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

We present an overview of the current status of our work on scanning-tunneling-microscope-based (STM) spectroscopy and electroluminescence (EL) excitation to study the physical and electronic structure of organic materials used in organic light-emitting devices (OLEDs). By these means we probe the critical device parameters in charge-carrier injection and transport, i.e., the height of the barrier for charge-carrier injection at interfaces between different materials and the energy gap between positive and negative polaronic states. In combination with optical absorption measurements, we gauge the exciton binding energy, a parameter that determines energy transport and EL efficiency. In STM experiments involving organic EL excitation, the tip functions as an OLED electrode in a highly localized fashion, allowing one to map the spatial distribution of the EL intensity across thin-film samples with nanometer lateral resolution as well as to measure the local EL emission spectra and the influence of thin-film morphology.