Imagine if making solar cells, which harvest light from the sun to produce energy, was as easy as sending this blog post to your inkjet printer. Many scientists, including Chih-hung Chang, professor in the School of Chemical, Biological and Environmental Engineering at Oregon State University, are currently striving to create cheaper solar cells that can efficiently convert sunlight into energy to power our daily habits, and kick our habit of burning fossil fuels. Inkjet printing is in the spotlight as a way to make this goal possible.
One of the greatest barriers to the use of solar cell technology as a competitive alternative energy source to fossil fuels is cost. High costs come from expensive materials and complex traditional production processes required to make solar cells (see image below, conventional process).
Other barriers to cheap industrial-scale production of solar cells include the requirement of toxic or explosive chemicals, vacuum environments, long processing times, large amounts of material waste, and high labor costs of production. This is especially true for the current method of producing thin film solar cells, which harness light-absorbing and light-to-energy converting nanomaterials to turn sunlight into energy.
“We need huge improvements in lowering solar cell manufacturing cost that current [silicon] technology will probably not give us,” Chang said in a 2010 Oregon State University press release.
Chang and colleagues at the Microproducts Breakthrough Institute (MBI) believe they have come up with a new production technique that essentially eliminates material waste, creating thin film solar cells without the need for toxic chemicals or vacuum environments. The process is almost as simple as how your printer patterns ink on a substrate of your choosing. In your case, this would be paper, or if you got fancy, photograph film.
For printing solar cells, instead of using the ink we typically think of, MBI researchers use an ink made out of low-cost and safe metal salts. When the ink ‘dries’, a highly light-absorbing layer is formed on a substrate of glass, polymer, metal or ceramic.
The light-absorbing layer is composed specifically of chalcopyrite nanocrystals, tiny crystals made out of a copper, indium, gallium, and selenium (“CIGS”) semiconductor material. CIGS is especially well suited for the formation of thin film solar cells, because it absorbs light more strongly than the traditional semiconductor that we know so well from the computer industry: silicon.
“Inkjet printing for the solar cell industry is familiar as a method for printing computer data onto white paper and transparent films,” says Dr. Seung-Yeol Han, an MBI researcher who earned his PhD in Chemical Engineering at OSU with Dr. Chang. “Similar to devices used for home desktop publishing, the inkjet-printer actuates well-dispersed nanoparticles … of desired materials in the form of drops of ink from the print head to create [a light-absorbing] film.”
So Chang and colleagues at MBI hope to fabricate thinner solar cells that are competitive with current commercial products, all the while saving precious material resources, time, and money with a now old-hat technology: Inkjet printing.
But Chang and fellow researchers at MBI have taken their ‘inking’ technology even further. They have developed the Microreactor-Assisted Nanomaterials Deposition (MAND) process, a technique similar to inkjet printing that uses tiny pipes to mix materials together and create favorable environments for the formation of nanomaterials. This process allows for stacking of multiple thin nanomaterial layers on top of the CIGS semiconductor layer, further improving the efficiency with which the solar cell converts sunlight into energy.
For example, Chang and colleagues are working on a thin anti-reflective coating that resembles the tiny structures on a moth’s eye. These corneal nipple structures exist in the size range of 1 billionth of a meter, or 10-9 meters. Structures this small interact with light differently that do structures in the macro-world that we can observe with our naked eyes; these structures essentially ‘ease in’ any incoming light, preventing light from being harshly reflected from a surface. For the moth, this anti-reflection property allows the creature to see well at night. For solar cells, a moth-eye-like anti-reflection coating means that less sunlight escapes the solar cell surface by reflection, and thus more sunlight is available for conversion to energy!
Example of an anti-relection coated window – Wiki
Han points out that while many research groups have harnessed biomimicry of the moth-eye to produce anti-reflective coatings, most have produced these coatings using traditional processes for the creation of the nanostructures. “Our anti-reflective coating can be prepared using any existing solution process,” Han said, including a process very similar to inkjet printing.
Han informs us that most recently, his group has achieved an energy efficiency of their thin film solar cells approaching 8% – a current record using this chemistry.
“The most promising thing about inkjet printing is the low-cost nature and high raw material utilization rate of this technology. Potentially, this technology will reduce the cost of manufacture and make solar energy more affordable,” Han said.
Printing our way to a better future.
Inkjet Printed Solar Cells in Other News:
1. Solar Arrays photo by Voice0Reason on Flickr
2. Conventional and Printing Process image courtesy of Dr. Han
Wang, W., Su, Y., & Chang, C. (2011). Inkjet printed chalcopyrite CuInxGa1−xSe2 thin film solar cells Solar Energy Materials and Solar Cells, 95 (9), 2616-2620 DOI: 10.1016/j.solmat.2011.05.011