Tris(8-hydroxyquinoline)aluminium in a polymer matrix as an active layer for green OLED applications

Tris(8-hydroxyquinoline)aluminium with poly(N-vinylcarbazole) (Alq3:PVK) or polystyrene sulfonate (Alq3:PSS) were deposited by spin-coating on glass and silicon substrates. SEM measurements show that relatively smooth thin films were obtained. Fourier transform infrared measurements were performed to confirm the composition of the samples. The optical properties of thin films containing Alq3:PVK and Alq3:PSS were characterised using absorption spectroscopy and spectroscopic ellipsometry. It was found that the absorption spectrum of Alq3:PVK is characterised by four bands, while for Alq3:PSS only three bands are visible. The photoluminescence of the studied thin layers shows a peak with a maximum at about 500 nm. Additionally, cyclic voltammetry of Alq3 is also presented. Theoretical density functional theory calculations provide the insight into the interaction and nature of Alq3:PVK and Alq3:PSS excited states. Finally, the organic light-emitting diode (OLED) structure based on Alq3:PVK was fabricated and showed strong electro-luminescence with a green emission at 520 nm. The results of the device show that the ITO/PEDOT:PSS/Alq3:PVK/Ca/Al system can be useful for the production of low-cost OLEDs with Alq3:PVK as an active layer for future lighting applications.