Improving the lifetime of a polymer light-emitting diode by introducing solution processed tungsten-oxide

We report a polymer light-emitting diode (PLED) using solution processed tungsten-oxides (WO_x). Coating of a thin WO_x layer on PEDOT:PSS increases the current efficiency of PLED from 9.11 to 9.90 cd A ^-1 because of the improved conductivity of the PEDOT:PSS due to the incorporation of WO_x. Improvement of the conductivity of PEDOT:PSS promotes hole injection into the emission layer. The lifetime of a PLED with WO_x layers on both sides of PEDOT:PSS is 1.8 × 10⁶ h which is around 20 times longer than that of the control device at 1000 cd m^-2. The enhanced lifetime is due to the suppression of the indium diffusion from ITO to PEDOT:PSS by WO_x and also due to the prevention of acidic damage that can occur to ITO and the organic emission layer by sulfate ions in PEDOT:PSS.