Copper for silver cell swap expected to be commercialized "sooner" than expected

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Kaneka developed imec’s existing copper electroplating technology to achieve an efficiency of over 21 percent in six-inch silicon substrates – as measured by imec – kitted out with an electroplated copper contact grid on top of the transparent conductive oxide layer. The achievement is said to be a "world first", said the parties in a statement released.

Philip Pieters, business development director PV at imec additionally tells pv magazine that the work on copper metallization for silicon solar cells has been one of the "key activities" of the company’s Si-PV research and development program, established three years ago. He added that it was unsure as of yet whether the two parties would have the 21 percent efficiency independently verified.

Imec and Kaneka say that the electroplated copper is both an "economical" and "industry proven" process that eliminates the disadvantages of the traditional screen-printed silver which, they explain, include difficulties in lowering resistivity and thinning the metal lines. They add that higher efficiencies and lower production costs can be achieved via the new process.

When asked what the cost difference is between using silver and copper, Pieters stated, "We cannot comment on exact number at this at the moment, but the aim is to come to lower production cost and higher cell efficiencies. Further advantages are the facts that Cu has a lower resistivity and that electroplating allows obtaining higher aspect ratio’s for the lines and hence less shadow loss." Again, he could not comment when asked if the companies had manufactured any modules using the news cells.

In terms of when the technology can be expected to become commercially available, he explained, "To come to commercial products, long term reliability and cost effective production solutions need to be further proven. We believe this will be feasible because of the existing material knowledge experience and the existing electroplating experience in the R&D institutes like imec and in the industry. By leveraging on this experience, the use of Cu in commercial solar cell products may become sooner than some think."

The collaboration between imec and Kaneka was announced in September 2009 when Kaneka’s European photovoltaic laboratory was set up at imec’s Belgium premises.

23 percent efficiency

In other cell efficiency news, imec has announced that together with its silicon photovoltaic industrial affiliation program partners Schott Solar, Total, Photovoltech, GDF-SUEZ, Solland Solar, Kaneka and Dow Corning, it has achieved a conversion efficiency of 23.3 percent on an interdigitated back-contact (IBC) silicon solar cell. The area of the new cell is 2×2 cm2.

"Interdigitated back contacts are introduced to increase the conversion efficiency of crystalline silicon solar cells and allow for further reduction of the cell thickness, simplification of module fabrication and improved aesthetics of the final solar cell modules," explained the company in a statement released.

It added that key aspects of the new IBC silicon cells include: n-type base float-zone (FZ) silicon substrates; a random pyramid texture; a boron diffused emitter; phosphorous diffused front- and back surface fields; a thermally grown silicon dioxide for surface passivation; a SiN single layer anti-reflective coating; lithography based patterning; and aluminum metallization.