Organic light emitting diodes using NaCl:N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)benzidine composite as a hole injection buffer layer

Composite buffer layers of N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)benzidine (NPB) and NaCl at the anode/organic interface were found to be very effective on the hole injection enhancement from an indium tin oxide anode to the hole-transport layer (HTL) of NPB. Two maxima of significant current injection with respect to compositional variation were observed, implying multiple injection mechanisms of the tunneling effect and other interfacial effects. From a longer operation lifetime, the enhanced device stability was also confirmed as compared with a standard device with copper phthalocyanine as the hole injection layer. Those results are partly attributed to the better mechanical contact between anode and HTL via the composite buffer, observed from atomic force microscopy measurement.