A new thin-film encapsulation technology for organic light-emitting devices

Encapsulation is important for organic light-emitting devices (OLEDs) to prevent oxidation of light-emitting materials and electrodes by blocking water vapor and oxygen, and to protect devices from external shocks. A new thin-film encapsulation method is proposed in this work. The film is formed by electron beam evaporation (Al2O3 film) combined with atomic layer deposition (Al2O3 film). We measure the water vapor transmission rate (WVTR) of the film with the method of Ca test. We use the glass substrate, deposit 200 nm film of Ca and 100 nm Al electrode, and encapsulate the entire system with thin-film, leaving only part of the Al electrode as the contact electrode. It is obvious that the oxide-time of Ca of the device encapsulated with electron beam evaporation layer combined with atomic layer is much longer than that of single encapsulation film structures. For further research, we fabricate a set of green OLED devices: ITO/MoOX(5 nm)/m-MTDATA (20 nm)/NPB (30 nm)/Alq (50 nm)/LiF(1 nm)/Al. The devices are encapsulated by the thin film which is mentioned above. The results show that the lifetime of device with thin-film encapsulation is extended than the device without thin-film encapsulation.