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Nucleation and Growth of Optically Efficient Organic Nano-lens Arrays Fabricated by a Vacuum Deposition
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- Authors
- Young-Sam Park, Doo-Hee Cho, Sunwook Kim, Minjong Keum
- Issue Date
- 2020-09
- Citation
- Thin Solid Films, v.709, pp.1-5
- ISSN
- 0040-6090
- Publisher
- Elsevier
- Language
- English
- Type
- Journal Article
- Abstract
- There are few techniques applicable to top-emitting organic light emitting diode (TOLED) panels, as organic films are easily deteriorated by heat stress, oxygen and moisture exposure when a light extraction structure is fabricated on top of TOLEDs. Recently, we have reported that a N??-Di(1-naphthyl)-N,N??-diphenyl-(1,1??-biphenyl)-4,4?쾑iamine nano-lens array (NLA) fabricated by using a simple and highly process-compatible vacuum deposition works as an optically efficient structure when NLA with a lens size of several hundred nanometers is deposited on the oxide layer of the TOLED. To achieve the desirable optical properties of TOLEDs, the vacuum NLA process was controlled to obtain big nano-lenses with a diameter of several hundred nanometers, indicating the importance of understanding of the nucleation and growth behavior of NLA. Here, the systematic NLA experiments using glass and alumina substrates indicate that nano-lenses are formed by nucleation and growth of nuclei. Very interestingly, the nucleation is completed in the early stage of the deposition process, followed by growth without decreasing the total number of nano-lenses per area, and finally followed by growth with decreasing the total number due to Ostwald ripening. Compared to alumina substrates, smaller sizes and greater rates of nucleation of NLAs in glass substrates are explained by the difference in substrate surface energy combined with a classical thermodynamic theory using the difference in Gibbs free energy.
- KSP Keywords
- Alumina substrate, Extraction structure, Gibbs Free Energy, Glass substrate, Growth behavior, Heat Stress, Lens array, Moisture exposure, Organic light-emitting diodes(OLEDS), Oxide layer, Thermodynamic theory