Passivation Properties of UV-Curable Polymer for Organic Light Emitting Diodes

Abstract

We found using UV-curable polymer (NOA63 from Norland Optics) film as a passivation layer, which was very simple and convenient to perform, could provide a temporary barrier for the organic light emitting devices (OLEDs). The NOA63 protective layer significantly restricted the moisture that penetrated into the OLEDs, but did not affect its luminescent characteristics. The decay time of device reaching 70% initial luminance was 1860 min, 6.8 folds longer than that of device without encapsulation. The effective water vapor transmission rate achieved 0.031 g/m 2 /day at 20 • C and 50% relative humidity condition. © 2013 The Electrochemical Society. [DOI: 10.1149/2.007309ssl] All rights reserved. Extensive attention has been paid to organic light-emitting devices (OLEDs) due to their possible use in a wide range of display and lighting applications.1-9 However, the short lifetime is still a critical factor, which greatly limits the industrialization of OLEDs. The organic materials in the light-emitting layer are susceptible to be damaged under air. 4,5 Additionally, the electrode materials may be negatively affected by oxidation. 6,8 In that case, the evolution of "dark spots" was identified as the principal degradation mechanism. Operating OLEDs in air resulted in a vast majority of loss of electroluminescent (EL) intensity in incipient several hours.10 Therefore, there is a significant demand for techniques that are able to preserve device characteristics for air-sensitive devices during fabrication and testing. Especially for laboratory aim, such as shipping incomplete samples and testing, do not often require the extended lifetimes that commercial products demand. In this study, we reported a solution that is accessible to R&D groups to be able to preserve device characteristics during storage and shipping time. The protection layer was UV-curable polymer (NOA63 from Norland Optics) film formed by using a simple spin coating method. This method does not damage the luminescent characteristics of devices, and has no need of any vacuum or heating process and can be potential utilized for elementary encapsulation. Of the OLEDs Experiments NOA63 is a clear, colorless and liquid photopolymer that crosslinked when exposed to ultraviolet light. The solid NOA63 has excellent optical and strong mechanical properties, most commonly used as nanometer-scale contact printing and imprint lithography, 11 or a template-stripping photopolymer substrate. 12 Here, we will propose another NOA63 application as a passivation layer for OLEDs thin film encapsulation (TFE). This TFE method using generally spincoating technology to present a straightforward approach to handling air-sensitive OLEDs for laboratory storage and shipping.To investigate the influence of the NOA63 fabrication process on the Current density-Voltage-Luminance characteristics (I-V-L) of the OLEDs, glass-based small molecular OLEDs were fabricated. As shown in Fig. 1, patterned indium-tin oxide (ITO)-coated glass substrates with the sheet resistance of 10 / was clea...

Interfacial Engineering in Solution Processing of Silicon-Based Hybrid Multilayer for High Performance Thin Film Encapsulation

“…While PDMS/SiO x has a WVTR of 1.5 g/m 2 /day, far too large for a TFE, the values for both PONT coatings were below the detection limit, resulting in an estimated WVTR < 10 –4 g/m 2 /day. Although precise measurement of the WVTR must be done by methods with higher sensitivity and after careful optimization of the PONT structure, the preliminary test already gave a quite promising low WVTR, in fact, the lowest so far reported for solution-processed TFEs to our knowledge. − Also, it is very encouraging that such a high barrier coating could be applied to PET films for FOLED applications.…”

“…The goal of the water vapor transmission rate (WVTR) for a TFE is set at 10 –6 g/m 2 /day to guarantee a minimum OLED lifetime of 10,000 h, while maintaining a total thickness of less than 5 μm to ensure the flexibility of the entire device. , In spite of the tremendous past efforts to look for materials and methods for solution processing of TFEs, the WVTR of even the best examples still stays somewhere around 10 –2 g/m 2 /day. − More importantly than speaking about the choice of the materials for their intrinsic barrier properties, how to fabricate perfectly continuous thin layers without pinholes and cracks becomes the highest challenge, as they provide fast pathways for gases to pass through. , Good adhesion of a hard and brittle inorganic layer to a soft and elastic organic layer is needed to relax strain and avoid formation of cracks. − Since it is almost impossible to achieve a perfect barrier in a single coating even by employing gas phase processing, multiple coatings of alternating stacks were always needed. − …”

Nanometer-Thick SiN Films as Gas Barrier Coatings Densified by Vacuum UV Irradiation

“…Because the barrier performance strongly depends on the film density, and commonly used polymer films contain relatively large free volumes, the WVTRs of encapsulated organic polymer materials are generally high (3–350 g/m 2 /day) . Organic polymer films with relatively high barrier performance have recently been reported. , In addition, several methods for enhancing the organic polymer film barrier performance, such as the embedment of SiO 2 nanoparticles to create a tortuous path and molecular orientation control of polymer molecules, have been reported in the literature. , The WVTRs of the resulting materials were higher than 0.02 g/m 2 /day and could not reach the WVTR of the encapsulated dense inorganic films fabricated following a vacuum process (∼10 –6 g/m 2 /day). , …”

The improvement of thin film barrier performances of organic–inorganic hybrid nanolaminates employing a low-temperature MLD/ALD method

“…OLED degradation due to air-permeation can therefore become a major drawback, which limits their practical utility. 4,5 These limitations are being overcome with the advent of new OLED encapsulation technologies, and signicant research is now focused on the development of thin lm encapsulation (TFE) as one of the most effective ways to solve OLED degradation due to air-permeation. [6][7][8][9][10][11][12][13] Among established TFE technologies, the atomic layer deposition (ALD) technique has been widely reported.…”