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

Abstract

In this study, the authors show an empirical guideline for designing hole transportmaterials (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 ( Al q 3 ) ( 50 nm ) ∕ Mg Ag ( 100 nm ) ∕ Ag ( 10 nm ) , the authors compared electroluminescencecharacteristics 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.