Plasma processing cuts solar cell production costs

Researchers at KAUST have used plasma processing in a chamber filled with CO2gas to deposit silicon oxide onto silicon wafers, an advance that could lower solar cell production costs. 

solar cell production costs
The team exposed silicon to carbon dioxide in plasma to allow for the controlled deposition of silicon oxide, and then overlaid another layer of silicon (© 2020 KAUST; Xavier Pita)

Semiconducting silicon is used in around 90 per cent of solar cell production, facilitating the generation of an electric current after it is doped with impurities.

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A technical challenge arises at the exposed surface of the silicon, described by Areej Alzahrani, a Ph.D. student at KAUST in Saudi Arabia, as the problem of so-called ‘dangling bonds.’

She said that the reduced availability of silicon atoms to bond together at the surface leaves scope for electrons ejected by light to recombine with the positively charged ‘holes’ that the departing electrons leave behind.

According to KAUST, this problem can be resolved by generating a layer of silicon oxide at the surface regions used to form electrical contacts. Several methods can achieve this, but they all come with difficulties and limitations. They also introduce an additional and costly fabrication step.

“The problems with existing methods challenged us to find a more simple and practical process,” Alzahrani said in a statement.

The solution involves exposing the silicon to carbon dioxide in plasma which allows controlled deposition of silicon oxide, followed by the overlaying of another silicon layer. Achieving these steps in the same chamber is claimed to offer a significant reduction in production costs. “This straightforward and simple process could be of great use to the solar cell industry,” Alzahrani said.

She said the team was surprised by the control that the method achieves over the deposition of an ultrathin silicon oxide layer with the required microstructure. It also generates oxide films that are more stable at high temperatures and tests revealed the procedure permits high voltages and low electrical resistance.

The team will now develop the processes commercial potential. “A first step will be to integrate this process into a complete and working solar cell, while also exploring improved light-capturing designs,” said research group leader, Stefaan De Wolf.

The team’s findings are published in Advanced Materials Interfaces.