Characterization and optimization of the deposition process of aluminum top electrodes for organic devices

Abstract

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.