INTERVIEWSOLAR JUCTION
performance would enable these manufacturers to cut production costs for systems with a given output power, thanks to the combination of fewer devices, fewer focusing elements and smaller tracking systems.
What’s more, Solar Junction promises to elevate solar cell performance to new levels over the next few years. The current design can potentially produce efficiencies of 44 percent of more, and future variants that do not require any major technical innovation to produce could hit efficiencies approaching 50 percent.
From lasers to CPV
The trailblazing technology that lies at the heart of the Solar Junction can be traced back to James Harris’ group at the Stanford University, CA. Research programmes by Harris and his team include the development of telecom lasers based around the dilute nitride InGaAsNSb . This material system can be grown in a lattice-matched fashion on GaAs substrates, which are cheaper and less fragile than their InP cousins commonly used as a platform for making 1.3 µm and 1.55 µm lasers.
In the mid-noughties, many multi-junction cell developers were trying to fabricate efficient devices that incorporated a bottom junction made from a dilute nitride, which is a strong absorber in the infrared. The Stanford team had a brief stab at this problem, and unlike everyone else, they had some success. They detailed their efforts in a joint paper with NREL.
Harris discussed these promising results at a conference in 2007, and they piqued the interest of Arno Penzias, a Nobel-prize winning physicist
famous for his measurements of microwave background radiation. At that point in his career, Penzias was no longer a researcher – he was racking up ten years as a Venture Partner at New Energy Associates, a major investor in clean technology and a financial backer of the CPV system maker Sol Focus. Penzias was convinced that the Stanford team’s dilute nitride technology could play a major role in accelerating the deployment of CPV technology, and it didn’t take him long to convince NEA to fund a venture to try and make this happen.
A handful of alumni from Harris’ group were tremendously enthused by this opportunity to start a multi-junction solar cell company. Stanford is renowned for fostering a very strong culture of entrepreneurship, and back in early 2007 many of the founders of Solar Junction were working locally for local start-up Translucent. This Stanford spin-off develops interesting epitaxial materials for the electronics, photonics and solar industry.
Defining objectives
On July 16, 2007 three former employees of Translucent and graduates of the Stanford dilute nitride group – Homan Yuen, Vijit Sabnis and Mike Wiemer – co-founded Solar Junction, in conjunction with Harris, Craig Stauffer and Jim Weldon. The latter is a former COO of Translucent, and has 29 years of experience in managing a technology company.
To begin with, the founders of Solar Junction based themselves in Cupertino, which is about a mile from Apple’s headquarters. “We were basically just a bunch of guys cramped into one room, with a couple of laptops and some seed
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www.solar-pv-management.com Issue VI 2011
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