The solar panel above is the first time this author has seen a perovskite+silicon tandem heterojunction module in the real world. It excites me. It should excite you as well.

Oxford PV hopes to deliver perovskite-silicon tandem solar cells to high-end solar module manufacturers in the first half of 2021, now less than a year away. The group expects these solar cells to have an efficiency between 26-27%, and to increase in efficiency by 1% per year as the company dials in the manufacturing techniques. At launch, a 400 watt 60-cell solar module – or a bit greater – will be available. Champion cells from Oxford have long ago hit 28%, with talk of 30% and 500 watt residential modules often.

CommercialSolarGuy spoke with CEO Frank P Averdung, below left, and CTO Chris Case of Oxford PV, to learn about a delicate dance playing out across the North Sea in these times of pandemic.

First, the technology:

Oxford PV is fine tuning the manufacturing of perovskite+silicon tandem solar cells. Here’s Frank Averdung on the timeline for these cells being available to the market:

All of our facilities (in Brandenburg) are in place to accommodate equipment. The initial equipment arrived, and we intend to have this Meyer Burger heterojunction line installed by mid year. The dedicated perovskite equipment will be installed during the second half of the year, with the full line running by the end of the year. By mid 2021, we’ll be at full production.

Oxford PV says at full production capacity they’ll produce 125 MW/year of solar cells. As well, the infrastructure in the Brandenburg facility is enough to quickly double that capacity.

There are currently three ready for consumer heterojunction solar panels on the market – the REC Group Alpha, SolarTech Universal, and the Panasonic HIT. Enel makes a bifacial product that seems only available for its own utility scale projects, while Hevel produces mostly for the Russian and central Asian market.

All of those groups, minus Panasonic, make use of a Meyer Burger heterojunction solar cell manufacturing line. Meyer Burger themselves are so impressed with their heterojunction machines that the company recently discussed moving downstream in the solar market and actually making use of their machines to manufacture solar cells and modules in Europe.

Oxford PV’s secret sauce are the processes and equipment they’ve designed that apply layers of a “wide bandgap perovskite.” Case noted:

It’s just thin layers of perovskite. We’re building an integrated solar cell production line of heterojunction bottom cells, and attaching to that a production line of a couple of additional tools that add these specialized layers. In the end, out comes boxes of standard looking solar cells – but with higher efficiency.

Oxford PV assumes they’ll first sell into the 60 cell residential solar module market. This makes sense as the market does tend to pay more for its modules and seeks higher efficiencies. Do expect it to expand into the white TPO commercial rooftop market and single axis ground mound market, where the product’s very high bifaciality makes it a compelling product choice.

The company says their hardware can adjust to larger sized solar cells now being manufactured. Which fits nicely with another business plan – the integration of Oxford PV machines into already existing heterojunction solar module lines around the world. There is probably at least one company who knows how to sell a few gigawatts per year of this product style.

Oxford’s CEO said the company is ready for a rapid scale up.

Now, the dance:

The teams in Oxford and Brandenburg were separated by a sea, but able to travel back and forth often. At some point, executives put newly hired German engineers in English classes, which caused the English scientists to request German classes. With COVID-19, they’re now of course physically isolated from each other and at a very important moment in the company’s existence.

COVID-19’s need for isolation has led to a restructuring of the Brandenburg solar line assembly group into two independent, never to mingle, teams. The cross trained engineers are concurrently working on both line and process integration.

It was noted though, if the COVID work shut down goes beyond three months, timelines will be stressed. Averdung said:

Things are dependent on each other. First, the facility needs to be ready, we are there. Second, Meyer Burger needs to deliver the heterojunction line, and they have! We are extremely pleased with them, all the tools came in when expected. Another is that the existing pilot line need give enough wafers to build a significant number of modules for pre-certification. Panels must go into testing in Q3. If the pilot line is down, if work stoppages are extended, then that will have an impact.

Oxford says work has slowed a bit, but even with the teams completely avoiding each other, timelines are currently intact.

Perovskite + Heterojunction = ultimate power couple

I’ve commented before on how I believe heterojunction solar cells will be near future of efficiency innovation. It’s not an original idea though, this concept came all the way from the scientists that said a single layer of silicon had a theoretical efficiency limit. As well, in places where cost doesn’t matter – many layered, high efficiency solar products dominate.

The question is – what layers? Gallium arsenide is chosen by many. We know what Oxford PV has chosen, and they see a 37% efficient solar cell in the future. The company says,

It’s very easy to make, and there are multiple ways to prepare. Within our development laboratory we have every competency – spray printing, sputtering, and die coating. No matter what you do with perovskite, you make high performance. In our factory, we’ve chosen the best technique for our product. It is true though that we used to test our solutions on aluminum foil. We’d let it air dry in an hour, then make a test connection – you would see an operating device.

When CommercialSolarGuy visited NREL to write about perovskite – this fast drying was shown clearly. NREL researchers said the product shown in the glass slide below would probably have an efficiency around 15%.