Efficient Vacuum‐Processed Light‐Emitting Diodes Based on Carbene–Metal–Amides

Abstract

Efficient vacuum-processed organic light-emitting diodes are fabricated using a carbene-metal-amide material, CMA1. An electroluminescence (EL) external quantum efficiency of 23% is achieved in a host-free emissive layer comprising pure CMA1. Furthermore external quantum efficiencies of up to 26.9% are achieved in host-guest emissive layers. EL spectra are found to depend on both the emissive-layer doping concentration and the choice of host material, enabling tuning of emission color from mid-green (Commission Internationale de l'Éclairage co-ordinates [0.24, 0.46]) to sky blue ([0.22 0.35]) without changing dopant. This tuning is achieved without compromising luminescence efficiency (>80%) while maintaining a short radiative lifetime of triplets (<1 μs).

Environmental Control of Triplet Emission in Donor–Bridge–Acceptor Organometallics

“…We have previously reported efficient CMA1:PVK solution‐processed OLEDs, using a CMA1 concentration of 20% by weight . Figure a presents the steady‐state absorption and photoluminescence spectra of CMA1 doped in to PVK host at concentrations from 100% (neat CMA1) to 5% by weight, representing the range of dopant concentrations over which efficient OLED devices have been shown to be achievable . The absorption of CMA1 in PVK is dominated by parasitic host absorption and a weak scattering tail, which obscures the exact CMA1 absorption edge.…”

Highly efficient blue organic light-emitting diodes based on carbene-metal-amides

“…19 These complexes are soluble in most organic solvents and sufficiently thermally stable to enable the fabrication of OLED devices by both solution processing and thermal vapour deposition techniques. 13, [19][20][21] CMAs do not suffer from strong concentration quenching in the solid state, attributed to the lack of close metal-metal contacts, enabling the realization of host-free green devices with an external quantum efficiency (EQE) of 23.1%. 20 Due to the linear two-coordinate geometry, CMAs are conformationally flexible, with a low barrier for rotation about the metal-N σ-bond.…”

“…13, [19][20][21] CMAs do not suffer from strong concentration quenching in the solid state, attributed to the lack of close metal-metal contacts, enabling the realization of host-free green devices with an external quantum efficiency (EQE) of 23.1%. 20 Due to the linear two-coordinate geometry, CMAs are conformationally flexible, with a low barrier for rotation about the metal-N σ-bond. The highest occupied molecular orbital (HOMO) is centred on the amide ligand while the lowest unoccupied molecular orbital (LUMO) consists mainly of the p-orbital of the carbene C atom, with only a small metal contribution to both.…”

“…As a consequence of the high polarity of CMA emitters, emission energies are sensitive to their molecular environment; for example, this has allowed "tuning" of electroluminescence by suitable host media from green to sky-blue. 20 However, much larger changes in emission energies can be achieved by altering the carbazole substitution pattern. For the ( Ad CAAC)AuCz archetype, the HOMO is almost entirely located on the Cz donor.…”

Thermally Stable Donor–Acceptor Type (Alkynyl)Gold(III) TADF Emitters Achieved EQEs and Luminance of up to 23.4% and 70 300 cd m−2 in Vacuum‐Deposited OLEDs

“…The first example of gold OLED was reported by Ma and Che in 1999 [1,2] with inferior performance, and device performance has been improved in recent years exploiting luminescent cyclometalated Au(III) complexes. Recently, we and Linnolahti, Bochmann, Credgington and coworkers independently reported strongly luminescent Au(III) and Au(I) TADF emitters, [21][22][23] respectively, and successfully use these emitters in the fabrication of high performance gold OLEDs with external quantum efficiencies (EQEs) up to 23.8% and 27.5%, and efficiency roll-off down to 1% and 4%, respectively. A relatively short triplet emission lifetime is not only important to suppress efficiency roll-off but also crucial to achieve stable device with long operation lifetimes.…”