Temperature Dependence of Electroluminescence in tris-(8-hydroxy) quinoline aluminum (Al_(q3)) Light Emitting Diode

摘要

Organic electroluminescent devices using tris-(8-hydroxy) quinoline aluminum (Al_(q3)) as the emissive layer and N, N'-diphenyl-N,N' bis (3-methylphenyl)-[l-l'- biphenyl] -4-4'-diamine (TPD) as the conventional hole transport layer have been fabricated. We tried to explore the charge transport mechanisms in the OLED device by the studying of temperature dependent luminescence over the temperature range from 10K to 300K. We found that first, at lower applied voltage, two peaks have been observed in the quantum efficiency with temperature, and they are due to deep trap levels (high temperature regime) and shallow trap levels (low temperature regime). With increasing voltage, the high-temperature peak shifts toward lower temperature but no significant shift of the low-temperature peak is observed, and when the voltage is over 10 V, superposition of the peaks causes the apparent saturation in the low temperature regime of the quantum efficiency. Second, up to a certain temperature luminescence intensity decreases with decreasing temperature and then saturated in the low temperature region. The quantum efficiency increases with decreasing temperature and finally reaches to almost a constant value. Meanwhile we tried to use Frenkel exciton model to explain the luminescence behavior of the device.