Space-charge limited conduction with a field and temperature dependent mobility in Alq light-emitting devices

Electrical transport in organic Light-emitting devices (OLEDs) based on tri s(8-hydroxyquinolato)aluminium (Alq) is investigated as a function of tempe rature and organic layer thickness. It is shown that the thickness dependen ce of the current provides a unique criterion to discriminate between (1) i njection limited behavior, (2) trap-charge limited conduction with an expon ential trap distribution and a field independent mobility, and (3) trap-fre e space charge limited conduction with a field and temperature dependent mo bility. The observed thickness and temperature dependent current-voltage ch aracteristics are found to be in excellent agreement with trap-free SCLC wi th a hopping type charge carrier mobility. (C) 2001 Elsevier Science B.V. A ll rights reserved.