# Ultra-Low Efficiency Roll-Off High Color Purity Blue Perovskite Quantum Dot LEDs with Exceeding 20% Efficiency

## TL;DR

Researchers developed blue perovskite QLEDs with high color purity and over 20% efficiency, even at high brightness, using a new molecule to reduce efficiency loss.

## Contribution

A multifunctional molecule passivation strategy using EMIMPF₆ to reduce efficiency roll-off in blue perovskite QLEDs.

## Key findings

- The treatment increased photoluminescence quantum yield from 78% to 92%.
- Devices achieved over 20% external quantum efficiency at 6441 cd/m² with minimal roll-off.
- Operational lifetime improved by an order of magnitude compared to previous reports.

## Abstract

Blue perovskite quantum dot light-emitting diodes (QLEDs) are highly attractive for new generation high-definition displays, but their practical deployment is hindered by severe efficiency roll-off at high brightness (>4000 cd m−²) while maintaining high color purity (CIEy < 0.1). This roll-off arises mainly from non-radiative losses induced by exposed dangling bonds, strong inter-dot coupling, and low permittivity. To conquer this challenge, we develop a multifunctional molecule passivation strategy utilizing 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆). The [PF₆]− anions coordinate with lead dangling bonds, cesium sites, and weaken coupling, while [EMIM]⁺ cations suppress bromine-related defects and inhibit Auger recombination, collectively reducing exciton quenching pathways. This treatment increases the photoluminescence quantum yield of QD films from 78% to 92% and enables spectrally high color purity blue emission at 472 nm (CIEy = 0.091). Crucially, the resulting devices deliver a record-high external quantum efficiency (EQE) exceeding 20% at 6441 cd m−² and maintain 18.47% EQE at 9587 cd m−² with nearly eliminated roll-off, representing the best performance to date for blue perovskite QLEDs (CIEy < 0.1). Moreover, the operational lifetime improves by an order of magnitude compared with previous reports.

This work achieves the high color purity blue CsPbBr3 QLEDs with ultra-low efficiency roll-off using a multifunctional molecule—EMIMPF6.