利用漸變式矽過多氧化矽多層膜結構製做高密度矽量子點薄膜於光伏元件之應用

Abstract

矽基太陽能電池是目前全球市佔率最高的太陽能電池種類，加上其原料充足與製程技術成熟等優勢，未來前景仍相當被看好；為了更進一步提升元件效率與降低製程成本以達到第三代太陽能電池的目標，全矽基多接面太陽能電池正被廣泛地研究與開發。而其中具奈米結晶態的矽量子點薄膜則被視為極具潛力能克服矽基材料的能隙限制，以解決短波長光子的嚴重損耗議題。 截至目前，國際上的研究團隊製做的矽量子點薄膜以矽過多氧化矽(silicon-rich oxide)單層膜或二氧化矽(silicon dioxide)/矽過多氧化矽(silicon-rich oxide)多層膜結構為主，但前者不易調控量子點尺寸，後者則有量子點間距過大的問題，加上兩者皆無法達到高密度的矽量子點形成，導致元件的光激載子傳輸嚴重受限，整體效率仍有待改善。 故本篇論文提出以漸變式矽氧濃度之氧化矽薄膜取代二氧化矽侷限層的構想，藉由在沉積時連續性調控矽氧組成比，使其每一週期的矽濃度呈現漸變式分佈(低□高□低)，以此漸變濃度結構輔助後續退火過程中的奈米結晶矽形成，期望能同時達到矽量子點的尺寸調控及間距縮短，大幅改善光激載子傳輸效益，以提升矽量子點型太陽能電池之工作效率。

So far, the Si-based solar cell is the highest global market share and the good development potential due to the plentiful materials and the well-developed fabrication technique. In order to achieve the goal of the third generation solar cells with high efficiency and low cost, all Si-based multiple-junction solar cell is widely investigated and developed nowadays. The nano-crystalline Si quantum dot (QD) thin film is one of the potential structures to overcome the bandgap limitation of Si-based materials. Silicon-rich oxide (SRO) single layer and [SRO/SiO2] multilayer (ML) thin films are the most commonly used deposition structures for Si QD thin films. However, the former is hard to control the QD's size and density simultaneously, the latter exists the QD’s separation limitation due to the SiO2 barrier layers inserted. Furthermore, the QD’s density of both structures is still not high enough for a better PV application. These result in the difficulty for good photo-generated carrier’s transportation and high conversion efficiency. Hence, to efficiently improve the carrier’s transportation properties is a critical issue for the high efficiency Si-based solar cells integrating Si QD thin film. In this study, we propose a more potential deposition structure by a gradient Si-rich oxide multilayer (GSRO-ML) structure for the QD size control and the high QD density. The nano-structure, crystalline, and optical properties of Si QD thin films using a GSRO-ML structure had been studied. It also shows the better photovoltaic properties than that using a [SRO/SiO2]-ML structure. A higher conversion efficiency of Si QD thin films utilizing a GSRO-ML structure can be highly expected by using a heavy doping concentration in the near future.