Solution Processed Alternating Organic/Inorganic Multilayer for OLED Encapsulation

Abstract

Organic light-emitting diodes (OLEDs) are promised to replace the existing displays and lightings in terms of the quality of light. One of the most exciting features of organic electronics is that they can be made flexible. However, flexible OLED encapsulation is actually one of the major challenges because they are very sensitive to oxygen and moisture. Thin-film encapsulation (TFE) prepared by vacuum-deposition processes (ALD, CVD) have high barrier properties, but low throughput and high cost. For the significant cost reduction, all solution-processed roll to roll (R2R) production of OLEDs need to be established. Among the technologies needed, that for the thin-film encapsulation (TFE) imposes the highest challenge, because thin films with a very high level of barrier performance needs to be fabricated onto a complete organic device, so that solvents to attack the materials and high temperature treatments need to be strictly avoided. In this work, organic/inorganic multilayer encapsulation structures based on one step solution-processed alternating polysiloxane and silica layer are presented in Fig. 1(A), in which organic layers are spin-coated, followed by polymer crosslinking reaction, and finally subjected to photochemical conversion of the surface into dense silica barrier layers under exposure to vacuum ultraviolet（VUV) light. The whole process is very simple and fast to perform at room temperature, and the coating solution is successfully developed not to destroy the pre-formed organic emitting layer. Transmission electron microscopic (TEM) image shows successful fabrication of multi-stacks of organic/SiOx hybrid alternating layers (Fig. 1(B)). The thickness of ~ 100 nm was achieved per coating. The performance of such multilayer as thin-film encapsulation (TFE) of an OLED device has also been investigated as shown in Fig. 1 (C). The preliminary life time to reach 90% of the initial luminance (5000 cd/m2) was 73 hours for the OLED encapsulated with 450 nm TFE, about 6 times extended compared to that of the bare device. Figure 1