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Quantum dots (QDs) have been considered next-generation display fluorescent conversion materials due to their excellent color purity and photoluminescence quantum yield. In order to integrate QD with Micro/Mini-LED and other microdevices efficiently, it is necessary to fabricate micro-scale QD pixel arrays. Photolithography is an effective method for fine pattern processing, but conventional photolithographic procedures need to compound QD with a photosensitive curing matrix, which is not conducive to obtaining high color purity QD pixels. Therefore, a QD self-assembly strategy based on a hydrophobic-hydrophilic transformation substrate is proposed, combining ultraviolet (UV) mask exposure and surface charge modification technology to manufacture a high-purity QD pixel array. In this paper, the hydrophobic-hydrophilic transformation substrate is prepared by polyvinylidene fluoride (PVDF)/TiO2 hybrid fibrous membrane substrate. By changing the thickness of the substrate and analyzing its threshold of the photocatalysis time and pattern accuracy combined with the transmittance after encapsulation, the optimal substrate thickness is about 30 um. On this basis, the surface charge of the fibrous membrane is further modified by poly(diallyldimethylammonium chloride) (PDDA) to enhance the self-assembly performance of the QD in the hydrophilic region. The dimensional accuracy and optical characteristic of the QD pixel array have been studied in detail. The color average degree is 96.4%, the consistency is 94.5%, and the dimensional accuracy error is 5.2%. The spectrum of the QD pixel is almost the same as the QD solution, and the transmittance of the films is up to 88.8% under the visible light wave band, which has excellent optical performance. Therefore, this strategy is beneficial for efficiently manufacturing the high-purity QD pixel array, which has a broad application prospect in the high-resolution display field of Micro/Mini light-emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

In this study, we propose a centrifugation packaging (CP) structure to enhance the optical and thermal dissipation performance of LEDs, using SBA-15 particles to facilitate the sedimentation and dispersion of QDs. The results indicate that the EL spectra of the LEDs remains almost unchanged after the centrifugation time of 60 min and a CP structure can be obtained. The radiation power and luminous flux of LEDs with a CP structure improve by 9.1% and 10.4%, respectively, compared with the uniform distribution (UD) structure. The surface temperature of LED devices with the CP structure is reduced to 34.4 °C from 41.8 °C at a current of 100 mA. Furthermore, the simulation results show that the maximum temperature in the CP structure is 22.4% lower than that in the UD structure at a current of 500 mA. Thus, this study can provide a new perspective for designing settlement structures of QD–LEDs to enhance their optical and thermal performance. [ABSTRACT FROM AUTHOR]

Ultraviolet light-emitting diodes (UVLEDs) used as excitation sources for quantum dots (QDs) are promising candidates for the display field. To eliminate the residual excitation light, the conventional method is simply increasing the optical density of QDs for packaging, which would significantly reduce the luminous efficiency of QD-light-emitting diode (LED) devices owing to reabsorption loss. In this study, the combination strategy of a boron nitride (BN) reflective coating and an ultraviolet-reflection filter (UV-R filter) for QD-LED devices is proposed. By managing the recycle of UV light to excite more QDs and reducing the reabsorption effect of QDs carefully, their green emission intensity of LED using such a strategy is 82.0% higher than that of a conventional device with a similar QD light energy proportion of ~99.0% (almost no residual UV excitation light). This strategy is also effective for red QD-LED devices while eliminating residual UV excitation light and enhancing the red emission intensity. Therefore, this study provides an effective way to develop QD-LED devices with high QD emission intensity and low UV light leakage for display. [ABSTRACT FROM AUTHOR]

Near-ultraviolet light-emitting diodes (NUV-LEDs) are more likely to be commercially fabricated. The improvement of their wall-plug efficiency (WPE) by facial and effective methods has made a great impact. We propose a highly reflective boron nitride silicone (BN/silicone) layer to improve the light output power for NUV-LEDs. Our results show that increasing the BN concentration contributes to a higher UV-reflectivity of the BN/silicone layers. When the BN concentration increases from 0.5 to 15 wt%, the light output power enhancement increases gradually, thus achieving a maximum light output power enhancement of 46.2% for NUV-LEDs at a driving current of 350 mA compared with pure silicone encapsulation devices. This significant improvement is attributed to the increased UV-reflectance by the polymer-based lead-frame and packaging materials. Furthermore, the emission angle is decreased by 7.8° at a BN concentration of 15 wt% at 350 mA owing to the strong scattering ability of the BN/silicone layer. This provides more concentrated energy in lighting applications. [ABSTRACT FROM AUTHOR]

Even though chip-on-board light-emitting diodes (COB LEDs) with quantum dots (QDs) are attracting much attention for their high optical performance, their luminous efficiency (LE) is still low owing to total internal reflection. To overcome this problem, in this study, a microfiber-silicone hybrid (MFSH) structure is proposed to enhance the LE of QD-based COB LEDs. Polystyrene (PS) fiber films were fabricated by electrospinning and subjected to planar compression modeling to precisely control their film thickness. Subsequently, these films were coated with silicone to finish packaging the COB LEDs. Their diffuse reflectance of the MFSH structures before and after silicone resin encapsulation was analyzed, witnessing a diffuse reflectance at 450 nm of 97.7% when the pure fiber-film thickness increases to 220~μm. While applying to COB LEDs, the light output power of devices with MFSH structure increases first and then decreases, causing by the balance of light extraction by the scattering fiber and absorption by the difference between chip height and fiber film thickness. Finally, to increase the light-extraction capacity of COB LEDs, the thickness of the microfiber films was optimized to 25~μm at which their LE increased by 29.7% and 31.7% for the blue LED source and QD-based COB LED source, respectively. Therefore, the MFSH structure is an effective packaging method to produce highly efficient COB LEDs. [ABSTRACT FROM AUTHOR]

Chip-scaled package light-emitting diodes (CSP LEDs) are promising for illumination applications because of their advantages of compact size and high luminous density. Contrary to traditional conformal package structures, the material and thickness of top and sides, respectively, are controllable, showing great potential to achieve high color uniformity. In this letter, different kinds of CSP LEDs were comprehensively compared, and the requirements to gain high color uniformity were further investigated with simulation and experiment. Results show that a top volume proportion of phosphor ${V}_{\mathrm {top}}$ between 75% and 85% contributes to high color uniformity for the universally used 35 and 45 mil flip chips. The fabricated CSP LEDs with $V_{\mathrm {top}}=77.8\% $ can gain an extra uniform color distribution with a $\Delta $ CCT of only 92 K at a CCT of approximately 6000 K, which is 82.1% lower than that of traditional conformal LEDs. These results indicate that the CSP structure is an important alternative for illumination applications requiring high color uniformity. [ABSTRACT FROM AUTHOR]

Although multichip light-emitting diode (LED) modules are becoming popular in high-power lighting applications, better light extraction efficiency is always desirable in the industry. In this paper, V-grooves fabricated by the low-cost dicing process have been utilized on the top face of the multichip LED module to enhance the output power. An analytical model including the consideration of surface has been established by using a fractal theory. The combined finite difference time domain and ray tracing method has been used to simulate the light extraction enhancement considering the surface roughness scattering effects. The results show 12% enhancements in the experiments when the measured surface roughness of the V-groove has RMS roughness of 0.25~\mu \textm , which is in good agreement with the simulation result of 13.7%. The multichip LED models have been applied in indoor downlight systems and it is found that the luminous efficiency has been enhanced by 9.6% under a current of 350 mA (5.8 W) when compared with multichip LED modules without V-grooves. [ABSTRACT FROM AUTHOR]