Solar Needs to be Sustainable Too! - Summer 2018 Newsletter

By Anthony Aguilar, ASU Solar Power Lab, PhD Candidate in the School of Electrical, Computer and Energy Engineering

A copper plated silicon heterojunction solar cell being held up in front of the ASU facility where it was created. ASU’s Solar Power Lab is the only public access facility in the United States that can completely produce a solar cell from a silicon wafer in-house.

 

Research into copper electroplating is fully under way at ASU due to the dramatic implications in terms of sustainability in the solar cell industry. Implementation of copper into a solar cell processing line would create a cheaper and more efficient solar cell that would not rely on any precious metals.

 

Colored Scanning Electron Microscope (SEM) image of electroplated copper finger showing excellent adhesion to silicon during a stress test. Adhesion tests are one of many tests performed to help industry determine physical quality of new types of metal electrodes (makes sure metal doesn’t scrape off during processing!).

Currently, the industry standard is to screen print a glass-silver paste to form the front electrode of the solar cell because it is a well-defined process that is capable of being performed in a matter of seconds. Companies are therefore reluctant to change their processing line to include new materials, such as copper. Unfortunately, silver is a precious metal that is used extensively by many industries. In most of these industries, the silver is used and thrown away in landfills because it is currently too difficult and expensive to extract or recycle. This quickly decreases the amount of usable silver on Earth. The solar industry uses ~8% of the world’s annual silver production and is expected to rise as solar becomes cheaper. A large field of research is being conducted on ways of electroplating copper to solar cells. Copper is much cheaper than silver and because electroplating deposits copper in a near pure form, a solar cell with a copper front grid would have a higher efficiency than its screen-printed glass-silver counterpart. Eventually, the decrease in silver quantity will lead to silver prices increasing, which would make conventional solar cells too expensive to produce. Only then will it be economically viable for industry to switch to copper electroplating.

 

The Solar Power Lab at ASU is researching several different means of electroplating to make copper front grids economically viable now. If we can procure a method to making it appealing to industry, we can avoid being part of a larger problem when the silver eventually runs out.