Multilayer Polymer Light-Emitting Diode Based on a Water Soluble Non-conjugated Polymer with Metal Ions

We have fabricated a polymer light-emitting diode (PLED) from a conventional blue-emitting polymer, polyfluorene (PFO), by constructing a multilayer structure with a metal-ion containing water- soluble non-conjugated polymer, polyurethane with Cs+ ions (PU: Cs+), on the top of the PFO. The device with the PU: Cs+ layer shows a maximum luminance of 4900 cd/m2 at an applied voltage of 10 V while the one without the PU: Cs+ layer shows only 2600 cd/m2 at the same applied voltage. We propose that improved device performance with the PU: Cs+ layer is due to not only an effective hole blocking at the polymer-polymer interface but also an increase in electron injection because of Coulomb attraction between the ions and electrons. We will discuss the effect of the multilayer polymer structure in a PLED in terms of the current/voltage characteristics, the luminance, and the quantum efficiency as functions of the applied bias. KCI Citation Count: 0