Charge Carrier Mobility in Vacuum-Sublimed Dye Films for Light-Emitting Diodes Studied by the Time-of-Flight Technique

The Charge carrier mobility has been examined for a representative organic hole transport material TPD and a host material CBP, doped with a fluorescent dye, rubrene and Ir(ppy)3, by time-of-flight (TOF) technique. Decreasing of hole mobilities of the dye-doped films can be explained by a carrier-trapping model and the ionization potential difference of TPD and CBP. We successfully measured an electron mobility of the rubrene-doped TPD films, and Ir(ppy)3-doped CBP films, while the mobility could not measured non-doped TPD and CBP films. The EL process of the dye-doped systems is discussed in terms of the electron transfer properties of emission layer.