Highly Efficient Blue Host-Free and Host-Guest Organic Light-Emitting Diodes Based on Carbene-Metal-Amides

TL;DR

This paper presents highly efficient, host-free blue organic light-emitting diodes using carbene-metal-amide emitters, achieving high external quantum efficiencies and stable performance at practical brightness levels.

Contribution

It introduces a new class of carbene-metal-amide emitters suitable for host-free OLEDs with record efficiencies and stable deep-blue emission.

Findings

Peak EQE of 20.9% in polar host for blue emission

Prototype host-free blue OLEDs with 17.3% EQE

Stable performance at 100 cd/m^2 brightness

Abstract

Carbene-metal-amide type photoemitters based on CF$_3$-substituted carbazolate ligands show sky-blue to deep-blue photoluminescence from charge-transfer excited states. They are suitable for incorporation into organic light-emitting diodes (OLEDs) by thermal vapour deposition techniques, either embedded within a high-triplet-energy host, or used host-free. We report high-efficiency OLEDs with emission ranging from yellow to blue (Commission Internationale de l'\'Eclairage (CIE) coordinates from [0.35, 0.53] to [0.17, 0.17]). The latter show a peak electroluminescence external quantum efficiency (EQE) of 20.9 $\%$ in a polar host. We observe that the relative energies of CT and $^{3}$LE states influence the performance of deep-blue emission from carbene-metal-amide materials. We report prototype host-free blue devices with peak external quantum efficiency of 17.3 $\%$, which maintain high performance at brightness levels of 100 cd m$^{-2}$.