The U.S. Patent Office has issued US Patent No. 8,859,310 to Versatilis LLC that shows how fine semiconductor particles, powders or fines, often the waste byproduct of dicing semiconductor wafers into ever smaller chips, can be processed into a sea of low cost solar cells or micro-LEDs.
A principal challenge in making such devices has always been forming the active layer, whether the light absorbing layer in a solar cell or the light-emitting layer in a LED. This has also been the most costly and capital-intensive part of the manufacturing process, since the active layer must be made to high standards of semiconductor crystal quality and uniformity. Leading solar cells, for example, use mono- or poly-crystalline silicon wafers, while LEDs use variants of Gallium Nitride (GaN) on expensive sapphire, Silicon Carbide or even GaN wafers. In many cases, these materials are thicker than needed, the added thickness lending structural support to the end device without adding to efficiency, but contributing to overall cost and weight of the structure.
Versatilis shows instead that the active layer can be made from semiconductor fines or powders of single crystal particles densely packed into a monolayer, in a configuration not unlike sandpaper one particle thick, and then further processed into active diode structures serving as solar cells, for example, or as LEDs. Such particles are readily available, often a byproduct of other processes or made inexpensively off-line, or sometimes chemically synthesized. Silicon fines, for example, are widely available, screened for a desired size distribution, as are CIGS and GaN particles, the latter chemically synthesized. And a small amount of such “dust” can go a long way; for example, a kilogram of one micron single crystal CIGS particles used as micro-solar cells can cover an area over 300 square meters, resulting in very low costs per unit area.
“By levering cheap, ex-situ produced and optimized, single or polycrystalline powders and fines for Si, Ge, CIGS, GaN, ZnO as the starting raw material and wrapping unique processing techniques around that, we can produce highly functional opto-electronic devices with reduced infrastructure, processing, and material utilization cost,” stated Ajay Jain, Versatilis CTO and inventor of the now patented technology.
The potential cost savings have led others to try using semiconductor particles in a variety of ways, however, none have proven commercially practical. A major challenge has been to lay down these particles quickly enough and as a monolayer. Similarly, researchers have shown basic functional devices with nanorods, nanowires and other semiconductor “nanostructures” in the lab, only to be stopped by a general lack of production ready manufacturing technology for nanoscale, including suitable tools for in-line process metrology and characterization.
In addition to processing semiconductor particles into useful devices, Versatilis has unique fluidics technology for rapidly depositing such particles as a monolayer, from nano to microscale, on wafers or in a continuous, high-speed web. It had licensed the technology to VersufleX Technologies (http://www.versuflex.com), who are beginning to sell benchtop process tools to R&D labs based on this technology. The process can tolerate reasonable variation in particle size and shape, and there are a variety of methods possible for orienting particles floating on the surface of a fluid medium.
“This technology will not set performance records for efficiency in PV cells nor in lumens/watt for LEDs, but we believe there is no cheaper, more practical way to realize semiconductor diode based functionality over a large, flexible area,” added George Powch, Company CEO, “We think it can enable low cost Building Integrated Photovoltaics or rival OLEDs with a wholly inorganic large area micro-LED solution.”