New Jersey-based Natcore Technology Inc. and Rice University in Houston, have demonstrated a copper-based catalyst as an alternative to silver for use in etching photovoltaic energy cells.
According to Andrew Barron, Rice professor and a Natcore co-founder, even though a very small amount of the catalyst is used to make a single solar cell, Natcore says the potential savings are significant in large-scale projects.
The process uses a mix of copper nitrate, phosphorous acid, hydrogen fluoride and water. When applied to a silicon wafer, the phosphorous acid reduces the copper ions to copper nanoparticles. The nanoparticles aid in removing electrons from the silicon wafer's surface, thereby oxidizing it. The oxidized silicon is dissolved by the hydrogen fluoride, resulting in a process that forges inverted pyramid-shaped structures into the silicon.
The result of fine-tuning the process is a black silicon layer with features as small as 590 nanometers that reflect less than 1% of light. By comparison, a clean, un-etched silicon wafer reflects nearly 40% of light.
Natcore has produced solar wafers using its ‘black silicon’ process and has engaged the Fraunhofer Institute for Solar Energy Systems to test them.
‘There are still some challenges to overcome,’ Barron says. ‘The spikes would still require a coating to protect them from the elements, and we're working on ways to shorten the process needed to perform the etching in the lab. We also need to completely remove the copper catalyst in order to extend the life of the solar cell.’
The research by Barron and Rice graduate student and lead author Yen-Tien Lu appears in the Royal Society of Chemistry's Journal of Materials Chemistry A.