OLED(organic light emitting diode) is a very attractive candidate as display devices and for(various) applications.Since Tang

et al

.reported on organic electroluminescence devices

OLED has been widely studied by many researchers and developed as commercial products.Because OLED has a lot of merits from the viewpoint of mobile display such as low power consumption

light weight and thinness

many efforts are(being) made to develop a robust mobile display with OLED.At recent years

in order to improve OLEDs' luminescence-efficiency

much research has been done.However

improving carriers' recombination-efficiency is one of valid approach to improve OLEDs' luminescence-efficiency.Carriers' recombination-efficiency is connect with structures of devices and parameters of materials.So it is necessary to build a model of carriers' transport and recombination for finding out the relation between carriers' recombination-efficiency and the structure or parameters.In this paper

we attempt to build a model of carriers' transport and recombination on the classical bilayer OLEDs.In our experiments

a classical bilayer OLED(ITO/TPD/Alq

3

/Al) is fabricated by thermal evaporation method.We have test the property of the OLED.The result showed that the electricity-voltage relation accords with Fowler-Nordheim tunneling injection theory very well.Basing on Fowler-Nordheim's theory

analyzing the distribution of currents theoretically

and deducing mathematically

a model for carries transport and recombination on the classic OLEDs is presented.According to this model

we analyze carriers' transport and recombination process theoretically and probe into the expression of carriers' recombination-efficiency.Further more

under this model

a formula between the recombination-efficiency and the surface-density of charged carriers

including holes which congregate at the interface on the anode side and the electrons which congregate at the interface on the cathode side

is educed.In this formula

the macroscopic variable (carriers' recombination-efficiency) is expressed by microscopic variables(surface-density of charged car-(riers)).It can offer some theoretical foundation for improving the efficiency of charged carriers recombination in OLEDs from microcoscopic mechanism.