To improve the characters of organic light emitting diodes (OLEDs)

the mechanism of electroluminescence processes has been studied extensively

but due to the complexity of mathematics and experiments

most of them have not been solved. In this paper we try to solve this problem by adding the injection and the recombination of carries to a model which H.Bassler and co-workers have proposed. Using Monte-Carlo method we simulated the injection

transport

and recombination of carriers in the OLEDs

and we obtained the time-dependent diffusion coefficient of δ electronic pulse

then we extended the diffusion coefficient of δ electronic pulse to the diffusion coefficient of direct current. The relationship between diffusion coefficient

electric field and standard deviation of density of states (σ) was obtained. We found that relationship between diffusion coefficient and electric field is non-linear

and it lies on the magnitude of standard deviation of density of states (σ). With increasing σ

the variance of diffusion coefficient changing with electric field became much greater. If taking into account the recombination type: Langevein type

r

=4π

<

R

>

(

D

+

+

D

-

) at the same time

we can get the relationship between recombination coefficient and electric field. Then we discussed the spectrum deforming with electronic field of ITO/ROPPV(60nm)/Alq(40nm)/Al structure. In our simulation

it is the standard deviation of density of states (σ) that controls the variance magnitude. The standard deviation of density of states (σ) tells disorder degree of samples and can be adjusted by changing the temperature of substrate and growing velocity in developing sample. In fact the reason influencing the deformation of spectrum is the relative magnitude of σ

so if we find a way to diminish σ

we can decrease the variance of recombination coefficient. But it also decreases the magnitude of mobility and decreases the luminescence efficiency. There exists a best σ value improving the characters of OLEDs. With this method

we have a new way to design the OLEDs.