Material design of hole transport materials capable of thick-film formation in organic light emitting diodes

In this study, the authors show an empirical guideline for designing hole transport materials (HTMs) that suppress rises in driving voltage even with a few hundred nanometer thick film in the organic light emitting diodes (OLEDs). In a device structure of indium tin oxide (110 nm)/hole transport layer (HTL) (X nm)/4,4(')-N,N-'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (10 nm)/tris-(8-hydroxyquinoline)aluminum (Alq(3)) (50 nm)/MgAg (100 nm)/Ag (10 nm), the authors compared electroluminescence characteristics of the OLEDs having a thin-film HTL (X=50 nm) and a thick-film HTL (X=300 nm) using 13 kinds of HTMs. They observed a closed correlation between suppression of the driving voltage and the HTMs' thermal characteristics. Highly thermally stable HTMs resulted in a small increase in the driving voltage. (c) 2007 American Institute of Physics.