CZTS cells offer a cheap alternative to indium thin films

The hunt for inexpensive thin films for solar cells is a hot topic of current research.  

Today, solar power has many downsides -- polycrystalline silicon panels are fragile (non-bendable) and relative expensive -- plus they're limited in efficiency, without failure-prone concentrating technology.  But more durable, efficient thin film cells can be even more expensive.

Researchers at Oregon State University (OSU) have published a paper [abstract] in the peer-reviewed journal Physica Status Solidi A detailing a production method for Cu2ZnSnS4 (CZTS) cells.  CZTS cells are much cheaper than the indium based thin film cells that dominate current production.  But producing the CZTS nanoparticles necessary has been a time consuming (and hence expensive) process.

Traditionally heating is accomplished by radiating coils or other mechanisms, but researchers at OSU dreamt up an innovative solution -- using microwaves to rapidly react the ingredients.

The microwave raised the solution temperature to 190 deg. Celsius for 30 min.  The resulting cells efficiency was 0.25 percent.  Past work [abstract] has shown 7.2% efficient cells produce with conventional (225 deg. Celsius) heating, with a similar (30 min.) heating time.

But the OSU team suggests the microwave heating process is cheaper and could eventually be reduced to "seconds".  Comments the senior author, Associate Professor Greg Herman, "This approach should save money, work well and be easier to scale up at commercial levels, compared to traditional synthetic methods.  Microwave technology offers more precise control over heat and energy to achieve the desired reactions."

CZTS microwave
OSU has showed promising results with microwave produced cells.
[Image Source: Physica Status Solidi A]

The team says the previous (7.2% efficient) study got better results largely because the nanoparticles were produced in vacuum to eliminate impurities that occur when producing in a reactive atmosphere.

The team is bullish on CZTS cells, with Professor Herman commenting, "All of the elements used in this new compound are benign and inexpensive, and should have good solar cell performance.  Several companies are already moving in this direction as prices continue to rise for some alternative compounds that contain more expensive elements like indium.  With some improvements in its solar efficiency this new compound should become very commercially attractive."

The work was funded by Sharp Laboratories of America (a Sharp Corp. (TYO:6753) property), the Oregon Nanoscience and Microtechnologies Institute, and the Oregon Process Innovation Center for Sustainable Solar Cell Manufacturing, an Oregon BEST (Built Environment & Sustainable Technologies) signature research facility.  Oregon BEST is a nonprofit research effort authorized by Oregon's legislature.

Sources: Physica Status Solidi A [abstract], Oregon State [press release]

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