BLUE ELECTROLUMINESCENT DIODES UTILIZING BLENDS OF POLY(P-PHENYLPHENYLENE VINYLENE) IN POLY(9-VINYLCARBAZOLE)

We report blue light emission from diodes made from polymer blends com posed of poly(p-phenylphenylene vinylene) (PPPV) in a hole-transportin g polymer, poly(9-vinylcarbazole) (PVK). The soluble PPPV and PVK allo w fabrication of light-emitting diodes (LEDs) by spin-casting the elec troluminescent polymer blend from solution at room temperature with no subsequent processing or heat treatment required. The initial devices utilized calcium as the electron-injecting (rectifying) contact on th e front surface of a PPPV/PVK film spin-cast onto a glass substrate pa rtially coated with a layer of indium/tin oxide (ITO) as the hole-inje cting contact. The LEDs turn on at approximately 30 V and have a peak emission wavelength in the blue at 495 nm (at room temperature). The q uantum efficiency is measured as a function of PPPV content in the ble nd; the maximum efficiency is approximately 0.16% photons/electron at a concentration of only 2% PPPV in PVK.