Preparation of Microcrystalline Silicon Based Solar Cells at High i-layer Deposition Rates Using a Gas Jet Technique
- PDF / 453,067 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 90 Downloads / 239 Views
Preparation of Microcrystalline Silicon Based Solar Cells at High i-layer Deposition Rates Using a Gas Jet Technique S.J. Jones*, R. Crucet*, X. Deng*, D.L. Williamson** and M. Izu* *Energy Conversion Devices, Inc., Troy, MI 48084 ** Colorado School of Mines, Golden, CO 80401 ABSTRACT A Gas Jet technique has been used to prepare microcrystalline silicon (µc-Si) thin films at deposition rates as high as 20 Å/s. The films have microcrystal sizes between 80 and 120 Å 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 Å/s). Using a 610nm cutoff filter which only allows red light to strike the device, pre-light soaked short circuit currents of 8-10 mA/cm2 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. INTRODUCTION µc-Si-based solar cells are an intriguing alternative to other cost effective, thin film photovoltaic devices. Absorbing a significant portion of the solar spectrum, reasonably high stable efficiencies can be obtained with single-junction device structures. For example, Shah et. al.[1] have shown that high quality µc-Si pin devices with 8.5% efficiencies that absorb a significant amount of the red light and do not degrade with long term light exposure can be made using the Very High Frequency (VHF) PECVD technique. As another alternative, the µc-Si material could replace amorphous silicon germanium alloy (a-SiGe:H) layers as the red-light absorbing structures in amorphous silicon-based multi-junction structures. The a-SiGe:H alloys have historically been more defective and of poorer quality than the a-Si:H materials and in many respects limit the efficiencies of the multi-junction devices. The µc-Si cells do not significantly degrade (10%). Also use of the µc-Si cells as red-light absorbing structures in multi-junction cell with blue-green light absorbing a-Si:H top cells would lead to the elimination of costly germane gas from the fabrication process. The present major disadvantage in using the µc-Si dev
Data Loading...
