24-01-2012, 02:09 PM
Crystalline-Silicon Solar Cells for the 21st Century
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ABSTRACT
The worldwide market share for crystalline-silicon solar cells has
increased steadily in the last 10 years. In 1998, about 87% of the
photovoltaic modules shipped worldwide are based on crystalline
silicon. This dominance will likely continue into at least the first few
years of the 21st century. The long-term growth of crystalline-silicon
solar cells will depend on the development of low-cost polysilicon
feedstock, silicon films, and advanced cell and module manufacturing
processes.
INTRODUCTION
The worldwide photovoltaic (PV) module shipments for terrestrial applications
reached 152 MW/year in 1998. Crystalline-silicon (c-Si) solar cells currently account
for about 87% of the worldwide PV module shipment
LOW-COST POLYSILICON FEEDSTOCK
For crystal-growth feedstock, the c-Si PV industry has been relying on waste
material from the semiconductor Si industry and on secondary polysilicon, the excess
or rejected material from electronic-grade polysilicon production. This amounts to
about 10% of the polysilicon material used by the semiconductor Si industry.
Porous Silicon
It was discovered in 1990 that porous silicon formed on crystalline-silicon wafers
using electrochemical etching exhibits photoluminescent and electroluminescent
properties similar to those properties of a semiconductor with a direct energy gap
(22). Porous silicon layers can be easily produced on single- or multicrystalline
silicon surfaces by electrochemical or stain etching at very low cost.
CONCLUSIONS AND DISCUSSION
With increasing automation and economy of scale, the present generation of
crystalline-silicon solar cells, including single-crystal wafers, polycrystalline wafers,
ribbons, and sheets will continue to dominate the photovoltaic solar cell market for at
least the first ten years of the 2lst century. The substrate areal throughputs for the
leading growth processes are in the range 5-20 m2/h per growth station, and matching
process line rates are in place
