1
|
Cho DH, Park YS, Choi S, Cho H, Kwon BH, Shin JW, Cho NS. Luminance enhancement of top-emitting blue organic light emitting diodes encapsulated with silicon nitride thin films by a double-layer nano-structure. OPTICS EXPRESS 2022; 30:11959-11972. [PMID: 35473127 DOI: 10.1364/oe.452954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 03/10/2022] [Indexed: 06/14/2023]
Abstract
Even though it is in high demand to introduce a nano-structure (NS) light extraction technology on a silicon nitride to be used as a thin film encapsulation material for an organic light-emitting diode (OLED), only an industry-incompatible wet method has been reported. This work demonstrates a double-layer NS fabrication on the silicon nitride using a two-step organic vapor phase deposition (OVPD) of an industry-compatible dry process. The NS showed a wrinkle-like shape caused by coalescence of the nano-lenses. The NS integrated top-emitting OLED revealed 40 percent enhancement of current efficiency and improvement of the luminance distribution and color change according to viewing angle.
Collapse
|
2
|
Manley P, Walde S, Hagedorn S, Hammerschmidt M, Burger S, Becker C. Nanopatterned sapphire substrates in deep-UV LEDs: is there an optical benefit? OPTICS EXPRESS 2020; 28:3619-3635. [PMID: 32122027 DOI: 10.1364/oe.379438] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 01/15/2020] [Indexed: 06/10/2023]
Abstract
Light emitting diodes (LEDs) in the deep ultra-violet (DUV) offer new perspectives for multiple applications ranging from 3D printing to sterilization. However, insufficient light extraction severely limits their efficiency. Nanostructured sapphire substrates in aluminum nitride based LED devices have recently shown to improve crystal growth properties, while their impact on light extraction has not been fully verified. We present a model for understanding the impact of nanostructures on the light extraction capability of DUV-LEDs. The model assumes an isotropic light source in the semiconductor layer stack and combines rigorously computed scattering matrices with a multilayer solver. We find that the optical benefit of using a nanopatterned as opposed to a planar sapphire substrate to be negligible, if parasitic absorption in the p-side of the LED is dominant. If losses in the p-side are reduced to 20%, then for a wavelength of 265 nm an increase of light extraction efficiency from 7.8% to 25.0% is possible due to nanostructuring. We introduce a concept using a diffuse ('Lambertian') reflector as p-contact, further increasing the light extraction efficiency to 34.2%. The results underline that transparent p-sides and reflective p-contacts in DUV-LEDs are indispensable for enhanced light extraction regardless of the interface texture between semiconductor and sapphire substrate. The optical design guidelines presented in this study will accelerate the development of high-efficiency DUV-LEDs. The model can be extended to other multilayer opto-electronic nanostructured devices such as photovoltaics or photodetectors.
Collapse
|
3
|
Alqurashi T, Penchev P, Yetisen AK, Sabouri A, Ameen RM, Dimov S, Butt H. Femtosecond laser directed fabrication of optical diffusers. RSC Adv 2017; 7:18019-18023. [PMID: 30174826 PMCID: PMC6112377 DOI: 10.1039/c7ra00109f] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/07/2017] [Indexed: 11/21/2022] Open
Abstract
Optical diffusers are widely used in filament lamps, imaging systems, display technologies, lasers, and Light Emitting Diodes (LEDs). Here, a method for the fabrication of optical diffusers through femtosecond laser machining is demonstrated. Float glass surfaces were ablated with femtosecond laser light to form nanoscale ripples with dimensions comparable to the wavelength of visible light. These structures produce highly efficient and wide field of view diffusers. The machined patterns altered the average surface roughness, with the majority of particles in the range of a few hundred nanometers. The optical diffusion characteristic and a maximum diffusion angle of near 172° was achieved with optimum machining parameters. The transmission performance of the diffusers was measured to be ∼30% across the visible spectrum. The demonstrated technique has potential for producing low-cost large area optical devices. The process benefits from the flexibility of the laser writing method and enables the production of custom optical diffusers.
Collapse
Affiliation(s)
- Tawfiq Alqurashi
- Nanotechnology Laboratory, School of Engineering, University of Birmingham, Birmingham, B15 2TT, UK. ; Tel: +44(0) 1214158623
- Department of Mechanical Engineering, School of Engineering, Shaqra University, Dawadmi, Saudi Arabia.
| | - Pavel Penchev
- Nanotechnology Laboratory, School of Engineering, University of Birmingham, Birmingham, B15 2TT, UK. ; Tel: +44(0) 1214158623
| | - Ali K Yetisen
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Aydin Sabouri
- Nanotechnology Laboratory, School of Engineering, University of Birmingham, Birmingham, B15 2TT, UK. ; Tel: +44(0) 1214158623
| | - Rayan M Ameen
- School of Metallurgy and Materials, University of Birmingham, Birmingham, B15 2TT, UK
| | - Stefan Dimov
- Nanotechnology Laboratory, School of Engineering, University of Birmingham, Birmingham, B15 2TT, UK. ; Tel: +44(0) 1214158623
| | - Haider Butt
- Nanotechnology Laboratory, School of Engineering, University of Birmingham, Birmingham, B15 2TT, UK. ; Tel: +44(0) 1214158623
| |
Collapse
|