The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters

Abstract

The electroluminescence quantum efficiency roll-off in iridium(III)-based complexes, namely Ir(iqbt) 2 (dpm) and Ir(iqbt) 3 (iqbt = 1 (benzo[b]thiophen-2-yl)-isoquinolinate, dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) utilized as near-infrared emitters in organic light emitting diodes with remarkable external quantum efficiencies, up to circa 3%, 1.5% and 1%, are measured and analyzed. With a 5-6 weight% of emitters embedded in a host matrix, the double-layer solution-processed structure as well as analogous three-layer one extended by a hole-conducting film are investigated. The triplet-polaron, the Onsager electron-hole pair dissociation and the triplet-triplet annihilation approaches were used to reproduce the experimental data. The mutual annihilation of triplets in iridium emitters was identified as prevailingly controlling the moderate roll-off, with the interaction between those of iridium emitters and host matrixes found as being less probable. Following the fitting procedure, the relevant rate constant was estimated to be (0.5 − 12) × 10 −12 cm 3 /s, values considered to be rather too high for disordered organic systems, which was assigned to the simplicity of the applied model. A coexistence of some other mechanisms is therefore inferred, ones, however, with a less significant contribution to the overall emission quenching.

Rational Design of Ir(III) Phosphors to Strategically Manage Charge Recombination for High-Performance White Organic Light-Emitting Diodes

“…Because of the favorable merits of sun-like light, low blue-light risk, light weight, easy flexibility, and so forth, white organic light-emitting diodes (WOLEDs) developed rapidly. − Currently, significant researches are focused on enhancing the electroluminescence (EL) performance from the perspective of device optimization and emitting materials design to meet the stringent demand toward practical commercialization. − Phosphorescence Ir­(III) complexes are highly preferred for the construction of WOLEDs among the reported emitting materials. However, serious efficiency roll-offs always appear in monochromic OLEDs and WOLEDs based on Ir­(III) complexes because of triplet–triplet exciton quenching and charge-carrier imbalance. − The roll-offs in efficiency have a negative impact on the operation lifetime and power consumption, which significantly limited the practical applications of devices employing Ir­(III) phosphors as the emitting layers. It is crucial to develop robust Ir­(III) complexes to construct high-efficiency monochromic OLEDs and WOLEDs with low roll-off.…”

Deep-Red and Near-Infrared Iridium Complexes with Fine-Tuned Emission Colors by Adjusting Trifluoromethyl Substitution on Cyclometalated Ligands Combined with Matched Ancillary Ligands for Highly Efficient Phosphorescent Organic Light-Emitting Diodes

“…Correspondingly, these phosphorescent dopants can perform certain functions related to charge transport, acting as an additional auxiliary channel in conjunction with the Bebp 2 host. This is in favor of balanced charge fluxes and broader recombination zones within the series of EMLs, effectively reducing triplet–triplet annihilation (TTA) processes, which are considered responsible for emitting state quenching, leading to unwanted EL efficiency roll-off [ 26 ]. These procedures ensure all these devices achieve, in general, high efficiency levels for deep-red and NIR emission OLEDs [ 2 , 8 , 19 ], especially under the practical luminance range of 100–1000 nit.…”