Preparation of amorphous hydrogenated silicon-germanium material and solar cells using the thermocatalytic chemical vapor deposition

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Abstract
Hydrogenated amorphous silicon-germanium (a-SiGe:H) films were produced by the “thermocatalytic chemical vapor deposition” [(TC-CVD) also called “hot-wire” CVD] method. With respect to proposed superstrate solar cell application of the material, the substrate temperature was kept around 200 °C. The band gap Eg of the films could be varied between 1.1 and 1.77 eV by changing the ratio of silane to germane flow. The photoelectronical properties of the alloy films have been found sufficient for solar cell application when Eg⩾1.5 eV and deteriorate for further reduction of the band gap. Using the concept of band gap grading, p-i-n solar cells containing a TC-CVD-a-SiGe:H i layer with initial conversion efficiencies up to η=6.42% (Eg=1.5 eV) have been fabricated. The influence of moderate hydrogen dilution of the process gas on the conversion efficiency and stability of the solar cells has also been investigated.