有机电致发光白光器件的研究进展

在十多年的时间里,有机电致发光二极管(Organic Lightemitting Diodes,OLEDs)的研究和应用取得了长足的进展。有机电致发光器件具有许多优点,例如:自发光、视角宽、响应快、发光效率高、温度适应性好、生产工艺简单、驱动电压低、能耗低、成本低等,因此有机电致发光器件极有可能成为下一代的平板显示终端。有机电致发光白光器件因为可以用于全彩色显示和照明,已成为OLED研究中的热点。介绍了有机电致发光白光器件的研究进展,按发光的性质将白光器件分为荧光器件和磷光器件两类,按发光层数将白光器件分为单层和多层器件,对相关材料、器件结构、发光机理等方面进行了讨论。

Progress of White Organic Light Emitting Diodes

In the past decade, electroluminescent devices based on organic materials are of considerable interest to their attractive characteristics and potential applications. The study and application of organic light emitting have made significant progress. Organic light emitting devices (OLEDs) have many advantages such as their thinness, self light emission, broad viewing angle, quick response, high efficiency, easy fabrication, low driving voltage, low energy consumption, low cost, etc. It is therefore very possible that they will become the next generation of panel displays. White organic light emitting devices have been attracting particular attention nowadays due to their potential applications as full color displays, backlights for liquid crystal displays and even paper thin next generation of light sources. The emitting materials used in OLEDs can be divided into fluorescent and phosphorescent materials. Phosphorescence is distinguished from fluorescence by the speed of the electronic transition that generates luminescence. Both processes require the relaxation of an excited state to the ground state, but in phosphorescence the transition is "forbidden" and as a consequence it is slower than fluorescence, which arises from allowed transitions. Indeed, phosphorescence may persist for several seconds after a phosphorescent material was excited, whereas fluorescent lifetimes are typically on the order of nanoseconds. Interest in phosphorescence, and the phosphorescence of organic materials in particular, arises from the application of these materials to organic light emitting devices (OLEDs), where it is found that the luminous efficiency may be improved by up to a factor of four over that obtained using fluorescence. This increase is fundamental to organic materials and arises during the formation of an excited state (or excitons) from the combination of electrons and holes. To achieve white emission in OLEDs, an additive mixture of the three primary colors or two complementary colors are required. Various methods have been demonstrated to produce white light emission from organic OLEDs, including mixing of the three primary colors (red, green and blue, RGB) from respective layers in a multilayer structure, doping a single host emissive layer with RGB emitting materials, or utilizing of broad exciplex or excimer emission. White emission could also be achieved by mixing a blue host with an appropriate amount of yellow or orange dopant in a single emissive layer. The development of white organic light emitting diodes has been described and discussed on the materials, the device structures and the light emitting mechanisms have also been given.