Construction of High‐Quality Cu(I) Complex‐Based WOLEDs with Dual Emissive Layers Achieved by an “On‐and‐Off” Deposition Strategy

Abstract

for their wide range of commercial applications including energy-efficient solidstate lighting, backlights for liquid-crystal displays (LCDs), and full-color OLEDs. [1] Nevertheless, in comparison with their commercial competitor white lightemitting diodes (WLEDs), which are based on inorganic materials, there are still urgent challenges for WOLEDs to further simplify device structures, lower costs, and improve the quality of white light.Generally, white emission light can be achieved through either the combination of two complementary colors or three primary colors (RGB), where the former strategy features in simpler structure but is hard to satisfy daily lighting due to relatively low color-rendering index (CRI) while the latter one leads to better CRI but requires multiple emissive layers (EMLs) in devices. Moreover, the cost for high-efficiency WOLEDs is significantly increased by introducing phosphorescent materials. The utilization of precious metal complexes (e.g., iridium, platinum, and osmium) ensures to harness the energies of both the singlet and triplet excitons to give internal quantum efficiencies of 100% [2] but sets great obstacles for future commercialization due to their low abundance and unclear toxicity.With the aim of surmounting the challenges above, Cu(I) complexes provide potential alternatives for a realistic approach to low-cost and high-efficiency devices due to their excellent photoluminescence, color-tuning features, and eco-friendliness. Till now, intensive research has been conducted in OLEDs based on Cu(I) complexes which can be comparable to that of iridium complex OLEDs. [3] Despite high-profile progress in green emissive OLEDs, it remains challenging to design efficient orange or red Cu(I) complexes, which play a key role to achieve white light. More importantly, tradition methods for OLEDs fabrication (e.g., vacuum deposition or spin coating) cannot be applied to most emissive Cu(I) complexes due to their instability during sublimation and poor solubility in common solvents. To expand the use of Cu(I) emissive complexes and simplify device fabrication in OLEDs, we have demonstrated a codeposition (CD) method to make Cu(I) complexes as emitters for OLEDs. [4] This method involves codeposition of CuI and a nitrogen-coordinating ligand/host compound to form a Cu(I) complex-doped EML in situ, where the ligand Inexpensive and highly luminescent Cu(I) complexes exhibit great potential as emitters in organic light-emitting diodes (OLEDs), especially in white OLEDs (WOLEDs). In this work, two compounds 9-(3-(quinolin-4-yl)phenyl)-9H-carbazole (CzPQ) and 9,9′-(quinoline-4,6-diylbis(3,1-phenylene))bis(9Hcarbazole) (2CzPQ) are designed and synthesized to form Cu(I) complexes in situ by codeposition with copper iodide (CuI). The corresponding OLEDs show an orange red emission with a maximum external quantum efficiency (EQE) of 6.7%. Based on this result, an "on-and-off " strategy is proposed to achieve WOLEDs with the combination of Cu(I) complex layer and the pure ligand layer by contr...

Regulation strategy of white emission from organic–inorganic hybrid metal halide perovskites

“…), organic (including small molecules and polymers), [20][21][22][23] and organic-inorganic hybrid materials (such as metal-organic frameworks, semiconductors, and metal complexes etc.). [24][25][26][27] However, the inorganic materials and organic small molecules have some problems, such as complex synthesis and difficult processing, while polymers have poor repeatability and rela-tively low luminescence efficiency. Organic-inorganic hybrid materials, which combine the advantages of inorganic and organic WLEMs, are expected to overcome the above problems, showing great potential in the field of WLEDs.…”

Excellent Blue Emissive Neutral Cu(I) Complexes: Structural Analysis, Thermochromic Luminescent Properties, and Terahertz Spectrum Research

“…Recently, Cu­(I)-based complexes have been widely studied in luminescent materials, such as fluorescent probes, chemical sensors, bioimaging agents, and organic light-emitting diodes (OLEDs). − Not only their fantastic photophysical properties but also their relatively inexpensive cost, low toxicity, and rich abundance in earth make Cu­(I) ions a potential alternative for traditional noble metals such as iridium and platinum . Due to the effects of heavy atom effects, many Cu­(I) complexes have pure phosphorescent emission, and the others exhibit typical thermally activated delayed fluorescence (TADF) characteristics. ,− Thus, the theoretical value of internal quantum efficiency can easily reach 100%. − Benefitting from the above advantages, many devices of Cu­(I) complexes have been synthesized in recent years, and their luminescent color covers the whole visible region. − …”

Low-Voltage Driving Copper Iodide-Based Broadband Electroluminescence

“…It is known that Cu­(I) complexes can be efficient light-emitting materials with broadband emission − and some Cu­(I) complex-based LEDs are considered WLEDs (Table ). − One important emissive Cu­(I) complex is the copper iodide complex, which can be feasibly synthesized by CuI and some pyridine-based organic ligands. − In the typical cesium copper iodide-based LEDs, the organic electron-transporting layers (ETLs), which commonly contain pyridine groups, are evaporated directly on the cesium copper iodide films. Cesium copper iodides are low-dimensional materials with edge-sharing [CuI 4 ] 3– or [Cu 2 I 5 ] 3– separated by Cs + atoms .…”