The Root Causes of the Limited Electroluminescence Stability of Solution-Coated Versus Vacuum-Deposited Small-Molecule OLEDs: A Mini-Review

Using solution-coating methods for the fabrication of organic light-emitting devices (OLEDs) offers a tremendous opportunity for enabling low-cost products and new applications. The electroluminescence (EL) stability of solution-coated (SOL) OLEDs, however, is significantly lower than that of vacuum-deposited (VAC) OLEDs, causing their operational lifetimes to be much shorter—an issue that continues to hamper their commercialization. The root causes of the lower EL stability of these devices remain unclear. This article briefly reviews and summarizes some of the work that has been done to-date for elucidating the root cause of the lower EL stability of SOL OLEDs, giving special attention to studies where side-by-side comparisons of SOL and VAC devices of the same materials have been conducted. Such comparisons allow for more-reliable conclusions about the specific effects of the solution-coating process on device stability to be made. The mini-review is intended to introduce the work done to-date on the causes of lower stability in SOL OLEDs and to stimulate further work for the purpose of closing the existing knowledge gap in this area and surmounting this long-standing challenge in the SOL OLED technology.

All-Solution-Processed Multilayered White Polymer Light-Emitting Diodes (WPLEDs) Based on Cross-Linked [Ir(4-vb-PBI)2(acac)]

All-solution-processed multilayered white polymer light-emitting diodes (WPLEDs) are promising candidates for low-cost and large-area flexible full-color flat-panel displays and solid-state lighting. However, it is still challenging to improve their performance. In this work, based on an elegant strategy of orthogonal materials, the utilization of the cross-linked Ir³⁺ polymer film poly(NVK-co-[Ir(4-vb-PBI)₂(acac)]-co-NVK) (NVK = N-vinyl-carbazole; 4-vb-HPBI = 1-(4-vinylbenzyl)-2-phenyl-1H-benzo[d]imidazole; and Hacac = acetylacetone) as the emitting layer (EML) between a hydrophilic polymer film poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole injection layer (HIL) and a hydrophobic polymer film poly(vinyl-PBD) (vinyl-PBD = 2-(4-(tert-butyl)phenyl)-5-(4'-vinyl-[1,1'-biphenyl]-4-yl)-2,5-dihydro-1,3,4-oxadiazole) as the electron transport layer (ETL) led to the successful fabrication of reliable all-solution-processed multilayered WPLEDs. The device exhibits a η_CE^Max of 18.19 cd/A, a η_PE^Max of 8.16 lm/W, and a η_EQE^Max of 9.32% with stable white light (Commission International De L'Eclairage (CIE) coordinates x = 0.269-0.283, y = 0.317-0.330; corrected color temperatures (CCTs) of 7237-8199 K, and CRIs (color rendering indices) of 63-72) under a wide applied-voltage range. Its high performance, especially with record efficiencies among those of reported all-solution-processed WPLEDs, renders cross-linked Ir³⁺ polymers a new platform to all-solution-processed multilayered WPLEDs.

Recent progress in upconversion luminescence nanomaterials for biomedical applications

This review focuses on the biomedical applications of upconversion luminescence nanomaterials, including lanthanide-doped inorganic nanocrystals and TTA-based UCNPs.

From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes

Phosphorescent dinuclear iridium(III) complexes that can show high luminescent efficiencies and good electroluminescent abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based dinuclear iridium(III) complexes have been synthesized and fully characterized. Significant differences of the photophysical and electrochemical properties between the mono- and dinuclear complexes are observed. The theoretical calculation results show that the dinuclear complexes adopt a unique molecular orbital spatial distribution pattern, which plays the key role of determining their photophysical and electrochemical properties. More importantly, the solution-processed organic light-emitting diode (OLED) based on the new dinuclear iridium(III) complex achieves a peak external quantum efficiency (η(ext)) of 14.4%, which is the highest η(ext) for OLEDs using dinuclear iridium(III) complexes as emitters. Besides, the efficiencies of the OLED based on the dinuclear iridium(III) complex are much higher that those of the OLED based on the corresponding mononuclear iridium(III) complex.

Synthesis and electrophosphorescence of novel heteroleptic iridium complexes based on thiazole-containing ligands

Novel heteroleptic iridium complexes containing aromatic-ring-fused-thiazole in cyclometalating ligands are developed and exhibit a maximum external quantum efficiency of 22.2% in orange phosphorescent organic light-emitting diodes.

Novel bis- and tris-cyclometalated iridium(iii) complexes bearing a benzoyl group on each fluorinated 2-phenylpyridinate ligand aimed at development of blue phosphorescent materials for OLED

Novel blue phosphorescent bis- and tris-cyclometalated iridium(iii) complexes with excellent PL quantum yields were developed, using fluorinated 2-(5-benzoylphenyl)pyridinate ligands.

White light emission from a two-component hybrid gel via an energy transfer process

A two-component light-harvesting organogel containing a naphthalimide-based gelator as a donor and a phosphorescent Ir(iii) complex as an acceptor was used to produce white-light-emitting organogels.

Rh-catalysed direct cyclisation of 1,4-naphthoquinone and 9,10-phenanthraquinone with alkyne: facile access to 1,8-dioxapyrenes and 1,12-dioxaperylenes as orange and red-emitting luminophores

Rh-catalysed direct cyclisation of quinones with alkynes has been accomplished through C–H activation strategy.

Recent progress in metal–organic complexes for optoelectronic applications

This critical review reports recent advances in the development of metal–organic complexes for optoelectronic applications.

A peptide based two component white light emitting system

A peptide based two component white light emitting system has been designed and developed on the basis of a co-assembly of a PDI containing peptide system as an acceptor and a stilbene containing peptide system as a donor in organic solvents.

Synthesis and electrophosphorescence of iridium complexes containing benzothiazole-based ligands

Four heteroleptic bis-cyclometalated iridium(III) complexes containing 2-aryl-benzothiazole ligands, in which the aryl is dibenzofuran-2-yl [Ir(O-bt)2(acac)], dibenzothiophene-2-yl [Ir(S-bt)2(acac)], dibenzothiophene-S,S-dioxide-2-yl [Ir(SO2-bt)2(acac)] and 4-(diphenylphosphoryl)phenyl [Ir(PO-bt)2(acac)], have been synthesized and characterized for use in organic light-emitting diodes (OLEDs). These complexes emit bright yellow (551 nm) to orange-red (598 nm) phosphorescence at room temperature, the peak wavelengths of which can be finely tuned depending upon the electronic properties of the aryl group in the 2-position of benzothiazole. The strong electron-withdrawing aryls such as dibenzothiophene-S,S-dioxide2-yl and 4-(diphenylphosphoryl)phenyl caused bathochromatic shift of the iridium complex phosphorescence. These iridium complexes were used as doped emitters to fabricate yellow to orange-red OLEDs and good performance was obtained. In particular, a maximum luminance efficiency of 58.4 cd A(-1) (corresponding to 30.6 lm W(-1) and 19%) with CIE coordinates of (0.45, 0.52) was achieved for Ir(O-bt)2(acac)-based yellow device. Furthermore, the yellow emitting Ir(S-bt)2(acac) was used to fabricate two-element white OLED that exhibited a high efficiency of 32.4 cd A(-1) with CIE coordinates of (0.28, 0.44).