AVS 47th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+EL+SS-WeM

Invited Paper OF+EL+SS-WeM1
The Transport and Injection of Positive Carriers in Conjugated Electroluminescent Polymers and their Devices

Wednesday, October 4, 2000, 8:20 am, Room 313

Session: Transport and Device Issues in Organic Thin Films
Presenter: A.J. Campbell, University of Sheffield, UK
Authors: A.J. Campbell, University of Sheffield, UK
D.D.C. Bradley, University of Sheffield, UK
H. Antoniadis, Infineon Technologies Corp.
Correspondent: Click to Email
Organic light emitting diodes (OLEDs) based on electroluminescent conjugated polymers are an important emerging technology with a wide range of display and lighting applications. Polyfluorene and its copolymers are considered to be amongst the most promising materials for use in commercial OLEDs. Indium tin oxide (ITO) is also the hole injecting electrode of choice in any practical device. Here we report the results of time-of-flight measurements on the transport of positive carriers in polyfluorene and its copolymers. The field and temperature dependence of the charge carrier mobility is compared to theoretical models for charge transport in disordered organic materials. We also report the results of dark injection and current density-voltage measurements on the injection of holes from differently prepared ITO contacts. The absolute injection efficiency of the contacts is calculated by comparison to trap-free, space-charge-limited current (TFSCLC). The injection efficiency is shown to vary with not only polymer ionisation potential but also with the nature of the ITO preparation (i.e. washed in solvents, exposed to an oxygen plasma, coated with a film of poly(ethylenedioxythiophene) / polystyrenesulphonic acid). The variation of the injection efficiency with temperature is also reported.