Organic semiconductors: fundamentals and applications

The first organic light emitting diodes (OLEDs) were demonstrated in 1987. To date they have been brought into marketable commodity. 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, new structuring techniques had do be developed. In recent years in addition to advanced OLED activities, increasing effort has been put into the realization of organic integrated circuits for low-cost applications based on organic field-effect transistors. First transistors have shown the necessity to decrease operating voltage and to improve carrier mobility. 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 are gained by ultraviolet photoelectron spectroscopy. Energy transfer, in a doped OLED emitting layer can be investigated by time-resolved photo-luminescence measurements.