Highly Efficient, Deep‐Blue Doped Organic Light‐Emitting Devices

Abstract

In recent years, there has been considerable interest in developing blue organic light-emitting devices (OLEDs) with high efficiency, deep-blue color, and long operational lifetime. The deep-blue color is defined arbitrarily as having blue electroluminescent (EL) emission with a Commission Internationale de l'Eclairage y coordinate value (CIE y ) of < 0.15. Such emitters can effectively reduce the power consumption of a full-color OLED and can also be utilized to generate light of other colors by energy cascade to a suitable emissive dopant.It is well known that a guest-host doped emitter system can significantly improve device performance in terms of EL efficiency and emissive color, as well as operational lifetime.[1] Although many blue host materials have been reported, such as anthracene, [2] di(styryl)arylene, [3] tetra(phenyl)pyrene, [4] terfluorenes, [5] and tetra(phenyl)silyl derivatives, [6] blue-doped emitter systems having all the attributes of high EL efficiency, long operational lifetime, and deep-blue color, are rare. [7] This is because designing a fluorescent, deep-blue dopant capable of forming an amorphous glassy state upon thermal evaporation with a much shortened p-conjugation length is a rather daunting task. In addition, finding a deep-blue dopant with a small Stokes shift is essential for efficient Förster energy transfer from the host to dopant molecules, since the energy transfer efficiency is highly dependent on the spectral overlap between the emission of the host and the absorption of the dopant.Recently, we have successfully demonstrated an anthracene-based blue host material, 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN), which possesses a wide energy bandgap of 3.0 eV and can also form a stable thin-film morphology upon thermal evaporation. When doped with a di(styryl)-amine-based blue dopant, p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph), it achieved a very high EL efficiency of 9.7 cd A -1 , with a greenish-blue color of CIE x,y (0.16, 0.32) and a long operational lifetime of 46 000 h at a normalized initial brightness of 100 cd m -2 .[8] However, the color saturation of the blue-doped emitter system (DSA-Ph@MADN) is far from adequate for application in full-color OLED displays. On the other hand, the symmetrical di(styryl)amine-based organic molecule is well known to possess a high fluorescent quantum yield, [9] and its emission wavelength (k max = 450-480 nm) is dependent on the p-conjugation length, which encompasses the two strongly donating arylamine moieties. However, the molecular engineering of symmetrical di(styryl)amine-based fluorescent dyes to cause hypsochromic shift has its limitations as both donors are already present as part of the styryl p-conjugation.[10]In this paper, we report a series of novel, deep-blue dopants based on unsymmetrical mono(styryl)amine derivatives, which provide us with a basic structure for color tuning within the 430-450 nm spectral region. We show that when doped in the MADN host as an OLED, some of these deep-blue dopants exhibit a...

Highly efficient greenish blue-emitting organic diodes based on pyrene derivatives

“…The data showed that distyrylarylene host DPVBi (4,4 0 -bis(2,2-diphenyl-ethen-1-yl)-diphenyl) and distyrylarylene dopant BCzVBi (4,4 0 -(bis(9-ethyl-3-carbazovinylene)-1,1 0 -biphenyl) exhibit the highest luminous efficiency and external quantum efficiency among the materials that have been reported in the literature so far. There are great progresses for device fabrication techniques and materials development in the past decade [6][7][8][9]. However, further improvements in both the efficiency and brightness for blue OLEDs are still necessary.…”

Large scale production of novel g-C3N4 micro strings with high surface area and versatile photodegradation ability

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Blue organic light-emitting diodes using novel spiro[fluorene-benzofluorene]-type host materials

“…Although a large number of valuable red and green emitters that satisfy the requirements for OLEDs have been developed, efficient and stable blue emitters are still rare and have been the subject of considerable interest [1,2]. Major focus has been on various material systems, including anthracene [3][4][5], distyrylarylene [6][7][8][9][10][11], fluorene [12,13] and tetra(phenyl)silyl derivatives [14,15].…”