Fabrication Of Si-based Thin Films And Solar Cells

At present, in the industrial production, Si solar cells are undergoing the change from GenerationⅠ(crystalline Si) solar cells to GenerationⅡ(thin film) solar cells. In the laboratory, researchers have started to investigate GenerationⅢ(large efficiency) solar cell, the tandom solar cell becomes the focus due to its simple process of preparation. Microcrystalline Silicon Germanium thin film is widely applied in the tandom solar cell as middle or bottom material because of better optical stability, larger mobility, narrower and varied band gap.In this thesis,μc-Si:H andμc-SiGe:H films were prepared by PECVD at low temperature (250℃) using H2 and Ar as diluted gases. The growth mechanism, microstructure and optoelectronic properties of microcrystalline silicon germanium thin films are analysised. Meanwhile, a-Si solar cells were fabricated using Si3H8 as the source gas, the performance of the solar cell was characteristed and analysised. The outline of the thesis is shown as follows:Theμc-Si:H films were prepared by PECVD at low temperature, the results reveal that the addition of Ar in the diluted gases can efficiently improve the deposition rate and crystallinity. H2 and Ar all play a positive role in the formation ofμc-Si:H films: H2 promotes the mobility of the precursor and saturates the dangling bonds; Ar not only increases the dissociation efficiency of source gas, but also annealing the growth surface by bombardment of Ar* to surface, in which released energy results in the increase in crystallinity.Theμc-SiGe:H films were prepared and the influence of H2 and Ar flow rate on the structure and optoelectronic properties was investigated. The film crystallinity ofμc-SiGe:H films increased with the increasing Ar flow rate. Film density and optoelectronic properties improved with increased H2 flow rate.The a-Si solar cell was fabricated by PECVD using Si3H8, a new gas, as source gas. The efficiency of a-Si solar cell with Si3H8 as a source gas was larger than that with SiH4 as source gas. We believed that the film prepared by Si3H8 had larger compactness, minor density of localized states. Si3H8 is a promising gas for preparation of Si-based solar cell.