Reliable high temperature, high humidity flexible thin film encapsulation using Al 2 O 3 /MgO nanolaminates for flexible
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Reliable high temperature, high humidity flexible thin film encapsulation using Al2O3/MgO nanolaminates for flexible OLEDs Ki Suk Kang1, So Yeong Jeong1, Eun Gyo Jeong2 (), and Kyung Cheol Choi1 () 1
School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea 2 Department of Clothing and Textiles, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186, Republic of Korea © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 22 March 2020 / Revised: 2 June 2020 / Accepted: 4 June 2020
ABSTRACT Since most organic materials are very sensitive to moisture and oxygen, organic light emitting diodes (OLEDs) require an encapsulation layer to protect the active layer from these gases. Since light, flexible and portable OLEDs are being employed in more diverse climates and environmental conditions, the OLED encapsulation layer must retain robust mechanical properties and stability in high temperature/high humidity conditions. Al2O3 films have demonstrated excellent barrier performance, but they readily hydrolyze when exposed to prolonged harsh environments. In this study, we fabricated a thin film encapsulation (TFE) film that was resistant to hydrolysis, using Al2O3/MgO (AM) nanolaminates. MgO has superior resistance to harsh environments, and the aluminate phase generated by the chemical reaction of Al2O3 and MgO provided excellent barrier performance, even after storage in harsh conditions. A multi-barrier fabricated using the AM nanolaminate showed excellent barrier performance, close to the level required by OLEDs. It did not significantly deteriorate even after a bending test of 1,000 iterations at 0.63% strain. After 1,000 cycle of bending, the electrical properties of the passivated OLEDs were not significantly degraded at shelf-lifetime test where the fabricated device was stored for 50 days in a harsh environment of 60 °C, 90% relative humidity. The multi-barrier shows the best performance compared to previous studies on flexible encapsulation that can be used in harsh environments.
KEYWORDS thin film encapsulation, nanolaminate structure, Al2O3, MgO, flexible, organic light emitting diode (OLED)
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Introduction
Increasing demand for flexible display devices is driving considerable interest and research in organic light emitting diodes (OLEDs), which are the most promising candidates for the application, despite their sensitivity to moisture and oxygen [1–3]. Encapsulation technologies are considered one of the best methods of protecting OLED devices from environmental degradation by moisture and oxygen. Recently, in addition to the conventional fragile glass-lid encapsulation approach [4–6], thin film encapsulation (TFE) is being investigated as an effective protection method for flexible OLEDs. This is largely because TFEs can prevent edge-permeation [7] and provide much greater flexibility than conventional encapsulation techniques. Several types of TFE te
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