Dependence of the amorphous structures and photoluminescence properties of tris(8-hydroxyquinolinato)aluminum films on vacuum deposition conditions

For further development of organic light-emitting diodes (OLEDs), an understanding of the amorphous structures and photoluminescence properties of organic emitting layers is needed. In this study, the molecular orientation, density, and photoluminescence properties of tris(8-hydroxyquinolinato)aluminum (Alq₃) films vacuum-deposited using various substrate temperatures and deposition rates were investigated. The molecular orientation and density of the Alq₃ films exhibited clear dependence on the substrate temperature, which was caused by the change of molecular kinetic mobility during deposition. We found that photoluminescence quenching was stronger in Alq₃ films fabricated at lower substrate temperatures and higher deposition rates. This photoluminescence quenching was not related to molecular orientation and film density and likely originated from the inclusion of impurities in the films. These results indicate that decreasing the amount of impurities in films by increasing substrate temperature or decreasing deposition rate is crucial to achieve the maximum photoluminescence performance from films.