Novel and Highly Efficient White Light-Emitting Devices
|關鍵字:||白光發光二極體;螢光粉;量子點螢光粉;封裝;光電元件;White Light-Emitting Diodes;Phosphor;Quantum Dot Phosphor;Package;Electro-optical devices|
於第二部分研究敘述如何利用硒化鎘/硫化鋅(CdSe/ZnS)量子點材料發展高均勻性量子點單色與白光光源，為提高均勻性與顏色之間區別性，利用脈衝噴塗技術噴塗紅綠藍三色量子點並且結合紫外光發光二極體，成功製作紅綠藍像素陣列圖形與白光發光光源。利用高穿透率的聚甲基矽氧烷(polydimethylsiloxane; PDMS)薄膜作為中間隔層，分隔量子點以提高顏色區別性且降低量子點自聚集效應，此方式可大幅減少各顏色之間相互汙染問題。此外，為提高發光效率，搭配布拉格反射結構(Distributed Bragg Reflector; DBR)，增加紫外光之反射，提高紅綠藍三色量子點亮度。而透過紅、綠、藍量子點所製作的白光背光模組可以大幅的拓寬顯示器的色域，使色域達到NTSC 135 %之高飽和度表現。此外，本研究結合polyfluoren (PFO) 高分子與量子點成為混合型量子點光源，不僅可提高量子點白光光源之發光效率，也可成功製備不同色溫之高品質白光光源。
Recently, white light-emitting diodes (LEDs) have been regarded as the next generation of lighting sources because of its long lifetime, high efficiency, and energy-saving properties, especially in solid-state lighting (SSL). The most basic and common method for producing white light is combining blue LEDs with yellow phosphor (Y3Al5O12:Ce3+) in the package. Although this strategy is widely used in the industry application, developing high luminous efficiency and superior uniformity of angular-dependent correlated color temperature (CCT) white LED simultaneously is the primary issue for phosphor-based LEDs. This behavior strongly limits the development of many specific applications which requires the high quality GaN-based LEDs. In the first part of this study, we propose several methods to enhance the light output and improve the uniformity of lighting. First of all, a dual-layer remote phosphor structure is demonstrated to yield a higher luminous efficiency of WLEDs. Inserting a thin silicone layer into the phosphor layer and optimizing the ratio of the different layers increased transmission, thereby increasing light output. Next, a hybrid phosphor structure is developed to produce highly uniform white LED by using the pulse spray and dispensing methods. This improvement occurred because the blue light divergent angle in the hybrid structure was larger than in the dispense structure. Finally, the effect of ZrO2-nanoparticle doping in the package was investigated to enhance the uniformity of correlated color temperature (CCT) and luminous flux. This was attributed to the scattering effect of ZrO2 nanoparticles, which enhanced the utilization of blue light, and essentially eliminated the yellow ring phenomenon. Combined with its low cost, easy fabrication, and superior optical characteristics, ZrO2 nanoparticles can be an effective performance enhancer for the future generation of white light-emitting devices. In the second part, colloidal quantum dots (QDs) have attracted considerable scientific attention because of their unique properties such as high quantum yield, minimal backscattering, size dependent tunable bandgap, and narrow emission linewidth. Nowadays, major QD applications are currently focused on thin film display, monochromatic displays, and WLEDs. Therefore, extremely uniform colloidal QD-WLEDs with distributed Bragg reflector (DBR) that demonstrate a high color rendering index (CRI) and correlated color temperatures (CCTs) ranging from 2500 to 4500 K is proposed and experimental results indicate that the DBR capped onto the top of the package can increase the intensity of the QD emission by reflecting the UV light for both monochromatic QD-LEDs and QD-WLEDs. Then, pulsed spray coating method is employed to spray uniform RGB layers, and the polydimethylsiloxane (PDMS) film was used as the interface layer between each RGB color to avoid cross-contamination and self-assembly of QDs. Moreover, pixelated RGB arrays, 2-in. wafer-scale white light emission, and an integrated small footprint white light device were demonstrated. In addition, the hybrid white LED with polyfluoren (PFO) polymer and QD was investigated to obtain higher luminous efficiency at the different CCT for cool and warm color temperature. Consequently, the angular-dependent CCT and the thermal issue of the hybrid white LED device were also analyzed in this study. Finally, the output of this dissertation provided a great help on enhancing the light output and improving the uniformity of angular CCT for phosphor-based and QD-based LED and realizing the SSL and display application in next generation.
|Appears in Collections:||Thesis|