Meet Sol Voltaics and the tandem-junction material the solar industry would really like to use

The biggest challenge with growing III-V materials has been the production costs. Even when using sacrificial wafer substrates, the production costs for PV cells using such materials come in well above commercial cost levels for mainstream terrestrial solar cells. 

Several years ago, a promising technology to manufacture gallium arsenide nanowire arrays by Swedish start-up Sol Voltaics caught my attention. The company didn’t tout big-league conversion efficiencies (15.3% actual) or claim low-cost roll-to-roll capabilities (in fact, they don’t even use a roll-to-roll process). Instead, they touted their in-house Aerotaxy nanowire production method that, if scaled, could dramatically cut production costs and boost efficiencies. 

Ever since my first introduction to the technology, PV Tech has covered Sol Voltaics when it has had something to say. But as with many start-ups, there can be long gaps between announcements, and companies may or may not publicise  breakthroughs or discuss cautious progress toward their commercialisation goals. 

In contrast to those overhyped pesky perovskites, Sol Voltaics’ Aerotaxy nanowire thin-film reactor process and commercial tool development has continued at a relatively brisk pace. The company has maintained its cautious confidence in achieving a production-ready tandem cell that enhances overall module efficiency by more than 50%, which would enable module conversion efficiencies above 27%. 

The nanowires formed in Aerotaxy process are grown in a way that the top and bottom of the nanowire have opposite doping profiles and form a solar cell with p-n junctions found along the length of the individual nanowires. However, the orientation of nanowires can be problematic. But in recent years, Sol Voltaics has developed films (SolFilm) that act as a transfer mechanism and correctly orient the nanowires to be used as a tandem layer and allow them to be transferred to a crystalline-silicon cell. 
 
This is a critical development in Sol Voltaics’ path to commercialisation or at the very least enables the correct alignment of GaAs nanowire film so that solar cell and module producers can evaluate costs and conversion efficiency gains. It’s similar in principle to the likes of Oxford Photovoltaics establishing an evaluation centre to run its perovskite samples on customer cells. 

So how close do I think Sol Voltaics is to its commercialisation goals? 

My best guess would have been three to five years from now. But I’d add a few more years unless a series of publicly issued updates on progress toward commercialisation suggest otherwise. For many other promising start-up technologies, a lack of updates often has meant goals have been pushed out a few more years. When this happens, the companies are usually in no hurry to talk to journalists and discuss their lack of progress. 

So when I was invited to come and see Sol Voltaics’ progress toward commercialisation first hand, I was pleasantly surprised. Not only did the company offer a tour of a newly completed facility built to initiate commercial activities as well as a peek inside its new qualification lab, the trip was only a quick hop, skip and jump from London to Lund University’s technology campus in Sweden. 

During the tour, I was impressed by the scale of the current Aerotaxy chamber (see below). This isn’t a small sample spin-on glass perovskite lab; although the images show only the outside of the chamber, inside it features completely industrial specified components and a pre-volume production layout. The true volume production tool is deep in the design phase, where it is undergoing rigorous design iterations