Phosphorescent Organic Light Emitting Diode Using Vinyl Derivatives of Hole Transport and Dopant Materials

Abstract

Organic light-emitting diodes (OLEDs) were prepared by a deposition polymerization method, in which vinyl monomers were evaporated and then annealed after deposition. N,N'-diphenyl-N,N'-bis(4-vinylphenyl)benzidine (DvTPD) was used both for a hole transport layer (HTL) and for the host material of an emissive layer (EML). bis(1-phenylisoquinoline)acetylacetonate iridium(III) [Ir(piq)2acac] and its styryl derivative bis(1-phenylisoquinolinate)-6-(4-vinylphenyl)acetylacetonate iridium(III) [Ir(piq)2acac-vb] were used as dopants. Ir(piq)2acac and Ir(piq)2acac-vb showed comparable emission characteristics. The device lifetime was improved by the thermal polymerization of DvTPD, and it was further improved by polymerizing both the host and dopant molecules to form a copolymer instead of a molecularly dispersed EML. In addition, the device with a codeposition-polymerized EML showed a small tendency of luminescence efficiency to decrease with increasing luminance. Deposition polymerization, achieved by evaporating vinyl monomers followed by thermal annealing, can be a promising method for constructing OLED structures.