Abstract
Color-converted micro-light-emitting diode (micro-LED) displays with wide color gamut, high ambient contrast ratio, and fast response time are emerging as a potentially disruptive technology. However, due to limited optical density and thickness of the color-conversion film, the blue light leakage and low color-conversion efficiency still hinder their widespread applications. In this paper, we demonstrate a patterned cholesteric liquid crystal (CLC) polymer film with two special optical functionalities. On the green and red sub-pixels, the corresponding planar CLC texture acts as a distributed Bragg reflector for the blue light, which in turn improves the color conversion efficiency and expands the color gamut. On the blue sub-pixels, the corresponding focal-conic CLC texture acts as light scattering medium, which helps to reduce the angular color shift. Further analysis reveals that the patterned CLC film can alleviate the crosstalk between green and blue color filters. Therefore, compared to the display system without such a CLC film, our proposed device structure increases the color conversion efficiency by 143% (at ~90% Rec. 2020) and reduces average angular color shift Δu’v’ from 0.03 to 0.018 at the viewing angle with the most severe color shift. Such a patterned CLC film is applicable to all kinds of color-conversion display systems, including organic and inorganic phosphors.
Highlights
Micro-light-emitting diodes have begun to emerge as a potentially disruptive display technology, provided that their cost can be reduced significantly [1,2]
We evaluate the improvement of our proposed patterned cholesteric liquid crystal (CLC) film system versus the control system in three aspects: (1) color conversion efficiency, (2) color gamut, and (3) viewing angle
We proposed to employ a high-transmittance color filter (CF1) with a wide band CLC film (WB-CLC film)
Summary
Micro-light-emitting diodes (micro-LED) (with a chip size less than 100 μm) have begun to emerge as a potentially disruptive display technology, provided that their cost can be reduced significantly [1,2]. Due to the complex manufacturing process (mass transfer technology) and driving circuit design (pulse width modulation), the cost of RGB micro-LED displays remains relatively high at the present time. To overcome these problems, a simpler method has been proposed that could achieve full color by assembling a blue micro-LED array with a color conversion layer [5,6,7]. In order to obtain a high performance micro-LED display with wide color gamut, high color conversion efficiency (CCE) and large viewing angle, the following three main obstacles should be overcome: (1) blue light leakage of the red and green sub-pixels. The angular spectrum mismatch from the RGB sub-pixels may cause a significant angular color shift [13,14]
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