FEATURE PHOTOVOLTAICS
Killing the battery with indoor solar
We throw away billions of batteries a year. Could low-light solar cells be the answer? Ambient Photonics CEO Bates Marshall explains the technology to Katherine Skipper
A
lthough large, rechargeable batteries used for e-mobility or power-grid storage
get more headlines, we still use a lot of portable batteries for consumer technologies. In 2021, Eurostat estimated that 242,000 tonnes of portable batteries were sold in the EU. Americans purchase nearly three billion dry-cell batteries a year for use in devices such as radios, toys, mobile phones, watches and laptop computers. Battery-powered devices
are often used indoors, where traditional solar cells can’t generate enough power, but Ambient Photonics believes its technology can solve this power shortfall. Its patented technology uses dye-sensitised lasers to build solar cells that remain effective even in low light conditions. Ambient recently announced that Google will be using its technology in a consumer device, with details expected to be announced later this year. Electro Optics spoke to Bates Marshall, Ambient’s CEO, about the technology and his company’s vision for the photovoltaic industry.
What’s the motivation behind Ambient’s technology? I’ve spent the last 20 years working in solar technology but, until I started Ambient, my experience was in traditional outdoor solar. I became interested in solar because it was an opportunity to change the world but, at the same time,
22 Electro Optics May 2024
the success of the outdoor solar industry was leading to a little bit of boredom on my part. It was becoming much more about scaling and a little bit less about invention. I was ready for something else and I was introduced to investors who were funding a project working in low-light indoor photovoltaics. Their idea was that this invention could be a power source for all of the tiny electronic devices that surround us. I got excited about that because it was an opportunity to do something brand new with solar energy and to do good for the planet. Solar-powered electronics
have been with us for decades, but those devices are powered by rechargeable or disposable batteries. Why not use solar cells? To us, the explanation was the lack of power density. If we could increase that, we could become the ubiquitous energy supply for the connected electronic devices that surround us. The devices using this low- light technology would never have to have a battery-replaced or be recharged, and it would eliminate all that toxic waste from batteries.
How does Ambient’s technology work? The technology platform is called the dye-sensitised solar cell or DSC, which was invented about 35 years ago. My co-founder and our CTO, Dr Kethinni Chittibabu, has worked on this for a long time.
Ambient Photonics CEO Bates Marshall
We knew that if you produce photovoltaic technology, which runs very well indoors but is very expensive, it’s not going to be a solution at scale. DSCs promise low-cost production, so we set to work exploiting that while improving the areas in which the performance of the technology was weak. DSCs have an anode and
a cathode, with a liquid electrolyte in between. In our case, it’s two thin sheets of very thin glass with a metallic semiconductor deposited on the glass. We sensitise the semiconductor with our dyes and seal it up with the electrolyte in between. The areas in which we improved the performance were the dyes and the electrolyte; Ambient has invented and patented a number of dye molecules and an electrolyte system.
Ambient has patented more than 40 dye molecules. What do these different molecules do? The spectral distribution of light varies more indoors than outdoors because the light source varies, and the intensity varies more as well. A candlelit room is about 25 lux; a typical
living room at night is maybe 200 lux. Under artificial light, a supermarket might be about 1,000 lux or 1,500 lux. We use the combination of dyes to give us a broad response across varying environmental conditions.
Can you make these devices at scale? Our devices can be made using a production system that is intrinsically low-cost. We don’t have any vacuum processing; there are no clean rooms. We use industrial printing technologies, so we use screen printers and inkjet printers to deposit our materials in standard atmospheric conditions in a manufacturing environment that is clean, but not a clean room. The old tech uses amorphous silicon, and our goal was to match the pricing on a dollar- per-watt level whilst keeping our performance high. We designed and built a fully automated production line. We have a series of machines that are linked by robots and automated guided vehicles that process the entire production flow and, at the other end, we
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Ambient Photonics
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