Blue electroluminescent diodes utilizing blends of poly(p-phenylphenylene vinylene) in poly(9-vinylcarbazole)

Abstract

We report blue light emission from diodes made from polymer blends composed of poly(p-phenylphenylene vinylene) (PPPV) in a hole-transporting polymer, poly(9-vinylcarbazole) (PVK). The soluble PPPV and PVK allow fabrication of light-emitting diodes (LEDs) by spin-casting the electroluminescent 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 the front surface of a PPPV/PVK film spin-cast onto a glass substrate partially coated with a layer of indium/tin oxide (ITO) as the hole-injecting contact. The LEDs turn on at ∼30 V and have a peak emission wavelength in the blue at 495 nm (at room temperature). The quantum efficiency is measured as a function of PPPV content in the blend; the maximum efficiency is approximately 0.16% photons/electron at a concentration of only 2% PPPV in PVK.