Effect of hydrogen on surface texturing and crystallization of a-Si:H thin film irradiated by excimer laser |
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Authors: | Hongliang Wang Fernando Lusquiños Y Lawrence Yao |
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Institution: | (1) Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA;(2) Department of Applied Physics, University of Vigo, Vigo, 36310, Spain |
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Abstract: | Hydrogenated amorphous silicon (a-Si:H) thin films have been considered for use in solar cell applications because of their
significantly reduced cost compared to crystalline bulk silicon. However, their overall efficiency and stability are lower
than that of their bulk crystalline counterpart. Limited work has been performed on simultaneously solving the efficiency
and stability issues of a-Si:H. Previous work has shown that surface texturing and crystallization on a-Si:H thin film can
be achieved through a single-step laser processing, which can potentially alleviate the disadvantages of a-Si:H in solar cell
applications. In this study, hydrogenated and dehydrogenated amorphous silicon thin films deposited on glass substrates were
irradiated by KrF excimer laser pulses and the effect of hydrogen on surface morphologies and microstructures is discussed.
Sharp spikes are focused only on hydrogenated films, and the large-grained and fine-grained regions caused by two crystallization
processes are also induced by presence of hydrogen. Enhanced light absorptance is observed due to light trapping based on
surface geometry changes of a-Si:H films, while the formation of a mixture of nanocrystalline silicon and original amorphous
silicon after crystallization suggests that the overall material stability can potentially improve. The relationship between
crystallinity, fluence and number of pulses is also investigated. Furthermore, a step-by-step crystallization process is introduced
to prevent the hydrogen from diffusing out in order to reduce the defect density, and the relationship between residue hydrogen
concentration, fluence and step width is discussed. Finally, the combined effects show that the single-step process of surface
texturing and step-by-step crystallization induced by excimer laser processing are promising for a-Si:H thin-film solar cell
applications. |
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