Blue electroluminescence in organic semiconductors

Abstract

793-805Light emitting diodes based on organic materials are of considerable interest owing to their attractive characteristics and potential applications in flat panel displays. This paper focuses on some important blue light emitting organic materials. Particularly the attention has been paid to the absorption, photoluminescence (PL), electroluminescence (EL) spectra, current-voltage (1-V) and luminescence-voltage <span style="mso-bidi-font-family:Arial; mso-bidi-language:HI">(L- V) characteristics of blue light emitting organic semiconductors, as well as those of the para-hexaphenyl (PHP). Syntheses of some important blue light emitting materials have also been discussed. Para hexaphenyl (PHP), which was synthesized by the conventional Kovacic method, is one of the important blue light emitting π-conjugated oligomers. OLEDs fabricated, using PHP as an emitter, TPD and PBD as the hole transport layer and electron transport layer respectively, gave efficient blue electroluminescence. The photoluminescence (PL) and electrolurninescence (EL) of PHP occur at 423 nm, indicating PHP as an excellent blue emitter. This oligomer showed strong absorption peaks at 297 and 318 nm. The devices showed non-linear electrical properties and bright electroluminescence with low turn on voltages (9V). Some of our most recent work in the development of a variety of blue light emitting devices has been included and discussed in detail. </span