| Summary: | 博士 === 國立交通大學 === 光電工程研究所 === 104 === Low dimensional materials have attracted considerable scientific attention because of the unique material properties when the size of materials is in the scale of nanometer. The low dimensional materials includes zero-dimensional materials, such as quantum dots (QDs), one-dimensional materials, such as nanowire, or two-dimensional materials, like graphene or transition metal dichalcogenides (TMDCs). In recent years, the QDs rapidly developed because of exhibiting superior physics and chemicals properties and there are many applications of QDs in optoelectronic devices, such as light-emitting diodes, backlight modules, photo-detectors, and bio-photonics. On the other hand, recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics. In this dissertation, we use the luminescent down-shifting effect of QDs to design a novel and highly efficient hybrid QDs solar cells and to combine with ultra-violet micro LED arrays to be a display application without color filters. Then, for the two-dimensional materials, we utilize simple hydrohalic acids treatment to be an effective strategy for promoting the excitonic emission of defective monolayer TMDCs.
In the first part of this study, we propose several methods to utilize the solar spectrum in order to increase the power efficiency of solar cell. Among the all mechanisms, down-shifting effect is investigated in detail. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. This hybrid design effectively boosts photon harvesting at long wavelengths while enhancing the collection of photogenerated carriers in the ultraviolet region. A multiple layer structure is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved. The optimization properties of concentration and the emission wavelength of colloidal quantum dots also be investigated.
Second, the conventional liquid crystal displays have much energy loss, which is due to the light absorption from backlight module and color filter. Colloidal quantum dots which can emit red, green, and blue colors are incorporated with a micro-LED array to demonstrate a feasible choice for future display technology. We utilize Aerosol Jet printing system to spray quantum dots onto the micro light-emitting diode array. The ultra-violet LEDs are used in the array to excite the red, green and blue quantum dots on the top surface. To increase the utilization of the UV photons, a layer of distributed Bragg reflector was laid down on the device to reflect most of the leaked UV photons back to the quantum dot layers. Moreover, the full-color micron display that is manufactured by quantum dots can improve the color gamut of the display. The color gamut NTSC reached the ultrahigh value about 152%.
In the third part, here we report an effective strategy for promoting the excitonic emission of defective monolayer TMDCs by simple hydrohalic acids treatment (HBr, HCl, and HI). The chemical treatment can effectively enhance the photoluminescence intensity of atomically thin MoSe2 for more than 30 times. We further invest the behaviours of exciton and trion PL in the treated TMDCs by temperature dependence measurement, and observe a significant suppression of trap state exciton, which lead to a promoted exciton and trion emission in defective TMDCs through the p-doping process. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring optical properties of monolayer TMDCs.
Finally, the output of this dissertation provided a great help on enhancing the light absorption and improving the power conversion efficiency of solar cells, demonstrating a high vivid, saturated full colors quantum dot micro display technologies, and working on the acids treatment for the TMDCs to reduces the n-doping in MoSe2 and the structural defects.
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