Microcavity structure consisting of distributed Bragg reflector and metal silver mirror is designed. The structure is glass/DBR/ITO/TPD/Alq

3

/Ag.The tris(8-hydroxyquinoline) aluminum(Alq

3

) is the electron transport layer and the emissive layer

and the N

N-diphenyl-N

N-bis(3-methyl-phenyl)-1

1′biphenyl-4

4′diamine(TPD) is the hole-transport layer. Compared to the electroluminescence(EL) spectra of non-cavity OLEDs

the linewidth of the MOLEDs is narrower

and the emission peak is enhanced. So the microcavity effect is very observable. In this work

the matrix method was adopted.The dependence of the electroluminescence(EL) spectra on the cavity length

the emitting layer thickness

the position of the interface between EML and HTL and the position of the emission region was analysed detailedly. In all calculation

the thickness and refraction of ITO and the thickness of the metal silver were kept constant. The results show: 1.with increasing the thickness of cavity

the normalized electroluminescence(EL)intensity decreased continually; 2.with increasing the thickness of the emitting layer

the normalized EL intensity discontinuously changed; 3.because the electron mobility in Alq

3

is different from the hole mobility in TPD

the emitted radiation was strongly dependent on the position of the emissive layer inside the cavity. Finally

the emission region should be narrow at the center of the electric field in the resonant cavity to optimize MOLED.