Study Of Dye-doped Organic Electrophosphorescent/white Light-emitting Device

White organic light-emitting device (WOLEDs) and phosphorescent organic light-emitting device (PHOLEDs) are highlighted nowadays in the research of organic light-emitting device (OLEDs). PHOLEDs have attracted much interests because of their highest internal quantum efficiency up to 100%, and WOLEDs have accelerated quickly due to the potential to become the new generation of solid state white light illumination and their use as backlighting for LCD displays. In this dissertation, a series of PHOLEDs and WOLEDs are manufactured, dealing with the study of the luminous process, color purity stability of the device and the energy relationship between the light-emitting layers from the aspect of device structrue, the luminous mechanism and the property of materials, etc. It mainly contains:(1) The influence of different matrix-dopant match on the device efficiency, luminance and color purity are investigated by doping the red phosphorescent material of Btp2Ir(acac) into TPBi, CBP and Alq matrix.The luminous differences of Btp2Ir(acac) in TPBi and CBP are studied. Compared with CBP matrix, TPBi has a better conduction ability for electrons which, in the light-emitting layer, is usually minorities, and decide on the performance of the device. So electrons can move relatively free in TPBi matrix than in CBP matrix, and hence have more chances of being captured by Btp2Ir(acac) moleculars. Then the excited Btp2Ir(acac) moleculars give out efficient phosphorescent emission. However, CBP matrix cannot conduct electrons well, which leads to forming a little electron-hole recombination zone and a small number of CBP excitons. What is more, CBP triplet excitons possess a big exciton diffuse length and can escape from electron-hole recombination zone easily, thus taking away the energy of the emission layer. So the emission of Btp2Ir(acac) in TPBi is stronger than in CBP. The emission of Btp2Ir(acac) in Alq has the poorest performance among three matrixs. Lack of appropriate energy level match between Alq and Btp2Ir(acac), and a short lifetime of Btp2Ir(acac) triplet excitons, should be responsible for the inefficient emission.We change the thickness of the emissin layer for TPBi matrix, and discuss the reason how the variety of the emissin layer influences the performance of the device by analysing the roll-off current vs the thickness of the emissin layer curve.We change the hole-trapping material Rubrene with phosphorescent dye Btp2Ir(acac) into CBP matrix. It is found that the luminous efficiency and luminance of the device decrease, and color purity of the device becomes better because of Rubrene' co-doping. We give the explaination from the aspect of luminous process of the device and the material property of Rubrene.(2) We co-dope blue fluorescent dye of BCzVB and red phosphorescent dye of Btp2Ir(acac) into CBP matrix. By changing the doping concentration of Btp2Ir(acac), the white emission is realized. Further more, it is observed that color purity of WOLEDs keeps stable with the increasing excited current density. The reasons are given to explain the stability of color purity from the aspect of the luminous mechanism and the energy relationship in the light-emitting layer. It is demonstrated that, high-efficiency and complete energy transfer from host CBP to dopant Btp2Ir(acac), incomplete energy transfer from blue dye of BCzVB to red dye of Btp2Ir(acac), in addition to BCzVB moleculars' availably capturing electrons and holes, which prevents Btp2Ir(acac) ' capturing cartier, jointly determine the stability Of color purity in WOLEDs.(3) We manufacture one-emission-layer and two-emission-layer PHOLEDs/ WOLEDs based on phosphorescent red dye of Btp2Ir(acac) and blue dye of Firpic. In one-emission-layer PHOLEDs, the energy relationship between two phosphorescent dye is studied. In two-emission-layer PHOLEDs, a spacer layer is inserted between the blue-light-emission layer and the red-light-emission layer. The energy relationship between the two layer and the function of spacer layer are studied.In Btp2Ir(acac) and Firpic co-doped one-emission-layer PHOLEDs, the blue emission of Firpic is almost annihilated completely by Btp2Ir(acac), which means in the co-doped system, there exists very efficient, complete energy transfer from the triplet excitons of the blue dye Firpic to the triplet excitons of the red dye Btp2Ir(acac).In the two-emission-layer PHOLEDs/WOLEDs, It is demonstrated that, there is no energy transfer between the blue-light-emission layer and the red-light-emission layer before the spacer layer is inserted. However, the chromaticity of the device red-shifts clearly after a 2nm spacer layer is inserted. The red-shift in chromaticity occurs due to the following process: CBP and Firpic excitons in the blue-light-emission layer transfer energy to Btp2Ir(acac) excitons in the red-light-emission layer via CBP excitons in spacer layer.