Swedishsolarmaterials startup Sol Voltaics just announced a $12.5 million Series C investment for its gallium arsenide (GaAs) nanowire technology.

The company is attempting to commercialize a radically different solar technology -- its GaAs nanowires are tiny solar cells about 1 or 2 microns long and approximately 100 nanometers in diameter. They're sold as an ink-like solution that is applied to create an absorber layer on top of existing solar cells that "capture light very effectively on top of panels using a phenomenon called wave-concentrated photovoltaics (WCPV)," according to the company.

Meant to be integrated in a tandem-junction architecture on mainstream crystalline silicon panels, Sol Voltaics’ nanomaterials are claimed to boost photovoltaic module efficiencies by more than 27 percent. This suggests that a 17-percent-efficient crystalline silicon panel has the potential to reach 22 percent efficiency with the addition of the nanowires. Sol Voltaics has demonstrated a 1-sun conversion efficiency of 15.3 percent in a GaAs nanowire array solar cell, as verified by Fraunhofer ISE.

The funding round was led by new investor Riyadh Valley Company, the VC arm of King Saud University. Existing investors Umoe, FAM, Industrifonden, and Nano Future also participated. In total, the company has raised more than $25 million in equity and grants.

Sol Voltaics uses a process invented by company founder Lars Samuelson called Aerotaxy to grow the nanowires, described in Nature in December 2012 as the "continuous gas-phase synthesis of nanowires with tunable properties."  

According to the firm, "Nanowires and nanotubes are typically produced through an epitaxial process, that is, they are slowly grown as crystals in low-pressure/high-temperature environments on silicon or sapphire substrates. Because of the inherent physical limits of the epitaxial process, nanoparticles often need to be grown in place or harvested and sorted in batch processes that can be both time-consuming and expensive. Aerotaxy creates nanomaterials by suspending active materials in gases intermingled in a precisely controlled environment."

Less than a gram of solution of nanotubes is poured or printed on an existing solar cell (the ink needs to cover only 12 percent of the solar cell), then the nanotubes are aligned and fixed with a polymer, upon which a transparent conductive oxide is layered. Sol Voltaics recently announced what it referred to as "a major technological breakthrough" with the alignment of gallium arsenide nanowires in a thin film.

Once you have this magic sauce, you have to sell it -- and that leaves the task of selling to Chinese panel manufacturers such as Trina or Canadian Solar. Sol Voltaics' process requires integration into gigawatt-scale production sites, as well as capex investment in more equipment to apply and set the nanowires. The value of improved efficiency is evident, but this remains a challenging customer base.

Winning early-stage venture funding for a solar module hardware/advanced materials effort is a notable event these days -- and it's still early for this company. But radically new material systems tend to take longer than planned to develop and commercialize.

All the while, incumbent solar module firms such as LG, SunPower and First Solar, as well as aspirants such as Suniva, Silevo and Solexel, are also driving toward higher efficiencies at lower costs. SunPower's X-Series panels are 21.5 percent efficient. Average cell efficiency across all SunPower lines was close to 23 percent in late 2015, according to the company. 

The startup is a sister company to LED nanowire firm Glo.