Preparation of microcrystalline silicon based solar cells at high i-layer deposition rates using a gas jet technique

摘要

A Gas Jet technique has been used to prepare microcrystalline silicon (μc-Si) thin films at deposition rates as high as 20 A/s. The films have microcrystal sizes between 80 and 120 A with a heterogeneous microstructure containing regions with columnar growth and other regions with a more randomly oriented microstructure. These materials have been used as i-layers for nip single-junction solar cells. The high deposition rates allow for fabrication of the required thicker μc-Si i-layers in a similar amount of time to those used for high quality a-SiGe:H i-layers (rates of 1-3 A/s). Using a 610 nm cutoff filter which only allows red light to strike the device, pre-light soaked short circuit currents of 8-10 mA/cm{sup}2 and 2.7% red-light efficiencies have been obtained while AM1.5 white light efficiencies are above 7%. These efficiencies are higher than those typically obtained for μc-Si cells prepared at the high i-layer growth rates using other deposition techniques. After 1000 h of light soaking, the efficiencies on average degrade only by 2-5% (stabilized efficiencies of 2.6%) consistent with the expected high stability with the microcrystalline materials. The small amount of degradation compares with the 15-17% degradation in efficiencies for a-SiGe:H cells subjected to similar irradiation treatments (final light-soaked red light efficiencies of 3.2%). Improvements in the cell efficiencies may come through an understanding of the role that columnar microstructure and void structure plays in determining the device performance.