Microlens arrays with adjustable aspect ratio fabricated by electrowetting and their application to correlated color temperature tunable light-emitting diodes

Abstract

We develop a facile, fast, and cost-effective method based on the electrowetting effect to fabricate concave microlens arrays (MLA) with a tunable height-to-radius ratio, namely aspect ratio (AR). The electric parameters including voltage and frequency are demonstrated to play an important role in the MLA forming process. With the optimized frequency of 5 Hz, the AR of MLA are tuned from 0.057 to 0.693 for an increasing voltage from 0 V to 180 V. The optical properties of the MLA, including their transmittance and light diffusion capability, are investigated by spectroscopic measurements and ray-tracing simulations. We show that the overall transmittance can be maintained above around 90% over the whole visible range, and that an AR exceeding 0.366 is required to sufficiently broaden the transmitted light angular distribution. These properties enable to apply the developed MLA films to correlated-color-temperature (CCT)-tunable light-emitting-diodes (LEDs) to enhance their angular color uniformity (ACU). Our results show that the ACU of CCT-tunable LEDs is significantly improved while preserving almost the same lumen output, and that the MLA with the highest AR exhibits the best ACU performance.

Direct Microtip Focused Electrohydrodynamic Jet Printing of Tailored Microlens Arrays on PDMS Nanofilm‐Modified Substrate

“…In recent years, microlens arrays (MLAs) have attracted extensive attention due to their wide applications in various fields such as digital displays, [ 1–3 ] light‐emitting‐diodes (LEDs), [ 4,5,6,7 ] super‐resolution imaging, [ 8,9,10 ] and artificial compound eyes. [ 11,12,13 ] The demand of MLAs with precise shaping features has increased over the last few decades.…”

“…In recent years, microlens arrays (MLAs) have attracted extensive attention due to their wide applications in various fields such as digital displays, [1][2][3] light-emitting-diodes (LEDs), [4,5,6,7] super-resolution imaging, [8,9,10] and artificial compound used to fabricate micro/nanolens arrays (M/NLAs). [13,28] Zhou et al reported that the diameters of the MLAs fabricated by E-jet printing decreased from 32.45 to 1.59 µm when the inner diameter of the nozzle decreased from 25 to 1 µm.…”

(Y,Gd)BO₃:Eu red phosphor for dual-layer phosphor structure to enhance the optical performance of white light-emitting diodes

“…A structure of a ring remote phosphor layer that surrounds an inverted cone lens encapsulant was proposed. This structure did enhance the lumen output as it can direct the lights excited from the chip straight to the LED surface, which greatly reduced the amounts of lights lost from the light reflection inside the WLED package [19]- [21]. Another study reported the ability of yielding high angular CCT uniformity and stability of a patterned remote phosphor structure having the surrounding area uncoated with phosphors [22].…”

The application of Ca5B2SiO10:Eu3+ and YAl3B4O12:Ce3+,Mn2+ in dual-layer remote phosphor to enhance lumen output and color quality of WLEDs

“…These days, the conventional light source is not able to meet the requirements of modern applications. Thus, the fourth-generation light source called phosphor-converted white light-emitting diodes (pc-WLEDs) is used as an alternative which can bring better prospects in lighting solutions [1]. Its applications have spread out in many different aspects of human life, including landscape, street lighting, and backlighting.…”