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Proceedings Paper

Enhanced color conversion efficiency of remote phosphor-converted light-emitting diodes using micro-concavity arrays
Author(s): Shudong Yu; Junchi Chen; Yong Tang; Zongtao Li; Binhai Yu; Uli Lemmer; Guillaume Gomard
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Paper Abstract

Remote phosphor-converted LEDs (rpc-LEDs), which rely on a phosphor layer located away from the LED chip, are a particularly attractive technology benefitting from a higher luminous efficiency and from an improved stability compared with on-chip LEDs. However, systems based on thin-film remote phosphor layers still face a low color conversion efficiency (CCE). This mostly originates from an insufficient interaction of the exciting blue light with the phosphors. To overcome this limitation, we propose to couple the thin-film converting layers to a micro-concavity array (MCA) designed to enhance the optical pathlength of the exciting light, resulting in an improved CCE. This is achieved by exploiting the excellent light scattering and retro-reflection properties of MCA. We experimentally verify that the MCA transmit 95% of the incoming blue light into the converting layer, whereby 84% of this share corresponds to scattered light. Moreover, the measured retro-reflection amounts to 21% for normally incident light. The potential of the fabricated MCA films is tested by integrating them on the illuminated side of remote light converting thin-film layers with sub-millimeter thickness. Two examples, including quantum dots (QDs)- and rare-earth phosphor- based LEDs, are investigated. Our results show that the CCE of both rpc-LEDs are improved due to the enhanced excitation of the downconverted materials and to the effective extraction of the backscattered light. Thus, the CCE values of QDs-based and phosphor-based and rpc-LEDs are increased by 8.1% and by 12.7%, respectively, compared to devices without MCA films. In the latter case, the angular color uniformity is additionally improved under the effect of light scattering.

Paper Details

Date Published: 22 May 2018
PDF: 11 pages
Proc. SPIE 10687, Organic Electronics and Photonics: Fundamentals and Devices, 106871I (22 May 2018); doi: 10.1117/12.2319151
Show Author Affiliations
Shudong Yu, South China Univ. of Technology (China)
Karlsruher Institut für Technologie (Germany)
Junchi Chen, South China Univ. of Technology (China)
Yong Tang, South China Univ. of Technology (China)
Zongtao Li, South China Univ. of Technology (China)
Foshan Nationstar Optoelectronics Co. Ltd. (China)
Binhai Yu, South China Univ. of Technology (China)
Uli Lemmer, Karlsruher Institut für Technologie (Germany)
Guillaume Gomard, Karlsruher Institut für Technologie (Germany)

Published in SPIE Proceedings Vol. 10687:
Organic Electronics and Photonics: Fundamentals and Devices
Sebastian Reineke; Koen Vandewal, Editor(s)

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