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

Abstract

Electrical transport in organic light-emitting devices (OLEDs) based on tris(8-hydroxyquinolato)aluminium (Alq) is investigated as a function of temperature and organic layer thickness. It is shown that the thickness dependence of the current provides a unique criterion to discriminate between (1) injection limited behavior, (2) trap-charge limited conduction with an exponential trap distribution and a field independent mobility, and (3) trap-free space charge limited conduction with a field and temperature dependent mobility. The observed thickness and temperature dependent current–voltage characteristics are found to be in excellent agreement with trap-free SCLC with a hopping type charge carrier mobility.