This Letter proposes the use of atomic layer deposition (ALD) encapsulation as a stability-improving approach for a quantum-dot micro-structural array (QDMA) with a random rough interface. The QDMA is first prepared by screen printing technology on an edge-lit light-guide plate (LGP) for backlight application. A flexible aluminum oxide film is then densely deposited onto the rough surface of the QDMA. The influences of two key factors, the reaction temperature and deposition thickness, on the encapsulation effect and output performance of this QD backlight are discussed. After ALD encapsulation, the water vapor transmission rate was measured to be less than 0.014 g/(m2 day). The average luminance of the encapsulated QD backlight remained stable after continuous working for 200 h, while an unencapsulated QD backlight lost over 50% of its initial luminance. The complete attenuation trend for the encapsulated QD backlight was analyzed in a more demanding testing environment, and results showed that 80% (>3000 cd/m2) of the initial luminance was maintained after 250 h at a high temperature of 70 °C and a relative humidity of 90%. The mechanism behind these experimental results is also discussed.
Pixelated quantum-dot color conversion film (QDCCF) is attractive for next-generation, high-pixel-density, full-color displays. However, how to achieve white balance of these QD converted displays puts forward a new challenge, because the final light-emitting area is redefined by the apertures of the QD formed subpixels. Based on this, this paper presents an effective white-balance realization approach by precisely defining an asymmetric aperture ratio among three primary-color subpixels of the QDCCF. Based on the measured photoluminescence characteristic of quantum-dot photoresist (QDPR), the theoretical aperture ratio can be derived by the spectral radiation energy and external quantum efficiency (EQE) of QDCCFs for the target D65 white-balance state. A bilayered device architecture, combining a blue mini-LED backlight and a pixelated QDCCF, was simulated and experimentally assembled to verify the theoretical design. The simulated chromatic coordinates obtained from the QDCCF precisely agree with the target white-balance point. Experimental patterning and pixelation of the designed QDCCF were achieved by a precise photolithography process. Measured results show that a white-light output was achieved with the chromatic coordinates of (0.2822, 0.2951) and the color gamut of 115.09% NTSC (National Television System Committee) standard. The deviation of the experimental chromatic coordinates is within ±0.05 to the D65 standard light source. The proposed white-balance realization approach featured by the aperture adjustable subpixels of a chromatic QDCCF may open up a new route for color reproduction in emerging display technologies.
Microcontact printing (CP) was used in conjunction with self-assembled monolayers (SAMs) of hexadecanethiolates to fabricate gold etch masks on GaAs and GaAs/AlGaAs quantum-well substrates; patterns in the mask were transferred into the semiconductor with an anisotropic dry chemical-etch process. The measured luminescence efficiency of the etched features in GaAs/AlGaAs was similar to that of samples patterned using conventional lithography; this observation indicates that no mechanical or chemical damage is incurred in the CP process.
Quantum-dot color conversion (QDCC) is a promising technique for next-generation full-color displays, such as QD converted organic light-emitting diodes and micro light-emitting diodes. Although present QDCC research has made some progress on the experimental aspect, the optical model and corresponding mathematical expression that can lay an indispensable foundation for QDCC have not been reported yet. In this paper, we present a theoretical model for precisely describing the complete optical behavior of QDCC, including optical transmission, scattering, absorption, and conversion process. A key parameter of QDCC, called dosage factor (DoF), is defined to quantitatively express the total consumption of QDs that can be calculated as the product of film thickness and QD concentration. Theoretical relations are established between DoF and three key performance indicators of QDCC, namely the light conversion efficiency (LCE), blue light transmittance (BLT), and optical density (OD). The maximum LCE value can be predicted based on this theoretical model, as well as the relationship between the slope of the OD curve and the molar absorption coefficient of blue light. This theoretical model is verified by both simulation and experiment. Results show that the simulation and experimental data highly match the theoretical model, and the goodness of fit reaches higher than 96% for LCE, BLT, and OD. Based on this, the optimal interval of DoF is recommended that provides key guiding significance to the QDCC related experiment.
The performances of quantum-dot (QD) based photoluminescent devices are highly restricted by the application environment, especially the moisture and oxygen. However, current external encapsulation structures are not applicable to the devices with discrete QD distribution, especially for some rough profiles. To address this issue, an encapsulation method for discretely distributed quantum-dot arrays (DQDA) is proposed for liquid crystal display (LCD) backlight applications, in which the DQDA can be well fabricated by printing the QD slurry onto a light guiding substrate (LGS), and then covered with a thin UV glue layer and a barrier film. By specially optimizing the UV glue and barrier film, this ultra-thin encapsulation structure cannot only improve the surface defects of the QD morphology without affecting the original light path and the output optical performance, but also significantly suppress the fluorescence decay and isolate moisture and oxygen by almost 100 times compared with unencapsulated one. The water vapor transmission rate (WVTR) was measured to be 1.29 × 10 −4 g/m 2 /day after fabricated the stacked encapsulation structure. After a long period of aging test, the encapsulated sample kept its luminance for 1000 hours. This method also has potential to widely used for discrete structures in other device applications due to its easy fabrication process, high reliability, and low manufacturing costs.
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