

A new chemical strategy boosts the efficiency of near-infrared light-emitting diodes using quantum dots and energy transfer from fluorophores.

## Contribution

A novel chemical strategy using singlet and triplet fluorophores to enhance quantum dot electroluminescence in the NIR-II range.

## Key findings

- Energy transfer from fluorophores increases photoluminescence quantum efficiency of CQDs to 85% beyond 1000 nm.
- NIR-II LEDs using this method achieve a record external quantum efficiency of 25.3% for >1000 nm emission.
- Large-area (30 mm × 30 mm) NIR-II LEDs with uniform performance demonstrate scalability of the approach.

## Abstract

Colloidal quantum dots (CQDs) are promising materials for constructing ‘second-window’ near-infrared (1000–1700 nm) light-emitting diodes (NIR-II LEDs), but their practical application has been hampered by low film external quantum efficiency (EQE). Here, we report a chemical strategy that incorporates photoactive fluorophores—spanning fluorescence, phosphorescence and thermally activated delayed fluorescence—into CQD films to boost NIR-II emission. Energy transfer from fluorophores (via both singlet and triplet pathways) raises the photoluminescence quantum efficiency of CQD to 85% beyond 1000 nm. As a result, these composite films power NIR-II LEDs with a record EQE of 25.3% for emission of >1000 nm, the highest among all LEDs with emission of >1000 nm. We further demonstrate the scalability of the approach by fabricating large-area (30 mm × 30 mm) NIR-II LEDs with uniform high performance.

Energy transfer from singlet and triplet fluorophores to quantum dots enables record-efficiency NIR-II electroluminescence, establishing a new strategy for high-performance near-infrared light-emitting devices.