SiOx coating boosts PV cell efficiency during PSG etch

Equity Solar Inc. significantly increased cell efficiency using its room-temperature wet chemical growth (RTWCG) process for creating silicon oxide coatings on solar cells.

November 18, 2011 – Marketwire — Equity Solar Inc., which commercializes the solar photovoltaic (PV) technology of SPECMAT, significantly increased cell efficiency using its room-temperature wet chemical growth (RTWCG) process for creating silicon oxide coatings on solar cells.

The RTWCG process, used on the front side of a solar cell, boosts power conversion efficiency by 0.5% (absolute) on mono- and multi-crystalline silicon substrates. The target average efficiency for large area c-Si solar cells is 21%.

Chemical growth is performed in an existing phosphosilicate glass (PSG) etch tool. Easy adoption into existing cell fabs is a primary goal for Equity Solar.

With RTWCG, a 60-second chemical bath immersion grows a graded index of refraction SiOXantireflective coating (ARC), with a 5% to 9% AM1.5 weighted average reflectance; creates a selective emitter (SE) concomitantly with the ARC by etching back the emitter surface; passivates the surface; and cleans the surface and contacts.

Additional lithography steps are eliminated. The company estimates fabrication cost of a silicon solar cell to be 25-40% lower than that of conventional high-efficiency photovoltaics cells.

The silicon oxide growth chemistry created a thin oxide layer that improved surface condition and lowered reflectance, said Greg Knight, CTO of Equity Solar, adding that process optimization will likely improve performance further.

Now that the company has validated the process on a production line, it will choose a commercialization partner/s, said Equity Solar chairman Chester Aldridge.

The same underlying technology is in development at Equity Solar for back-side passivation during the existing emitter etch process. The chemistry grows silicon oxide on the rear side of the solar cell while removing the parasitic emitter. Initial data indicates increased cell efficiency, Knight reports.

Equity Solar, Inc. was specifically formed to commercialize a leading-edge patented solar photovoltaic (PV) technology licensed from Special Materials Research and Technology (SPECMAT). Details on the technology are available at http://www.specmat.com/solar%20cell%20specmat.html or visit www.equitysolar.com.

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