A group of researchers from the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia said they discovered a process for depositing silicon oxide on silicon wafers to produce solar cells. The team employed a plasma processing method in a chamber filled with carbon dioxide gas to attain their goal.

Silicon is a semiconducting element and the material of choice for over 90% of solar cells available. However, when the silicon has been tampered with selected impurities, the sun’s energy creates electric flow.

According to Ph.D. student Areej Alzahrani, technical challenges arise at the exposed surface of the silicon, better known as the problem of ‘dangling bonds.’ Areej further explains that the reduced availability of silicon atoms to bond together at the surface provides room for electrons ejected by sunlight to recombine with the positively charged ‘holes’ that the departing electrons leave behind.

However, the chemical process called ‘passivation,’ where a layer of silicon oxide generated at the surface regions forms the electrical contact, thereby resolving the problem.

There are several methods to attain this, but it all comes with its limitations. The team also introduced an additional and costly fabrication step. “The problems with existing methods challenged us to find a more simple and practical process,” says Alzahrani.

The solution involves exposing the silicon to carbon dioxide in plasma – a low temperature ionized gas. The process allows the controlled deposition of silicon oxide, followed by the overlaying of another silicon layer, as required for building a solar cell. Accomplishing both these steps in the same chamber offers a significant reduction in production costs. “This straightforward and simple process could be of great use to the solar cell industry,” Alzahrani concludes.

The team was surprised by the control offered by the new technique over the deposition of an ultrathin silicon oxide layer with the required microstructure.

The process also generates oxide films that are more stable at high temperatures. Tests also revealed that the process also permits high voltages and low electrical resistance, perfect for efficient performance.

The team has plans to work on the commercial viability of the process. “The first step will be to integrate this process into a complete and working solar cell, while also exploring improved light-capturing designs,” said the research group leader, Stefaan De Wolf.

Meanwhile, HighLine Technology GmbH, a spin-off of Fraunhofer Institute for Solar Energy System ISE, claimed that it had developed a new dispensing technology, enhancing the electricity yield of silicon solar cells. The company also has plans to commercialize this technology.

Similarly, a research team from the South China University of Technology has claimed to have developed a new method of producing organic solar cells, which eliminate the need for potentially toxic materials while maintaining high conversion efficiencies.

 

Image credit: KAUST