CaF₂/ZnS Multilayered Films on Top-Emission Organic Light-Emitting Diode for Improving Color Purity and Moderation of Dark-Spot Formation

Abstract

Organic light-emitting diodes (OLEDs) have been widely used, particularly in display applications. OLEDs are easily degraded without stringent encapsulation owing to their susceptibility to water vapor and oxygen. Therefore, establishing an effective protection method for these devices is essential. In this study, we demonstrate the device protection performance and improvement in color purity by introducing CaF 2 /ZnS multilayered films on a top-emitting inverted-type OLED (iOLED), which was originally intended to act as a distributed Bragg reflector (DBR). To test the protection performance of each dielectric layer, conventional bottom-emitting OLEDs (cOLEDs) with and without single layers of CaF 2 and ZnS were investigated for comparison. All OLEDs were stored in an atmosphere without stringent encapsulation, such as a cover glass. The luminescence area of cOLEDs without the dielectric film decreased by more than 90% after 3 days of fabrication. In contrast, the dark-spot formation was moderated after the same period for the dielectric single-layer deposited cOLEDs. Notably, the iOLED with DBR completely preserved the emitting area even after 2 months of fabrication. This suggests that DBR acted as a protective film for the organic layer, whereas the inverted structure also contributed to reducing the degradation of air- and moisture-sensitive materials.

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