Laser Processed Materials for Advanced Solar Devices
Crystallized hydrogenated amorphous silicon (a-Si:H) by various methods have been studied for a long time, and among these techniques, excimer laser crystallization has the merits in rapid and stable. In this PhD project, the objective of the excimer laser processing is to develop 1) crystallized a-Si:H thin film as a promising field & thermionic emission candidate, and 2) a novel dark film – black silicon, which can highly absorb lights. And finally, a thermionic emission enhanced renewable energy device is purposed, which also adopt black silicon as the sunlights absorber. This PhD thesis starts from the investigation of excimer laser processing hydrogenated amorphous silicon which resulting in the formation of the microstructures and change of the thermal, optical and electrical properties. The goal of this research is to perform an intensively study to understand this silicon based materials by experiments. Various thickness of the a-Si:H which leads to different applications such as ‘black silicon’ layer, obtained by excimer laser to process thick (~400 nm) a-Si:H layer while a thinner (100nm) laser irradiated a-Si is a novel field emitter. This film has a black surface by the direct observation. A well understanding is then established via studying the microstructure by SEM images and optical experiments. With the principle of the fabrication of black silicon, a n-i-p junction silicon nanowire solar device was fabricated and studied by the means of excimer laser process and doping. The device is able to enhance the light trapping due to the micro structure to strengthen the solar cell efficiency compared to the conventional planar amorphous silicon solar device. The field and thermionic emission of excimer laser irradiated thin amorphous silicon (emitter) was then investigated to develop a prototype of photon enhanced solar thermal device with the black silicon layer as the light absorber. In this device, the lights are trapped by the bSi and the heats are transformed to the emitting cathode via the copper foil between the bSi and cathode. The thermal collected from bSi and passed to the emitters then enhances the threshold field of the emitters and electrons are launched via cathode and travel to the anode to form a electricity loop.
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