Abstract: Based on the experience formula and the triplet (T) -triplet (T) annihilation processes,an analytical model to calculate the recombination width and the external quantum efficiency of doped organic electrophosphorescence (EPH) devices is presented.The influences of applied bias,current density, and device thickness on the width of the recombination zone and the external quantum efficiency are studied thoroughly.It is found that:(1) as the applied voltage increases,the recombination width of the device decreases and the external quantum efficiency increases;(2) with increasing the thickness of the device,the recombination width increases accordingly,and the external quantum efficiency behaves differently at different applied voltages;(3) the external quantum efficiency decreases significantly with increasing the recombination current density.

Key words: electrophosphorescence, triplet state, recombination width, external quantum efficiency