Study of the effects of different fractions of large grains of μc-Si:H:F films on the infrared absorption on thin film solar cells

We have studied microcrystalline silicon films (μc-Si:H:F) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) at low temperature (∼200 °C) from SiF4, H2 and Ar gas mixtures. We found that the H2/SiF4 ratio plays an important role on the crystalline fraction of the films, specifically on the films grain size, deduced from UV–vis spectroscopic ellipsometry. We observed that higher crystallinity (and larger fraction of large-grains) in the films provides a higher absorption on the infrared (IR) region, which is of particular interest for tandem solar cells. PIN solar cells were fabricated with intrinsic μc-Si:H:F films of different crystallinity (and different fraction of large grains) in order to observe their effect on the solar cells IR absorption and on the cells performance characteristics.

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► We report the study of μc-Si:H:F films deposited by Plasma Enhanced Chemical Vapor Deposition.
► Films were deposited at low temperature (∼200°C) from SiF4, H2 and Ar mixtures.
► We found that the H2/SiF4 ratio plays an important role on the crystalline fraction of the films.
► High large grain fraction (LG) on the μc-Si:H:F films results in larger absorption of IR radiation.
► A high LG fraction on μc-Si:H:F in PIN solar cells results on a large external quantum efficiency.