The properties of n-μc-SiO:H inter-layers for thin-film silicon tandem solar cells

The n-type hydrogenated microcrystalline silicon-incorporated silicon oxide (n-μc-SiO:H) films are prepared by 13.56 MHz plasma enhanced chemical vapor deposition (rf-PECVD) using SiH
₄
, H
₂
and CO
₂
gases for an inter-layer between the amorphous silicon (a-Si:H) top-cell and the microcrystalline silicon (μc-Si:H) bottom-cell in the thin-film silicon tandem solar cells. The optical and electrical properties of n-μc-SiO:H prepared by varying deposition conditions are investigated. The refractive indices of the films are 2.1˜2.7 at the wavelength of 600 nm and the electrical conductivity is ˜ 5 × 10
^-3
S/cm. Compared to ZnO:Al inter-layer, the n-μc-SiO:H provides reduced current loss of μc-Si:H bottom-cells as well as enhanced current gain of a-Si:H top-cell which might be due to the reduced absorption of incident light in the n-μc-SiO:H inter-layer. An analysis on tunnel recombination junction using current-voltage measurements shows the non-ohmic behavior when crystalline volume fraction and conductivity of inter-layer are low, resulting in the reduction of the FF and V
_oc
in solar cells. The initial conversion efficiency of 10.66% is achieved in thin film silicon tandem solar cells with n-μc-SiO:H inter-layer.