Influence of deposition rate on morphology and optical properties of Alq3, used as emitter in OLEDs

Abstract

Film deposition rates during vacuum evaporation influences the nucleation and growth of thin films affecting the film microstructure and hence the physical and device properties. The microstructure and surface morphologies of thin films affect the device behavior of OLEDs, particularly when films are very thin. We are reporting a systematic study on the role of film deposition rate in determining the microstructure of small molecular organic thin films. The study would be important for the throughput, performance and stability of OLED based displays and white lights. In this work, we deposited a large number of organic thin films of popular small molecular material Alq3 (Tris (8-hydroxyquinoline) aluminium) at a wide deposition range from ~1 to 100 A0/s. The influence of deposition rates on the surface roughness and optical constants of Alq3 films has been studied using atomic force microscopy (AFM), photoluminescence (PL), spectroscopic ellipsometry (SE) and Time Correlated Single Photon Counting (TCSPC) measurements. We find a correlation between deposition rates, film densities and surface roughness.