Manufacturing And Reliability Research Of White Organic Light-emitting Diode Based On Thin Film Encapsulation

Organic light-emitting diodes (OLEDs) are currently under intense investigation because of their advantages such as excellent image quality, light weight, easy manufacturability, low cost and large-area extendibility. The potential industrial application of OLEDs to large area panel full-color displays and flexible organic electroluminescent displays has been limited by short operation lifetime due to the sensitivity to water vapor and oxygen. Effective encapsulation technologies especially the method which can be applied to flexible display and top-emitting OLEDs have not been fully resolved yet, which hindered the large-scale OLEDs’marketing.In this dissertation we utilize multilayer organic light-emitting diodes with a thin layer of dye molecules to study the mechanism of charge trapping under different electric regimes. It demonstrates that the carrier trapping was independent of the current density in devices using fluorescent material as the emitting molecule while this process was exactly opposite when phosphorescent material was used. The triplet–triplet annihilation and dissociation of excitons into free charge carriers was considered to contribute to the decrease in phosphorescent emission under high electric fields. Moreover, the fluorescent dye molecule with a lower energy gap and ionized potential than the host emitter was observed to facilitate the carrier trapping mechanism, and it would produce photon emission.We report highly efficient gas diffusion barriers for organic light emitting diodes with an encapsulation structure composed of alternating magnesium fluoride (MgF2) and zinc sulfide (ZnS) layers grown by vacuum thermal deposition. The half lifetime of yellow OLEDs under an initial luminance of 2000 cd/m2 with rubrene as an emitter reached 245 h using three pairs of MgF2/ZnS layers. The device lifetime was obviously improved using MgF2 and ZnS as passivation layers before UV-cured epoxy seal without desiccant with the lifetime for the initial luminance dropping to 56% being over 500 h. This simple and inexpensive encapsulation method can potentially be applied to top-emitting OLEDs due to good light transmission characteristic of the passivation film.Color conversion method has been used to fabricate chromatic-stability white organic light-emitting diodes (OLEDs). Experimental results found little CIE coordinate migration while changing operation voltage from 5 V to 12 V. A simple thin-film encapsulation (TFE) structure has been developed through vacuum thermal deposition in combination with plasma enhanced chemical vapor deposition. The luminance of the encapsulated white OLED remain unchanged during the test time. The novel approach is being expected to lower the cost and achieve high-performance TFE.