Design considerations for highly efficient edge‐lit quantum dot displays

Abstract

Quantum Dots (QDs) are increasingly the technology of choice for wide color gamut displays. Two popular options to incorporate QDs into displays include on-edge and on-surface solutions. The opto-mechanical design for an on-edge QD solution is more complex than the design for a standard white phosphor LED light bar. In this paper, we identify and investigate a range of design parameters for an on-edge QD light bar, and we show that these parameters have significant influence on system efficiency and color uniformity. The effects of varying these parameters are explored through the use of a custom adjustable testbed and optical raytracing methods. Our testbed data demonstrate the inherent tradeoffs between efficiency and color uniformity and provide guidance for the design of high performing displays. The optical raytracing data demonstrate a good predictive capability and support the use of optical modeling methods for a detailed exploration of a wider range of design parameters. Author Keywordsquantum dot; wide color gamut; edge optic; backlight unit; optical raytracing. Objectives and BackgroundA current major trend in display technology is towards wide color gamut [1][2]. Wide gamut displays provide more highly saturated colors which appear brighter than less saturated colors at the same luminance [1]. Multiple studies have suggested that higher gamut content receives increased attention [3][4]. Highly accurate color representation is required for viewing of native DCI and Adobe RGB content, as well as the production of true ultra high definition and cinema quality displays. Narrow bandwidth emitters with adjustable peak emissions that are aligned with the LCD color filter transmittance enable a wide gamut with high efficiency. Quantum Dot (QD) technology, in which QDs downconvert absorbed radiation into a lower frequency emission, effectively fills this need [5][6]. A peak wavelength emission that is highly tunable to ± 1 nm by selection of particle size, with a full width half maximum bandwidth that is 30 nm or less and a quantum yield that is in excess of 90% is desirable. In a typical display usage, blue excitation light from GaN LEDs is downconverted by QDs to green and red light. The combination of blue excitation light and QD-generated green and red light gives white light with distinct, narrow spectral peaks. QD based backlight units (BLUs) can be produced at a price point similar to that of the standard white LED BLUs, which have a substantially lower gamut. Mass production of QDs and integration into existing backlight manufacturing processes have been demonstrated in commercially available displays, including Sony Triluminos TVs, Hisense TVs, TCL TVs, and Philips TVs and monitors.Options for incorporating QDs into a BLU include on-edge, onsurface (e.g., film), and on-chip (e.g., direct lit) configurations. This paper considers the on-edge solution, in which a glass tube containing red and green emitting QDs is located along one or more edges of the BLU between the blue LED light bar and the ...

Mini-LED Backlight Technology Progress for Liquid Crystal Display

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