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.

A high triplet energy (E-T = 3.2 eV) electron transporting/hole blocking (ET/HB) material, 1,2,4,5-tetra (3-pyrid-3-yl-phenyl)benzene (TemPPB) with a super twisted structure and high thermal stability has been synthesized. An external quantum efficiency (EQE) of 19.6% was achieved by using TemPPB as the ET/HB material in a blue electrophosphorescent device, much higher than the EQE of 12.5% for the device using the conventional ET material, 3-(4-biphenyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ). In addition, the weak ET property of TemPPB resulting from its super twisted structure can be enhanced via n-type doping with LiF. An EQE of 24.5% was achieved by combining n-type doping and a double-emission layer. This shows an alternative way to design ET/HB materials with high E-T and improved thermal stability for blue electrophosphorescent devices.

The interface between an electrode and the organic active layer is an important factor in organic solar cells (OSCs) that influences the power conversion efficiency (PCE). In this report, a buffer layer of 2-thenylmercaptan/Au self-assembly film is introduced into OSCs as a substitute for the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS) layer. The electrode/active layer interface is meliorated by Au-S coordinate bond of self assembly after applying this buffer layer. The series resistance reduces from 20 Omega cm(2) in a device based on PEDOT:PSS to 10.2 Omega cm(2). Correspondingly, the fill factor (FF) increases from 0.50 to 0.64. Moreover, due to the dipole of this self-assembled layer, the open circuit voltage (V-oc) also increases slightly from 0.54 V to 0.56 V and the PCE reaches 2.5%. (C) 2010 Elsevier B.V. All rights reserved.