Si and Ge Solar Cell Efficiency Records Set
Peter Singer, Editor-in-Chief -- PV Society, 10/11/2007
It was announced at SEMICON Europa this week that new records for thin-wafer silicon and germanium solar cells were set by IMEC (Leuven, Belgium). The research consortium realized an impressive efficiency of 17.4% for its thin-wafer silicon solar cells realized with its industrial passivated emitter and rear cells (i-PERC) process. By using the i-PERC process as a method to passivate the rear side and create local contact, efficiencies above 20% are definitely within reach, IMEC reported.
To reduce the cost of solar cells, it is imperative to lower the amount of ultrapure silicon. The most straightforward way to achieve this is the use of very thin silicon wafers. The i-PERC process uses very thin silicon layers (&180 µm) in which the classical aluminum back-surface field, covering the whole rear of the silicon solar cell, is replaced by local aluminum-alloyed contacts. In this process, the rear is passivated by a dielectric stack, in which the contact openings are formed by laser ablation. Subsequently an aluminum contact layer is evaporated and then fired in a belt-line furnace to create local back-surface fields. Further process optimization yielded an efficiency of 17.4% on thin large-area multi-crystalline silicon substrates. Screen printing was used to form the contacts.
| Large-area i-PERC solar cell on a very thin wafer. |
To get more evidence of the efficiency potential of the i-PERC process, IMEC also developed small-area crystalline silicon solar cells with evaporated contacts. Lab-scale silicon solar cells have been realized where, for the first time, the i-PERC process has been used as a method to passivate the rear side and create local contacts. At the front side, random pyramids are used in combination with a standard silicon nitride layer to provide good optical properties and surface passivation. The evaporated Ti/Pd/Ag front-contact grid is patterned by standard lithography. First attempts immediately resulted in an efficiency of 19%, with an impressive short-circuit current of more than 39 mA/cm2. The results indicate that with the i-PERC approach, efficiencies above 20% are definitely within reach.
Progress was also reported in the field of germanium cells for thermophotovoltaic applications or as a bottom cell in photovoltaic stacks. Compared with its previous record of around 8% (which is high for a low-bandgap material like germanium), IMEC jumped over the 8.5% barrier, coming close to the theoretical limits for germanium. The cells proved to be stable under thermal cycling, and kept a good performance up to concentration levels of ~15 suns.
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So, does it mean that Solar Cell MObile Phone is expected near future? If that so, then, thinner and environmental-protection Mobile Phone will coming down to the World. I personally believe anyone who develops 1st this kind of Mobile Phone will be the winner. Is this dream coming true? Lithon Battery exists some disadvantages, including jeoparize people at some extent under some circumstances, plus it dangers the earth environment
Debbie - 01-13-2008 10:53:00 CST -
Good article.Would it be possible to send me a general process flow of the solar cell manufacturing.
Thank you.
Ismail Kashkoush
Ismail - 11-19-2007 11:31:00 CST
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