Published on February 19th, 2017 | by Tina Casey0
Et Tu, Arizona? Red State Solar Cell Researchers Team Up With Blue State
February 19th, 2017 by Tina Casey
The old saying goes that all politics is local, but solar energy researchers at Arizona State University are upending the conservative political profile of their home with a new solar cell that uses low cost materials but performs almost as well as conventional silicon solar cells.
The discovery comes at a significant time, now that the deeply conservative former Oklahoma Attorney General Scott Pruitt is helming the US Environmental Protection Agency. Pruitt entered office last week with a mandate from Republicans to kill EPA from the inside. As expected, almost overnight he has transformed the agency into a cheerleader for fossil fuels, but he’ll have a tough time convincing the marketplace to give up on renewable energy that’s cheaper than coal, oil, or natural gas.
How To Have Your Solar Cake And Eat It, Too
Aside from connecting with California’s Stanford University, the Arizona team includes MIT from the deep blue state of Massachusetts, and Oxford University.
The new solar cell provides the one-two punch of low cost and high efficiency by combining silicon with perovskites (perovskites are a class of low cost, synthetic crystalline materials that mimic the properties of perovskite found in nature).
According to the research team, the new solar cell comesthisclose to conventional silicon with an efficiency rate of 23.6%.
That’s just for starters. The team is confident that they can boost it up to 30% within the next two years.
The new cell is actually two solar cells in one:
…the top cell is composed of a perovskite compound, a cheap, easily manufacturable photovoltaic material designed to excel at absorbing visible light. The bottom cell is made of silicon and is specifically tuned to capture infrared light. The perovskite and silicon cells boast efficiency of 15 and 21 percent, respectively.
What About Those Perovskites?
For those of you new to the topic, perovskites have bedazzled researchers in recent years because they are cheap and abundant. They were first used in solar cells just a few years ago and since then the field has made exponential strides in ramping up efficiency.
The National Renewable Energy Laboratory has enthused over the “transformational” potential of perovskite technology, with the prospect of “rapid terawatt-scale solar deployment” in view.
In other words, if you think solar is cheap now, you ain’t seen nothing yet.
There is a catch, though. Perovskites don’t hold up well outside of the laboratory. Here’s a rundown from ASU:
…perovskites have been limited by poor stability, degrading at a much faster rate than silicon in hot and humid environments. Additionally, perovskite solar cells have suffered from parasitic absorption, in which light is absorbed by layers in the cell that don’t generate electricity, which is problematic for tandems because that light needs to reach the silicon bottom cell for maximum efficiency.
ASU research partner Stanford was tasked with stabilizing the perovskite part of the new cell. That was basically a matter of improving the materials coated onto perovskite to keep it from degrading.
Applying those materials without damaging the delicate perovskite layer was another challenge the team had to address.
Yet another challenge involved applying the finished perovskite solar cell to the silicon layer. This part of the project was taken up by ASU:
…Due to the silicon cell’s rough nature, the relatively thin perovskite cannot be effectively layered on top. Zhengshan Jason Yu, a doctoral student at ASU, developed a method to create a planar surface only on the front of the silicon solar cell, ideal for the perovskite to be applied to the silicon.
How Low Can Solar Go?
A low cost solar cell is a matter of striking the right balance between the cost of the materials, the efficiency of those materials, and the potential for low cost, high volume production.
Perovskite offers a lot of promise on that score, but the ASU team better work fast if it wants to be the first to develop a commercial version of its perovskite-silicon solar cell.
Cambridge University researchers are also noodling around with a perovskite-silicon combo that could yield up to 50% efficiency, so they say.
Competition is also coming from other materials. A research team at Technion (the Israel Institute of Technology) is developing a different kind of combination solar cell that could climb into the 50-70% range.
Thin film solar cells are also in play. Though far less efficient, than silicon based solar cells, they are also generally less expensive and they can be applied to windows and other building elements.
Image (cropped): tandem perovskite solar cell via ASU.