Flexible Organic Light-Emitting Diodes Encapsulated with Gas Barrier Films Prepared by Atomic Layer Deposition

摘要

Various encapsulating films for flexible organic light-emitting diodes (OLEDs) were studied, and gas barrier layers including inorganic Al_2O_3 thin films prepared by atomic layer deposition, organic Parylene C thin films prepared by chemical vapor deposition, and their combination were considered. The transmittance and water vapor transmission rate (WVTR) of the encapsulating films were tested. The effects of various encapsulating films on the luminance and current density of the OLEDs were compared. Lifetime experiments on OLEDs with these encapsulating films were also conducted. The results showed that the transmittance is acceptable even if the polyethylene terephthalate (PET) substrates were coated with two Al_2O_3 and Parylene C layers. The results also indicated the WVTR of the PET substrate was improved by coating the barrier layers. Evaluation of the performance after encapsulation indicates that the OLEDs with Al_2O_3/PET, Parylene C/Al_2O_3/PET (1 pair/PET), and Parylene C/Al_2O_3/Parylene C/Al_2O_3/PET (2 pairs/PET) presented similarly higher luminance compared with the other two cases. Although the 1 pair/PET encapsulation behaved slightly better in terms of luminance than the 2 pair/PET encapsulation, the 2 pairs/PET encapsulation has much longer lifetime. The OLED with 2 pairs/PET encapsulation had nearly double the lifetime compared with the 1 pair encapsulation, and four times compared with the OLED without encapsulation.