This week we had a catch-up with the world’s only commercialized perovskite solar manufacturer, Saule Technologies. Though Saule emphasizes devices, the major avenue for that commercialization at present is a 1-year trial which began in 2021 with Aliplast, an aluminum profile and frames manufacturer. Once the results come in from the perovskite sun-blinds installed at an Aliplast facility, the two companies will offer such installations as a product to Aliplast’s customer.
Saule Tech’s David Forgacs, Director of Knowledge Management, calls this BAPV (Building Applied Photovoltaics), as opposed to BIPV (I for integrated), because it’s something which can be applied to an existing element of a building. But when talking about this product, Forgacs immediately mentions that Saule Technologies has faced issues scaling up its production due to a lack of finance, which means the company’s strategy will also be pursuing smaller-scale device applications such as solar-powered price tags. When we last spoke to Forgacs almost two years ago, he said the company was pursuing a cautious strategy of low costs balanced by getting revenues online as early as possible, and clearly nothing has changed in that regard.
At present the company’s manufacturing line is 40,000 square meters, around 4 MW production capacity, with much of it reserved for R&D. Only in 12 months is the company’s second production line due to be completed – if all goes well with the equipment and component supply chain. That second production line, which has a completed design, will be 20 MW to 30 MW, with a further 100 MW production line to be operational in 2024 to 2025, ideally. That would be enough to have a small residential supply business.
Two years ago the company was hoping to reach that 100 MW in 2022 to 2023, so it really has stalled on the production front – but at least it hasn’t had a total falling-out with its equipment suppliers as Oxford PV has, and since 2020 it has become the sole commercialized perovskite company, on however small a scale. Another way it has made progress is R&D, with staff reaching 70 in number, of which 50 are technical. Its indoor perovskite product reaching 20% efficiency, a big improvement over the past 10%, which is still where the company’s outdoor perovskite is at.
At the 1 cm2 test cell scale, the company reached 25.5% in October and should soon present an over 30% efficient test cell at a conference. The 25.5% value would be behind its rivals while the latter would be a world record, but it is something of an apples to oranges comparison because this is specifically low-light performance. But Forgacs assures us that the over 30% result will be a record for perovskite on a flexible substrate – exceeded only by results found using glass or smaller areas.
So the test cells are, as before, 10% higher efficiency than the main production cells, but 30% and 20% is a lot better than 20% and 10%. Asked about the relevance of a 1 cm2 test cell to a full-size product, Forgacs states that the size is equivalent to one cell in a module, and that many test cells people write about are much smaller than that. In fact, Saule’s price tag offering is only 10 cm2 per module, while some enquiries involve complete modules which are only 2 to 3 cm2 in size. Deformations are not the only cause of lower efficiency in larger offerings – there’s also the sheet resistance of the electrodes. In silicon PV, test cells are only 2% more efficient than the best commercial offerings.
Asked about the research used to improve indoor performance, Forgacs stated that shunt resistance and uniformity of layers becomes much more important, while sheet resistance is less important, due to the low charges involved, given that indoor irradiance is less than 1% of the outdoors. As for the perovskite formula itself, Forgacs states that it is changing up the additives and solvents, but that for the foreseeable future it will continue to be a lead-based formula – tin-based and other alternatives remain significantly lower performing.
Asked what the main research challenges are, Forgacs describes a multi-directional balance which must constantly be struck between production cost, stability, and efficiency – post-treatment, avoiding defects, and the annealing process can all be hastened, but it risks a loss of efficiency and stability – an over-hasty annealing process can cause damage. A few years ago Saule switched to using carbon-based electrodes for opaque modules, which is good for stability and cost, but is a much thicker layer than the rest of the device. A thinner, more flexible device loses conductivity, incurs higher sheet resistance, and loses performance. So Saule is trying to enhance such a thinner device with different additives and other measures to maintain good conductivity.
Another technical challenge is semi-transparent devices – a category which would requires millions of dollars of investment into the machinery for large scale manufacturing. Packaging is another part of new research – Saule is developing an inhouse solution which should be ready in two years. Then there are outdoor products, which will each have to have their own certification, as will the solar blinds – Saule Technology can offer a lot of different customized products, but the certification system with its 8 month wait periods is an obstacle when that variety requires equally as many certificates.
The three-way quandary of stability, cost and efficiency is simplified with indoor installations, which are exposed to far fewer extremes of humidity, heat, or light, removing stability from the equation, while efficiency can reach 20% with indoors light, because there is no infrared or ultraviolet, and the perovskite can be designed around capturing a narrower spectrum.
This brings us to Saule Technologies’ second commercial product, launched in November, which is electronic price tags, properly called Perovskite Electronic Shelf Label (PESL). Here Saule is running into stiff established competition, and looks most likely to find a niche as a more expensive but more powerful system, which can change the display eight times a day instead of twice – something that will be useful if the shop brings in a dynamic pricing system for things such as shortages and expiry dates. More power also means less battery use and replacement, and potentially a longer lifetime before power output drops too low – with further testing Saule’s PESL product should reach a 10 year lifespan, compared to the usual 5 years. These indoor solar price tags will need an inbuilt power system, but that’s only a matter of added price – it isn’t obtrusive, unlike a connection to a rooftop solar installation.
Saule Technologies still employs sheet-to-sheet inkjet as its production technology, but as the company looks to expand its output, it is now pursuing the roll-to-roll method for its second production line. The position that Forgacs communicates is he expects both methods to be used for the foreseeable future. Initially sheet-to-sheet will remain the primary focus, with the roll-to-roll line being useful for comparison. As times goes on roll-to-roll will come into its own thanks to higher volume of output, especially with agreed-upon form factors and improvements to smooth coating, but sheet-to-sheet will always be more easy to switch between designs for different clients, making it the preferred choice for Internet of Things (IoT) device offerings. while roll-to-roll will be preferred for BAPV and other larger-scale products.
We haven’t heard of any other company selling perovskites so far, though Caelux in the US is very close. The most famous Western company, Oxford PV, is still obstructed by its fall-out with Meyer Burger on its tandem production line. In China the giant battery manufacturer CATL, which was hiring R&D researchers in 2020, announced this week that it would build a pilot production line for perovskites. In the past two years perovskites have not made the rapid progress towards commercialization which we hoped for, and even the tandem technology which it was expected to use, is going to enter the market with First Solar and Sunpower’s Si-CdTe tandem instead in about two years. But perovskites still have the same promise they always did, and it is still attracting new backing. We can confidently say that it will play a significant role in the future.
Forgacs credits Saule Technologies’ ability to proceed where others have not to the company’s emphasis on indoor device products. We expect the next steps made by other companies to be similarly “humble” options, such as selling perovskite-coated solar module glass coverings to be combined with silicon PV by module manufacturers in a manner that keeps the two semiconductors separate at the cell level, which is what Caelux does.