Recent Progresses on Materials for Electrophosphorescent Organic Light‐Emitting Devices

Abstract

Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

Solution-Processed Blue/Deep Blue and White Phosphorescent Organic Light-Emitting Diodes (PhOLEDs) Hosted by a Polysiloxane Derivative with Pendant mCP (1,3-bis(9-carbazolyl)benzene)

“…[32][33][34][35] The small-molecule mCP [1,3-bis(9-carbazolyl)benzene] which has a triplet energy of 2.9 eV is widely used in this context. [36][37][38][39][40][41] However, mCP tends to crystallize as a consequence of its rather low T g (glass transition temperature, 60 °C). It is a challenge to develop a polymeric host that has a higher T g than mCP while maintaining mCP's desirable optoelectronic properties.…”

Cyclometalated Ir(III) Complexes for High-Efficiency Solution-Processable Blue PhOLEDs

“…They have the benefits of relatively short excited state lifetimes, high photoluminescence efficiency, good color tuneability and general thermal and electrochemical stability. 4,5,6 In this context the archetypal complex is the green emitter fac-Ir(ppy) 3 (ppy = 2-phenylpyridine). For blue emission electron-withdrawing substituents are attached to the phenyl ring of ppy ligands to decrease the HOMO energy while keeping the LUMO energy relatively unchanged.…”

Fabrication and characterization of green light emitting diode

“…OLEDs based on phosphorescent transition metal complexes are attracting significant attention since they can greatly improve electroluminescence (EL) performance as compared with the conventional fluorescent OLEDs [11][12][13]. According to spin statistics, the EL from small molecular fluorophores cannot exceed a maximum quantum yield of 25%, but in phosphorescent complexes, the EL can theoretically achieve quantum yields of up to 100% since both triplet and singlet excitons can be harvested for the emission [14].…”