Temperature dependence of electroluminescence in a Tris-(8-hydroxy) quinoline aluminum (Alq3) light emitting diode

Organic electrolumisescent devices using tris-(8-hydroxy) quinoline aluminu m (Alq(3)) as the emissive layer and N,N ' -diphenyl-N,N ' bis (3-methylphe nyl)-[1-1 ' -biphenyl]-4-4 ' -diamine as the conventional hole transport la yer have been fabricated, The temperature- and field-dependent quantum effi ciency have beers investigated over the temperature range from 1 to 300 K u sing a model developed by Shen et al. [1] to explore the physics at the org anic heterointerface in the present device structure with the formation of an accumulation layer, It has been observed that electron luminescence inte nsity decreases with decreasing temperature down to 160 K, then saturates i n the low-temperature region. The quantum efficiency increases with decreas ing temperature and finally reaches an almost constant value. From the anal ysis, it is seen that the model can explain the luminescence behavior of th e device satisfactorily down to 120 K but fails to explain the low-temperat ure behavior. The efficiency has also been studied with voltage and it is s een that there is an optimum voltage required to get the maximum efficiency .