OLED Pixel Shrinkage Dependence with Cathode Influenced by Thermal Effect

In OLED displays, pixel shrinkage due to the operating/storage temperature and aging of the devices is causing serious concern. Here, we report an influence of thermally treated Mg:Ag-based thin-film cathode on the OLED pixel shrinkage. The SEM results show significantly pronounced Ag islands formation in only Ag (16 nm) film, annealed at 100 °C for 24 h. On the other hand, a very clean and continuous film is noticed in the Mg:Ag (5:1, 16 nm) cathode before and after the thermal treatments. To address the shrinkage concern, Mg:Ag (10:1, 16 nm), Mg:Ag (1:10, 16 nm), LiF (1 nm)/Mg:Ag (1:10, 16 nm), and Mg:LiF (1:1, 2 nm)/Mg:Ag (1:10, 16 nm) cathodes are fabricated and stored at 85 °C for 240 h. In the Mg:Ag (10:1, 16nm) film, the optical microscope and SEM images reveal the smooth and continuous film. In contrast, the Mg:Ag (1:10, 16 nm) thin film shows islands formation. The surface morphology is significantly improved in the LiF (1 nm)/Mg:Ag (1:10, 16 nm) cathode. Furthermore, a very clean and continuous film is observed when the Mg:Ag (1:10, 16 nm) cathode is deposited on the Mg:LiF (1:1, 2 nm) film. The phosphorescent red TEOLED fabricated using the Mg:LiF (1:1, 2 nm)/Mg:Ag (1:10, 16 nm) cathode shows improved operational performances.