What is silicon ink? Is it magical pixie dust? Innovalight, maker of silicon ink, is a venture capital-funded company in Silicon Valley that was just acquired by DuPont. The announcement came Monday and I’ve been wanting to post about it but a small problem held me back.
I had no idea how Innovalight’s product works. I knew what it is though – it’s ink (and it sure looks like ink) made up of silicon nanoparticles suspended in chemicals. It can be screen printed in the same assembly line used to manufacture crystalline silicon solar cells.
The reason a manufacturer would add this extra step is simple. It increases the cell’s ability to capture energy from sunlight by 1%.
Since Monday I’ve learned a bit more – enough to burden blog readers with my still incomplete understanding. Adding a precision-printed design of this ink to crystalline silicon solar cells allows the cell to capture more energy from the blue wavelength of sunlight. This sentence is where I would describe exactly how the ink makes that happen, so let’s pretend I did that.
Solar cells are generally hampered in their efficiency by an inability to capture energy from the full spectrum of light. Like the human eye, they do best capturing visible light. But that leaves a wealth of radiation in the UV and infrared part of the spectrum un-captured. Thus the 19% upper limit on even very efficient cells.
Interestingly, even within the visible spectrum, blue light is not well captured. My colleague Mitch Jacoby tells me that blue light is energetic enough for a solar cell to absorb and create a flow of energized electrons, but that the high energy electron and the “hole” left behind re-combine before they hit the conducting grids and without creating a current. Many people in many places like NREL have been studying ways to keep them separated and have them move to the negative and positive current collectors.
That’s why the DuPont press release about the acquisition talks about Selective Emitter solar cells. In spite of the capitalization, the term seems a bit misleading to me, because absorbing is what they’re going for. Anyway, selective emitter approaches involve an adaptation to the silicon, the surface and/or the conducting grid to make those electrons from the blue light migrate efficiently.
Innovalight’s value proposition is that solar cell manufacturers can make selective emitters in their current process by adding a silicon ink screen printing step after texturing the mono crystalline silicon.
According to the press release, “Selective Emitter technology could represent 13 percent of crystalline silicon solar cell production by 2013 and up to 38 percent by 2020.”
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