有机电致发光材料分子与器件结构设计

Design of the Organic Light-emitting Materials and the Structure of the Organic Light-emitting Devices

有机电致发光器件是当今显示器件领域的研究热点 ,越来越多的人们致力于开发高性能的发光材料和研制高效率的器件结构。本文就有机发光材料的分子结构设计 。

Organic light emitting devices (LEDs) have attracted much attention due to their potential application for flat panel displays. People apply themselves to develop the light emitting materials with high performance and light emitting devices with high efficiency and stability. In this paper, we discuss the design of the molecular structure and the method to improve the emitting characteristics of the LEDs. The materials used for the LEDs include light emitting materials, carrier transporting materials, and electrode materials. The performance of these materials can be optimized by the design of the molecular structure. The materials with good performance must have high photoluminescent quantum efficiency, good carrier transporting ability and thermal stability. To date, efficiencies for organic LEDs have been limited by the use of fluorescent emissive materials. This limit arises since fluorescence only involves singlet relaxation, thus eliminating the participation of the triplet exciton population. By employing a phospherescent dye where both singlet and triplet excited states participate, the LEDs internal efficiency can, in principle, be increased by as high as 100%. Another method to improve the emitting efficiency is that employing the Frster excitation energy transfer process. Blending a donor with an emitting acceptor for the energy transfer highly reduces the concentration quenching of the generated excitons. Therefore, the energy transfer in the blend systems works effectively to improve the external quantum efficiency of the light emitting diodes. But it is difficult for the doping system to produce red LEDs with high luminance efficiency. Because the energy transfer from host to guest is not very complete due to the weak overlap between the emission of host and the absorption of red dyes, and in addition, the concentration quenching at high doping concentration. Recently, there are some reports to use two step energy transfer to increase the emission characteristics of organic LEDs. The emitting layer of the LEDs are co doped with three different fluorescent materials (A, B and C), and the energy transfer process is from A to B and then from B to C, which is a promising method for obtaining red LEDs. The structure of the LEDs is important for the improvement of the brightness and emitting efficiency of the LEDs. When design the structure of the LEDs, the match of the energy band and layer thickness and refractive index, and the balance of the injected carriers between the carrier transporting and emitting layers must be taken into account.