APSTL Claims Crystalline Silicon Advance
Advanced Packaging & Systems Technology Laboratories LLC (APSTL, Scottsdale, Ariz.) says it is making progress on development of a thin crystalline silicon on substrate (TCSS) technology for production of photovoltaic (PV) cells at much lower costs than thick crystalline silicon wafers. The approach involves creation of a 50 micron layer of polycrystalline p+ silicon deposited on an aluminum substrate.
David Lammers, News Editor -- Semiconductor International, 9/24/2008 10:00:00 AM
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| A cross section of 50 µm layer of polycrystalline p+ silicon deposited on an aluminum substrate. (Source: APSTL) |
The company is not publicly disclosing much about how it achieves what it claims, Gupta said, other than saying the approach is driven by an understanding of imperfections in silicon and their effect on electron transport, as well as “the effect of deposition processes and crystal growth conditions on the creation of various defects.”
While unable to disclose its proprietary intellectual property, the technology development company laid out the rationale for the TCSS technology, saying that it will “extend reliable crystalline silicon technology into the <$2/Wp segment of PV modules, and at the same time provide it with panels 50% more space-efficient and more rugged compared to glass substrate-based thin-film technologies.”
Also, the TCSS approach could reduce the need for thick silicon wafers and the expensive polysilicon production infrastructure. Silicon wafers have a crystalline atomic structure which enables a conversion efficiency of ~15-22 %, nearly double that of current thin-film PV panels. However, the relatively thick crystalline silicon wafers, Gupta said, are made with an “archaic process.” The wafers need to be relatively thick for handling purposes, even though the crystalline silicon layer needs to be only ~80 µm thick for the maximum absorption of photons and conversion to electrons.
TCSS wafers may enable the silicon wafer-based PV manufacturing infrastructure to become more cost-competitive with the latest thin-film technologies, he said. The thin-film PV approaches require relatively costly deposition tools to deposit amorphous silicon, or the compound Cd-Te, CdS, CIS and CIGS films.
Besides the tooling costs, thin-film PV development “has been relatively slow for the more complex thin-film formulations, including compound semiconductors such as CIS and CIGS,” Gupta said. The thin-film vendors face “yet unresolved fundamental materials issues such as the impact of processing on non-uniformity, phase separation, and defects in the deposited films, with consequences on conversion efficiency,” he said.
