Organic Thin-film Light-emitting Diode Light-emitting Mechanism

Organic electroluminescent devices(OLEDs) have aroused many scientists' interests because of their potential adventages in low-power, emissive, flexible, cost-competitive, flat panel displays. Red, Green and blue light-emitting devices are readily avaible. So far, the investigation of the OLEDs has been the hotspot of the materals, physics and chemistry.In this paper, Carrier recombining and causing luminescence in single layer OLEDs and bilayer OLEDs was investigated. By solving the continuity equation for electrons and holes, the distribution of current density and recombination area were achieved. It is found that when μh>μe, the recombination area is lean to cathode and when μh<μe, is lean to anode.Based on the physical processes of carrier transport and recombination, a model which describing carrier transport and recombination in bilayer organic devices was presented. The results indicate that carriers recombining and causing luminescence in two organic layers by traversing their interface. The influence of barrier height of transport layer on current density, recombination current and recombination efficiency of the devices is great. In addition, it proved that the electric field could control the carrier recombination regions. Along with voltage hoisting,the recombination efficiency reached the max before it declines quickly.Meanwhile, the influence of doping on OLEDs and the mechanism of doped OLEDs were investigated intensely. It is found that there exists a correspondent relation between doping concentration and luminescence phenomena. As the increasing of concentration, the host and guest interconverted, and the more the charge been transferred, the more the total energy decreased.Finally, we deduce that the doping of Rubrene in PVK just acting as traps in electroluminescent devices ,and its trapping electrons arrested many cavities in PVK. And so, more PVK who didn't transport energy was concerned with trop and it makes less PVK was concerned with energy transfer in photoluminescent devices than in electroluminescent devices.