A Systematic Study of the Interactions in the Top Electrode/Capping Layer/Thin Film Encapsulation of Transparent OLEDs
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INTRODUCTION
Flexible transparent organic light-emitting devices (TOLEDs) and top-emitting organic light-emitting diodes (TEOLEDs) have attracted increasing interest for use in next-generation displays [1], [2], [3]. In these OLED devices, the transparent top electrode still requires many improvements, and significant research efforts have been devoted to its development. Generally, top electrode materials are composed of transparent conducting oxides (TCOs) or thin metal films as well as combinations of
Fabrication of TOLEDs with both Al2O3 TFE and various CL layers
Fig. 1 shows a schematic of the TOLED structure. The TOLEDs containing N, N′‐diphenyl‐N, N′‐bis [1‐naphthyl‐(1, 1′‐biphenyl]‐4, 4′‐diamine (NPB), 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HATCN), and tris (8‐hydroxyquinoline) aluminum (Alq3) CLs were fabricated with the following structure: glass as a substrate/ITO (70 nm) as an anode/HATCN as a hole injection layer (HIL) (10 nm)/NPB (40 nm) as a hole transport layer (HTL)/ 4,4′,4″-tris(Ncarbazolyl)-triphenylamine (TcTa) (10 nm) as an
RESULTS AND DISCUSSION
As shown in Fig. 1, a transparent conducting electrode with low reflection and absorption, a CL acting as refractive index-matching, and a TFE with high water vapor barrier properties are all critical individual components of TOLEDs. By using a low-temperature (95 °C) thermal ALD process for the encapsulation of the TOLEDs, this allows for detailed and systemic studies related to top electrodes, CLs, TFE, and their interfaces of electro-optically controlled TOLEDs.
Fig. 2(a)–(c) show the
CONCLUSION
Herein, TOLEDs with both Al2O3 TFE and various CL layers were fabricated. The top electrode (thin Ag), CLs (NPB, HATCN, and Alq3), TFE (Al2O3), and their interfaces were studied using various characterization techniques. The CLs exhibited different surface properties: The NPB and Alq3 formed hydrophobic surfaces with water contact angles of 97.65° and 64.62°, but the HATCN formed a hydrophilic surface with a water contact angle of 48.53°. However, the Al2O3 film density grown on the CLs with
Declaration of interest statement
None declared.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgement
This work was partly supported by Electronics and Telecommunications Research Institute (ETRI) grant funded by the Korea government [20ZB1100, Development of Creative Technology for ICT] and an Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIT) [2018-0-00202, Development of core technologies for transparent flexible display integrated biometric recognition device], and an Institute for Information & Communications Technology
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