Effect of reducing impurity concentration of microcrystalline silicon thin films for solar cells using radio frequency hollow electrode enhanced glow plasma

Microcrystalline silicon (μc-Si) thin films with low impurity (oxygen) concentrations were prepared by radio frequency hollow electrode enhanced glow plasma (RF-HEEPT). By using metal gasket seals with the RF-HEEPT system, the oxygen concentration in the thin films was reduced to 3.0 × 1017 cm−3, which is approximately two orders of magnitude less than that of films fabricated in a system using rubber gasket seals. Under the reduced oxygen conditions, we were able to deposit μc-Si thin films at a maximum deposition rate of 10.0 nm/s. We also investigated the spectral response of μc-Si thin-film solar cells. The spectral response of the solar cells fabricated with a low oxygen concentration was improved, especially in the near-infrared region. However, with increasing deposition rate of the thin films, the peaks of the spectral response shifted toward shorter wavelengths and the magnitudes decreased, especially in the near-infrared region, indicating that grain boundaries or defects in the thin films increased at higher deposition rate.