The Model Of Carriers' Transport And Recombination In OLED And A Study On Phosphorescent Dye Doped OLED

On the basis of classical double-layer Organic Light Emitting Diode (OLED) (ITO/TPD(30nm)/Alq₃(40nm)/Al), some work has been done as follow:(1) Basing on Fowler-Nordheim's theory, a model for carders transport and recombination in the classical OLED is proposed. Further more, a formula about the recombination efficiency and the surface-density of charged carriers, including holes which congregated at the interface on the anode side and the electrons which congregated on the cathode side, is educed, and it offers some theoretical foundation for improving the efficiency of charged carriers recombination in OLED.(2) Phosphorescent OLED with 8-hydroxyquinoline aluminum(Alq₃) doped 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphineplatinum(Ⅱ)(PtOEP), which is a high efficient phosphorescent dye, are fabricated. The mechanism for energy transfer leading to electroluminescence of the phosphorescent dye in the films of Alq₃ host doped PtOEP guest is investigated. Based on the analysis of EL spectra, the mechanism of energy transfer and the optical properties between PtOEP and Alq₃, 10% (by weight) doping concentration is found to be the optimal concentration among 5%, 10% and 20% doping concentration. The external quantum efficiencies (QE) of the diodes with 10% PtOEP doping concentration and Alq₃ only are calculated according to the current density-voltage and luminescence-voltage data.(3) Two experiments are designed to determine the Alq₃ triplet diffusion length and transfer length in PtOEP doped layer through employing the phosphorescent dye (PtOEP) and fluorescent dye (DCM1). According to Alq₃ triplet diffusion length, transfer length and the thickness of the doped layer, the transfer efficiency of triplet excitons from Alq₃ to PtOEP is obtained. Further more, the ratio of the undoped diode's external QE to doped diode's is deduced. And the ratio is consistent with the experimental results.