Efficient White Organic Light‐Emitting Devices Based on Phosphorescent Platinum(II)/Fluorescent Dual‐Emitting Layers

Abstract

White organic light-emitting devices (WOLEDs) are of great interest because they can be used in full-color flat-panel displays with color filters, backlight panels, and as alternative lighting sources. [1][2][3] Electrophosphorescent WOLEDs are widely considered to be the most attractive because of their high quantum and power efficiencies. In comparison with their fluorescent counterparts which can only harvest singlet excitons, phosphorescent OLEDs are able to harness both singlet and triplet excitons generated by electrical injection. This leads to a fourfold increase in efficiency compared to that achievable in singlet-harvesting fluorescent OLEDs.[4] White phosphorescence can be obtained from iridium(III) complexes using multiple emitting layers (EMLs), [5,6] multiply doped emissive-layer architectures, [7] or semiconducting polymer blends. [8,9] So far, the highest external quantum efficiency (g ext ) and power efficiency (g p ) achieved have been 12 % [7] and 57 lm W -1 , [10] respectively. Although the performance of phosphorescent WOLEDs have been impressive, blue electrophosphorescent devices have been shown to have short operational lifetimes that limit the color stability of all-phosphordoped WOLEDs.[11] On the other hand, the emission of the reported iridium(III) complexes usually spans about one third of the visible spectrum, [12] and more than two phosphorescent dopants are usually required to achieve balanced white-light emission. Such multiemissive-layer WOLEDs are potentially costly and complicated to fabricate. Consequently, there is a going interest in the development of WOLEDs that have high efficiencies but relatively uncomplicated architectures.To fabricate high-efficiency WOLEDs that have a relatively uncomplicated architecture, it is necessary to develop new phosphorescent materials with a broad emission spectrum and sufficiently high luminous efficiency. Herein, we describe the construction of high-efficiency WOLEDs with a phosphorescent/fluorescent dual-emitting architecture. We used fluorescent material 9,10-bis-(b-naphthyl)-anthrene (DNA) as a blue-light source to overcome the color-stability limitations found for all-phosphor-doped WOLEDs, and phosphorescent platinum(II) complexes [(RC^N^N)PtCl] (RC^N^N)PtCl) = 3-(6′-(2″-naphthyl)-2′-pyridyl)isoquinolinyl and derivatives) as an orange or green-yellow guest, doped into a 4,4′-N,N′-dicarbazole-biphenyl (CBP) host, to achieve balanced white light. The green-yellow or orange phosphorescent platinum(II) complexes described in this work contain extended p-conjugated cyclometalated ligands and exhibit broad emission spectra coving two thirds of the visible spectrum.[13] This is a significant advance towards the ultimate realization of whitelight emission using the smallest number of dopants. Although a phosphorescent/fluorescent dual-emitting architecture has recently been reported by Forrest's group, [14] there is a key difference between this study and Forrest's work. Forrest's WOLEDs are four-component devices, employing two fluorescent ...

Synthesis, photophysical and electrophosphorescent properties of mononuclear Pt(II) complexes with arylamine functionalized cyclometalating ligands

“…Cyclometalated platinum(II) complexes have attracted a great deal of attention because of their applications in optoelectronic devices [1][2][3][4][5][6][7], chemical sensing [8][9][10], biochemistry [11] and supramolecular chemistry [12]. Various cyclometalated ligands, such as p-conjugated bidentate [(C^N) motif] [13][14][15][16][17][18][19][20][21][22], tridentate phenylsubstituted pyridine [(N^C^N) motif] [23][24][25][26][27] and bipyridine [(C^N^N) motif] [28,29] as well as the related diphenyl-substituted pyridine [(C^N^C) motif] [30][31][32] systems, have been extensively investigated.…”

Correlation between host material compositions and performances in organic white-light-emitting diodes with blue/orange/blue emitting stacked structure

“…In particular, multi-stacked emitting layers structure has been known to give good color stability, good color tuning and high efficiency due to the control of charge distribution [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The change of number of stacked emission layers and/or thickness of emitting layers were popular ways to control color performances of PHWOELDs although doping concentration management and energy level matching of organic layers have been developed as an approach to tune device performances of OWLEDs.…”

Control of device performances of phosphorescent white organic light-emitting diodes by managing charge transport properties of host materials

“…In recent years, many device architectures of white organic light-emitting diodes (WOLEDs) have been developed to improve their efficiency, luminance, color coordinates, and color stability [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Among them, WOLEDs based on stacked emitting structures are gaining interest due to their merits of high luminance and quantum efficiency.…”