STM-excited electroluminescence and spectroscopy on organic materials for display applications

We present an overview of the current status of our work on scanning-tunnel ing-microscope-based (SIM) spectroscopy and electroluminescence (EL) excita tion to study the physical and electronic structure of organic materials us ed in organic light-emitting devices (OLEDs). By these means we probe the c ritical device parameters in charge-carrier injection and transport, i,e,, the height of the barrier for charge-carrier injection at interfaces betwee n different materials and the energy gap between positive and negative pola ronic states. In combination with optical absorption measurements, we gauge the exciton binding energy, a parameter that determines energy transport a nd EL efficiency, In STM experiments involving organic EL excitation, the t ip functions as an OLED electrode in a highly localized fashion, allowing o ne to map the spatial distribution of the EL intensity across thin-film sam ples with nanometer lateral resolution as well as to measure the local EL e mission spectra and the influence of thin-film morphology.