The search for higher efficiencies for silicon-based thin-film is focused on nanocrystalline technology (also called microcrystalline, because of its small crystalline grains), which can be combined with amorphous silicon to create what are known as micromorphous cells; and black silicon, which has low reflectivity. On another front, the dye-sensitized solar cell (DSSC, or Grätzel cell, a type of “organic” solar cell) suggests the possibility of reasonable efficiencies at a low production cost. The DSSC building block is photosensitive nanoparticle dye, which releases electrons that diffuse across an electrolyte to create electric current. Due to the small size of the nanoparticles, the modules can be semitransparent. Potential roadblocks include dye degradation when exposed to UV light and reported cessation of power production at low temperatures if the electrolyte freezes. An interesting facet of this technology is the ability to use colored dyes, which allows printing of solar logos, designs, or even artwork that creates clean energy!
One of the biggest attention-grabbing thin-film companies, Nanosolar, remains focused on large-scale “municipal power plant” installations, not residential roofs. Nanosolar makes CIGS thin-film PV modules, but with a proprietary (and carefully guarded) process: CIGS nanoparticle ink is deposited (through a “printing” procedure) on thin sheets of flexible metal foil, which acts as the conductive bottom electrode. The sheets are cut to size and encased in glass. Nanosolar claims that the proprietary CIGS nanoparticle ink creates just the right mix of the four element nanoparticles (cadmium, indium, gallium, and selenium) and retains that mixture when the ink is printed. Because of claims of up to 14.6% cell conversion efficiency (verified by the National Renewable Energy Laboratory), and also the claim to have the lowest production-cost panel on the market (reportedly less than $1 per watt), Nanosolar has become a media darling. But don’t get your hopes up that you can have the first Nanosolar panels in your neighborhood: Production is sold out for years in advance to large-scale installations, mostly in Europe.