The US Patent Office has issued US Patent No. 8,859,310 to Versatilis LLC of Winooski, VT, USA (a technology and business development firm that focuses on novel materials and processes for electro-optical devices, as well as extending its Versulite brand of 2D layered materials). Versatilis commercializes technology by licensing and partnering with others, or by setting up separate focused subsidiaries (e.g. VerLASE Technologies, launched in 2013 with an investment by Wakley Ltd, to focus on laser-based light sources in the visible).
The new patent shows how fine semiconductor particles (powders or fines, which are widely available either readily synthesized or often a waste byproduct of processes such as dicing wafers into ever smaller chips) can be processed into low-cost solar cells or micro-LEDs.
A principal challenge in making such devices has alwcays been forming the active layer (the light absorbing layer in a solar cell or the light-emitting layer in an LED). This has also been the most costly and capital-intensive part of the manufacturing process, as it must be made to high standards of crystal quality and uniformity, e.g. leading solar cells use mono- or polycrystalline silicon wafers while LEDs use variants of gallium nitride (GaN) on expensive sapphire, silicon carbide (SiC) or even GaN wafers. In many cases, these materials are thicker than needed - the added thickness lends structural support to the end device without adding to efficiency, but contributes to overall cost and weight of the structure.
Versatilis says that, instead, it has shown that the active layer can be made from semiconductor fines or powders of single-crystal particles by rapid deposition as a closely packed monolayer, and then further processed into functional active diode structures (solar cells or LEDs). Such particles are readily available, often as a byproduct of other processes or made inexpensively off-line, or sometimes chemically synthesized. For example, silicon fines are widely available (screened for a desired size distribution), as are copper indium gallium diselenide (CIGS) and GaN particles (the latter chemically synthesized). Also, a small amount of such ‘dust’ can go a long way (e.g. a kilogram of 1 micron single-crystal CIGS particles used as micro-solar cells can cover an area over 300m2, 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 optoelectronic devices with reduced infrastructure, processing, and material utilization cost,” says chief technology officer Ajay Jain (inventor of the now patented technology).
Versatilis says that the potential cost savings have led others to try using semiconductor particles in various ways, but none have proven commercially practical. A major challenge has been to deposit the 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 the nanoscale, including suitable tools for in-line process metrology and characterization, says the firm.
In addition to processing semiconductor particles into useful devices, Versatilis says that it 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. The firm has licensed the technology to VersufleX Technologies LLC, which is beginning to sell benchtop process tools to R&D labs. The process can tolerate reasonable variation in particle size and shape, and various methods are 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,” says CEO George Powch, “It can enable low-cost building-integrated photovoltaics or rival OLEDs with a wholly inorganic large-area micro-LED solution,” he believes.
