Rivers of Light—Ternary Exciplex Blends for High Efficiency Solution‐Processed Red Phosphorescent Organic Light Emitting Diodes

Abstract

Red‐emitting organic light‐emitting diodes (OLEDs) are important for displays and lighting, with the latter benefiting from solution processable materials, which would enable low embedded energy, scalable fabrication. Herein, the effect of annealing and phase separation on the performance of solution‐processed OLEDs incorporating a light‐emitting layer composed of the exciplex host, m‐MTDATA:OXD‐7, and a red phosphorescent light‐emitting dendrimer, Ir(tDCpq)3, is described. Solution‐processed OLEDs containing an annealed emissive layer with a low dendrimer concentration (2 wt%) are found to have the best performance, which is higher than the device in which the light‐emitting layer is not annealed. The improvement in the performance of the annealed device is ascribed to improved charge mobility within the emissive layer caused by phase separation of the OXD‐7. The OLEDs containing annealed m‐MTDATA:OXD‐7:(2 wt%) Ir(tDCpq)3 have maximum current, power, and external quantum efficiencies of 17.9 cd A−1, 19.4 lm W−1, and 14.8 ± 0.6%, respectively. The fact that the maximum external quantum efficiency (EQE) of 14.8% is larger than that expected based on the photoluminescence quantum yield (PLQY) and the normal out‐coupling efficiency of 20% from a bottom‐emitting device is determined to arise from the different pathways of exciton formation under photoexcitation and charge injection.

Properties of Dual Emissive Dendrimers Based on ThermallyActivated Delayed Fluorescence Dendrons and a Phosphorescent Ir(ppy)3 Core

“…Deuterated chloroform was referenced to 7.26 ppm for the 1 H NMR and 77.16 ppm for the 13 C NMR. Deuterated dichloromethane was referenced to 5.32 ppm for the 1 H NMR and 53.84 ppm for the 13 C NMR. [35] Peak multiplicities are reported as doublet (d), multiplet (m), and doublet of doublets (dd).The following symbols indicate peak assignments, CarbH = carbazolyl proton, FlH = fluorenyl proton, CarbTriPhH = proton of phenyl attached to triazine and carbazole, APhH = aminophenyl proton, PhH = phenyl proton, PhTriPhH = proton of phenyl attached to triazine and phenyl group, FPhH, = fluorophenyl proton, BrPhH, = bromophenyl proton, LH = ligand proton, PrH = propyl proton, EHH = 2-ethylhexyl proton, EPhH = proton of phenyl with a 2-ethylhexyl group attached.…”

“…NMR spectra were measured using Bruker Avance 500 MHz or Ascend 500 MHz spectrometers with chemical shifts (δ) reported in parts per million (ppm) and referenced to the residual solvent peak. Deuterated chloroform was referenced to 7.26 ppm for the 1 H NMR and 77.16 ppm for the 13 C NMR. Deuterated dichloromethane was referenced to 5.32 ppm for the 1 H NMR and 53.84 ppm for the 13 C NMR.…”

“…1 H NMR (500 MHz, CD 2 Cl 2 ): δ H 7.27-7.31 (4H, m, FPhH), 7.75 and 8.65 (4H, AA′BB′, BrPhH), 8.78-8.82 (4H, m, FPhH). 13 C NMR (126 MHz, CD 2 Cl 2 ): δ C 115.8 (J = 22 Hz), 127.6, 130.5, 131.3 (J = 9.0 Hz), 132.0, 132.2 (J = 3.0 Hz), 135.1, 165.0, 167.0, 170.9 (J = 14 Hz). HRMS (ESI-Orbitrap) for C 21 H 12 BrF 2 N 3 m/z: [M+H] + Calcd: 424.0255 (100%), 425.0289 (23%), 426.0235 (98%), and 427.0268 (22%).…”

“…Advanced Functional Materials published by Wiley-VCH GmbH 2.0 Hz, CarbH), 7.94 and 9.00 (4H, AA′BB′, PhTriPhH), 8.01 and 9.20 (8H, AA′BB′, CarbTriPhH), 8.61 (4H, d, J = 1.5 Hz, CarbH). 13…”

“…[ 12 ] However, the two components in an exciplex host may not always form blends of optimal morphology for charge transport and/or exciton formation when mixed with the emissive material. [ 13 ] TADF emitters are essentially covalently linked exciplex blends and have been used as host materials in conjunction with phosphorescent emitters to give efficient OLEDs. [ 14 ] We were therefore interested to investigate the effect of connecting TADF‐based dendrons on the properties of light‐emitting dendrimers with a phosphorescent iridium(III) complex at the core.…”