A process known as black silicon can improve the infrared sensitivity of silicon and silicon-based photonics.
Harvard spun out a company called SiOnyx to apply their laser-based black silicon process to imaging and solar. The firm just announced results that demonstrate a 0.3% (absolute) efficiency improvement over standard solar cells.
SiOnyx was founded in 2006 and has taken more than $20 million in funding from Polaris Ventures, Harris & Harris, Vulcan Capital, Coherent, CrossLink Capital, and RedShift Ventures.
The startup uses lasers to texture the silicon surface with nano-cavities which lowers surface reflectance and improves light trapping. More light gets trapped, less gets reflected, and more power gets produced. There are a variety of ways, chemical and physical, to create black silicon, and most solar firms already perform a texturing step on their wafers or cells.
I spoke with Dr. Christopher Vineis, Director of Solar Technology at the startup, and an experienced materials scientist. He cites the benefits of the technology, which include:
- Lower surface reflectance
- Improved light trapping
- Enables migration to thinner wafers while maintaining the same efficiency
- Improvement in process uniformity resulting in tighter binning
All of this can be done while adding one "drop-in" process step using existing equipment. It fits into the solar manufacturing scheme at the end of the wafering process or the beginning of the cell process. It is also complementary with the selective emitter process, which works towards the blue part of the spectrum, according to Vineis.
The question is: is the small percentage gain worth the added expense of the process? In a cutthroat solar economy where cost is king, efficiency often takes somewhat of a back seat.
SiOnyx is not going to be in the business of manufacturing cells. Instead, they look to license the technology to the crystalline silicon solar wafer and module firms. A similar model was tried by Innovalight with their nanoparticle ink, which achieves a similar efficiency boost. Innovalight sold to DuPont in July of this year. SolOptics also has a licensing model in mind for their solar module surface lens technology.