Solar cells that are cheaper to produce and contain fewer toxic compounds may be a reality in the near future, thanks to new research from Oregon State University.
By utilizing a commonly used antifreeze — ethylene glycol — and some other comparatively cheap materials to produce solar cells in a “continuous flow reactor,” the costs of solar cell manufacturing can be cut down considerably, according to the researchers. A continuous flow reactor is an approach to creating thin-film solar cells that could be easily scaled up to industrial levels.
The research has found that ethylene glycol can function effectively in a continuous flow reactor as a low-cost solvent, replacing more expensive options. The researchers also discovered that the approach will work with CZTS — copper zinc tin sulfide — a compound that had already gotten the attention of researchers in the solar energy field thanks to its notable optical properties and the reality that the compound is cheap and relatively environmentally benign.
“The global use of solar energy may be held back if the materials we use to produce solar cells are too expensive or require the use of toxic chemicals in production,” stated Greg Herman, an associate professor in the OSU School of Chemical, Biological and Environmental Engineering. “We need technologies that use abundant, inexpensive materials, preferably ones that can be mined in the U.S. This process offers that.”
Most of the thin-film solar cells in use today are made with the relatively expensive compound copper indium gallium diselenide — commonly referred to as CIGS. Indium and gallium are particularly rare and expensive, and are now mostly mined in China — last year, the two compounds were both around 275 times more expensive than the zinc used in CZTS cells. That’s quite a bit more expensive. By utilizing cheaper materials — and ones which could be mined in the US — solar cell manufacturing costs could be significantly reduced.
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The technology being developed at OSU uses ethylene glycol in meso-fluidic reactors that can offer precise control of temperature, reaction time, and mass transport to yield better crystalline quality and high uniformity of the nanoparticles that comprise the solar cell — all factors which improve quality control and performance.
This approach is also faster — many companies still use “batch mode” synthesis to produce CIGS nanoparticles, a process that can ultimately take up to a full day, compared to about half an hour with a continuous flow reactor. The additional speed of such reactors will further reduce final costs.
The performance of CZTS cells right now is lower than that of CIGS, researchers say, but with further research on the use of dopants and additional optimization it should be possible to create solar cell efficiency that is comparable.
“For large-scale industrial production, all of these factors — cost of materials, speed, quality control — can translate into money,” Herman stated. “The approach we’re using should provide high-quality solar cells at a lower cost.”
Funding for this research was provided by Sharp Laboratories of America.
The new research was just published in the journal Material Letters.