| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 99 === Grow of thin-film polycrystalline Si (pc-Si) as a seed layer has been shown to be useful for further epitaxially thickening absorber layers for thin film solar cell. In order to effectively reduce the cost of seed layer, we propose in this thesis to deposit pc-Si via AIC process on a cheaper foreign substrate such as ceramics or glass which has better mechanical strength. The solar cell fabricated with this proposed process can be potentially used as bricks in the wall of building in the future.
Efficiency of pc-Si thin film solar cell is strongly dependent of grain size and amount of intragraunalr defect. The grain boundary and intragraunlar defects offer electron-hole recombination sites which lead to degrade the efficiency of thin film pc-Si based solar cell. Thus, defect-free large-grain pc-Si film appears to favor solar cell efficiency.
The poly-Si can be grown on a heterogeneous substrate from amorphous Si via aluminum induced crystallization (AIC) method with intermediary metals such as aluminum (Al) at low temperature. For increasing the reaction rate of AIC, in this work, we dope 1% Si into Al layer during AIC process. The effect of aluminum oxide thickness on AIC process, defect density in thin film, crystallinity and nucleation sites of Si grains in the Al layer are carefully studied using high resolution TEM/ EDX. We further discuss the mechanism of Si dopant in initial aluminum layer.
Si dopant in Al layer act as nucleation source in the AIC process, which offers rich nucleation sites to accelerate the reaction rate and reduce the annealing temperature. However, enhanced nucleation process suppresses the grain growth resulting in reduction of grain size. Furthermore, the twin density in poly-Si grains in the grown film with 1%Si doped process is higher than that via a undoped process. Furthermore, preferred orientation of Si grains is not {100} as in the case of undoped process.
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