The intrinsic mechanisms of OLED degradation are investigated in this work. An increase of voltage and a decrease of luminance and efficiency of OLED under accelerated degradation conditions (i.e. constant high current) were observed in the experimental analysis. Degradation of OLED can be due to the decrease of charge carrier mobility, the change of electrode contact, or the formation of more traps. In this work an increase in the luminance ideality factor of OLED in diffusion regime has been observed from pristine to degraded device. Such increase of this value can either be interpreted as the deterioration of contact, which will change the current into injection limited. Or it can due to the formation of more traps, which brings the trap-assisted recombination more dominant. Further experiments have been carried out where the dependence of corresponding open-circuit voltage (Voc) on the incident light intensity (I) was investigated. From the 2.0kT/q enhancement of the Voc dependence on the logarithmic incident light intensity in the aged devices we could eliminate the influence of electrode contact change. Furthermore the formation of more traps during degradation is being investigated.
Max Planck Institute for Polymer Research
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