Our investigations refer to highly efficient emitting materials used in organic light-emitting diodes (OLED). We are
especially interested in the possibility of shifting the emission wavelength in phosphorescent iridium(III) complexes.
Depending on the mesomeric and inductive behavior of different substituents, the emission spectrum can be varied by
introducing those substituents at various positions of the chromophoric ligand. Therefore, we synthesized Ir(ppy)<sub>3</sub>-
analogue complexes with nitrile, trifluoromethyl and methoxy groups at different positions of the ligand's phenyl ring to
determine the influence of the position and of each substituent on the emission spectrum. To further study the
adjustability we prepared several heteroleptic complexes and changed the ancillary ligand therein. In addition, we
developed a new and as yet unknown ligand system based on hetero five membered rings, cyclometalated to iridium to
generate homo- and heteroleptic complexes. Devices obtained with these emitting materials have shown high
luminescence efficiencies of up to 30 lm/W @ 500 cd/m<sup>2</sup>.
We investigated the effect of thermal stress, caused by the deposition of aluminum on top of an organic light emitting
diode (OLED), on the device performance and proved our simulated results by experimental tests. Concerning the
temperature of the substrate, we found a much larger influence of thermal radiation, caused by the evaporation source
and the environmental setting compared to the kinetic and thermal energy of the deposited material itself.
Due to these results, we developed a new system for metal deposition, using the flash-evaporation technique. Using it,
we were able to minimize the influence of thermal radiation and geometry on the evaporation. Therefore the substrate
heating was reduced by more than 90 % and the photometric efficiencies of test-devices were improved slightly.
Additionally the time of deposition and retention was lowered by 90 %, with an increased material yield of more than
55 % at the same time. The resistance of the conducting layer decreases by two orders of magnitude, caused by emerging
micro crystals. Surprisingly, the roughness of the surface actually decreased slightly.
Admittance spectroscopy is a simple yet powerful tool to determine the carrier mobility of organic compounds. One requirement is to have an Ohmic contact for charge injection. By employing a thin interfacial layer of tungsten oxide or molybdenum oxide we have found a possibility to efficiently inject holes into organic materials with a deep highest occupied molecular orbital level down to 6.3 eV. These results considerably enhance the application range of the admittance
spectroscopy method. The measured mobility data are in excellent agreement with data obtained by the time-of-flight technique. To efficiently inject electrons into materials with an ionization potential of up to 2.7 eV we thermally evaporated an intermediate layer of cesium carbonate and discuss the extracted electron mobilities.