OLED matrix displays: in-line process technology and fundamentals

Abstract

For more than a decade considerable effort has been put into the development of light emitting devices based on evaporated layers of organic semiconductors. To date, the properties of matrix displays consisting of organic light emitting diodes (OLEDs) basically meet automotive and consumer product requirements. OLED matrix displays offer high contrast, wide viewing angle and a broad temperature range at low power consumption. Due to the sensitivity of organic thin films, device structuring by conventional etching techniques is not feasible and alternative structuring techniques were developed. To meet industrial demands for device fabrication an in-line-OMBD was developed. For the first time ever, a fully in-line processed OLED is presented. Electrical current in organic devices is limited by the low conductivity of organic semiconductors and by energy barriers at the metal–organic semiconductor interface. Photoelectric measurements facilitate the determination of barrier height differences between various electrode setups. Further insight in the energy band alignment at organic heterointerfaces is gained by ultraviolet photoelectron spectroscopy (UPS). In addition to widely employed electrical ( I– V, C– V) and optical ( P– I) measurements, thermally stimulated current (TSC) and luminescence (TSL) allow the characterization and a more detailed understanding of carrier traps and charge transport in organic devices. Energy transfer in a doped OLED emitting layer can be investigated by time-resolved photoluminescence measurements.