The 1-volt barrier has been tantalizing solar researchers for a long time, and a team headed up by the National Renewable Energy Laboratory has just figured out how to break through it. Okay, so one volt doesn’t sound like such a lofty goal, but it is when the topic at hand is CdTe, short for cadmium telluride. CdTe solar cells are starting to make waves in the solar market and the new breakthrough could “pave the way for solar energy to directly compete with electricity generated by conventional energy sources,” according to the folks at NREL.
CleanTechnica has been following the CdTe company First Solar, so we’ll take this opportunity to catch up with them as well.
What’s Holding CdTe Solar Back
The US Energy Department has been eyeballing CdTe solar cell technology for a long time. CdTe currently represents less than 10 percent of the global solar market and silicon gobbles up practically all the rest, but the percentages could flip because of CdTe’s high efficiency potential and low cost manufacturing process compared to silicon solar cells.
Aside from being low cost, according to the folks at NREL CdTe manufacturing has a lower carbon footprint, and CdTe solar cells have the potential to perform better than silicon in hot weather, humidity, and less than optimal sunlight.
The key word is potential. The company First Solar has been unlocking the secrets of CdTe (more on that in a minute), but as NREL sees, it, CdTe solar cells could be pumped up to the point where they can compete with high efficiency mulitcrystalline silicon solar cells. Here’s the rundown on CdTe solar cells from NREL:
One key area where CdTe has underperformed is in the maximum voltage available from the solar cell, a measure called open-circuit voltage. The quality of CdTe materials has prevented industry, universities, and national laboratories for the past 60 years from obtaining open-circuit voltage exceeding 900 millivolts on billions of solar cells; the vast majority have been limited to 750 to 850 millivolts.
CdTe Solar Cell Breakthrough: #thanksobama
If you caught that thing about materials quality, that’s one key to the breakthrough. NREL collaborated with the University of Tennessee and Washington State University for the CdTe project, which aimed at creating a more pure form of CdTe than possible under conventional processing step.
Conventional CdTe processing pivots on cadmium chloride. The alternative developed by NREL and its collaborators involves a new process:
…they placed a small number of phosphorus atoms on tellurium lattice sites and then carefully formed ideal interfaces between materials with different atomic spacing to complete the solar cell. This approach improved both the CdTe conductivity and carrier lifetime by orders of magnitude, enabling fabrication of CdTe solar cells with an open-circuit voltage breaking the 1-volt barrier for the first time.
Washington State further explains that the new CdTe process deploys a method called “melt growth.” Materials are mixed and prepared in a specialized clean room, and placed in a furnace above 1100 degrees centigrade. Under controlled cooling from the bottom up (the rate is about one millimeter per hour), the material forms a crystal, which can then be cut into wafers for solar cells.
For all the details on the CdTe solar breakthrough check out the study in the journal Nature Energy under the title “CdTe solar cells with open-circuit voltage breaking the 1 V barrier.”
The authors note that CdTe technology has languished under the 1 volt mark “for decades” and has been outperformed by other materials with less solar-friendly characteristics, namely gallium arsenide (GaAs).
The collaboration was funded through the Energy Department’s SunShot initiative, which launched in 2011 and has received lots of TLC from the Obama Administration in the form of funding and public-private partnerships, so group hug for all us taxpayers and #thanksobama.
First Solar Not Waiting Around For CdTe
Meanwhile, First Solar has been not been sitting on its hands. Back in 2011 CleanTechnica noted that the company set a new world efficiency record for its CdTe solar cell technology at 17.3 percent, a significant achievement considering that the previous record of 16.7 percent had been set in 2001.
That’s nothing to sneeze it, but go ahead and sneeze anyway. Just last month, First Solar reported a new record of 22.1 percent.
First Solar has also been hammering away at lowering manufacturing costs for its CdTe solar modules.
On a side note, our sister site Planetsave has noted First Solar’s forays into the community solar field through a partnership with the Clean Energy Collective. The idea is to provide an alternative to rooftop solar, so for example, if you don’t want to give up your tree-lined backyard, you can still buy into clean power.
While rooftop solar and other on site forms of clean power have their pluses, it’s also important to recognize other solar options that enable land use flexibility, an issue we discussed earlier this week in an article on Masdar City.
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