Low-light photovoltaic cell aims to replace disposable batteries

In conversation with Bates Marshall, co-founder of Ambient Photonics, delving into the firm's purpose to create unlimited power for indoor applications and prevent toxic disposable battery e-waste
Ameya Paleja
Next-generation electronic shelf labels made by Ambient Photonics
Photovoltaic panels are evolving to work at lower and lower levels of light.

Elco van Berkel / iStock 

On average, an individual uses eight disposable batteries every year. This might seem like a small number but scale it up to the population levels of the U.S. and that's three billion batteries. With recycling facilities not accessible in all regions, most of these batteries end up in landfills, damaging the environment.

Ambient Photonics, a California-based startup, is aiming to change this with its low-light photovoltaic cells. For decades, devices like calculators have been equipped with photovoltaic cells, but the energy demands of a calculator are much different from that of many modern-day devices that are equipped with sensors and WiFi or Bluetooth communication technologies.

Ambient's low-light photovoltaic cells are three times more powerful than conventional technology at converting light into electrical energy. The company achieves this with the use of proprietary molecules that absorb light across the spectrum.

The company has partnered with Universal Electronics to replace the disposable batteries in the latter's devices and recently set up a commercial-scale fabrication facility in California.

Interesting Engineering spoke to co-founder and CEO of Ambient Photonics, Bates Marshall. With more than 15 years of experience in the semiconductor and electronics industry, Marshall transitioned to the photovoltaics industry in the solar boom of 2005.

As CEO, he works to transform never-imagined-before ideas into scalable market-transforming products.

Low-light photovoltaic cell aims to replace disposable batteries
Bates Marshall, co-founder and CEO at Ambient Photonics

Interesting Engineering: With countries increasingly building out solar capacity, everybody is focusing on large-capacity cells for solar farms. What made Ambient look for indoor solutions? 

Bates Marshall: Solar farms powered by large-capacity PV cells are playing a vital role in the global transition to clean energy, but they are a grid-scale alternative to using fossil fuels for power generation. Solar farms do not energize devices that rely upon disposable batteries.

To achieve a fundamental reduction in carbon emissions for electronics, solutions like low-light energy harvesting technologies must be commercialized for connected devices.

The sensors, remotes, IoT devices, and other electronics that Ambient cells can power are increasingly ubiquitous and entrenched in our daily lives. Ambient cells provide an alternative power source for these devices and prevent toxic disposable battery e-waste from reaching landfills and leaching into watersheds. 

Ambient is focused on creating unlimited power for indoor applications precisely because the incumbent energy supplies – disposable and rechargeable batteries – have terrible negative externalities. We saw an opportunity to provide a much-needed solution to an overlooked part of the market.

IE: Solar cells for smaller devices like calculators have existed for a long time. How are they different from Ambient's solar cells? 

BM: Solar calculators typically use amorphous silicon PV cells, which do not yield sufficient power in real-world, low-light operational conditions for most IoT and electronic devices. Ambient’s breakthrough PV cells generate more than three times the power of amorphous silicon cells and are produced at mass-market price points.

Low-light photovoltaic cell aims to replace disposable batteries
Ambient's technology was showcased at CES 2023

Ambient cells are the only energy-harvesting technology able to harness photons across the light spectrum, yielding more than 90 percent photon conversion efficiency in low-light conditions.

Due to the indoor light and outdoor low-light environments being dynamic and generally darker than assumed, Ambient’s ability to perform across the spectrum delivers reliable performance in the real world, not just in lab conditions. 

Ambient cells also allow industrial designers to drive PV cell design, rather than the other way around as is typical with amorphous silicon cells.

The company's cells are also made-to-order for high-volume electronic device manufacturers using an industrial printing process that produces cells of virtually any size and shape.

In contrast, amorphous silicon cells require a relatively large, fixed footprint to generate sufficient power. While amorphous silicon cells must be connected in series, a single custom-sized Ambient cell can power an entire device, further simplifying product design and improving aesthetics. 

The performance of Ambient cells is competitive with gallium arsenide, the highest-performing low-light solar technology, which is commonly used on space satellites. Although, it's cost-prohibitive for mainstream applications. 

IE: How has Ambient reinvented the chemistry of dye-sensitized solar cells?

BM: The amount of electrical power produced by a dye-sensitized solar cell (DSSC) depends on how effectively the dye absorbs the photons in the cell. When DSSCs were first developed in the late 1980s to mimic the natural absorption of light energy and convert any visible light – not just direct sunlight – into electrical energy, the power density of DSSCs was not competitive with conventional amorphous silicon solar technology. 

Low-light photovoltaic cell aims to replace disposable batteries
The Eterna remote made for Universal Electronics

Ambient reinvented DSSC chemistry by developing more than 40 new proprietary organic sensitizer molecules. These patented molecules form the basis of Ambient’s proprietary dyes that can absorb light across the entire visible electromagnetic spectrum for the highest possible efficiencies. 

IE: How long did the research take and what were the challenges? 

BM: Ambient Photonics started in 2019 with a group of scientists at the Warner Babcock Institute for Green Chemistry who were inspired by efficient systems found in nature, especially the way chlorophyll converts photons into energy during photosynthesis.

The company's CTO and co-founder, Dr. Kethinni Chittibabu, spent nearly two decades researching printable photovoltaic applications before applying his expertise to Ambient’s uniquely scalable and cost-competitive PV cell printing technology.

The main challenge the team faced was increasing the power density of DSSCs. Low light has fewer photons than direct sunlight by several orders of magnitude, so high power density is necessary to energize modern IoT devices with power-hungry computational, sensing, and communications requirements.

In addition, indoor light sources are varied — a mix of LED, CFL, and incandescent lights are common, plus there is potential for some natural light through a window. Therefore it’s critical for indoor PV devices to harvest equally well under all kinds of light sources.

In general, silicon PV technologies fare much better when high amounts of infrared light are available, which is not the case in indoor settings. In terms of capacity, what improvements can be expected?

In terms of future improvements, our team is hyper-focused on two targets: reducing the production costs of Ambient cells through economies of scale and partnering with our customers on product design.

Since the power density of Ambient’s cells is unmatched in the market, our overarching goal is to facilitate the integration of our cells into end products to drive consumer adoption.

Low-light photovoltaic cell aims to replace disposable batteries
Ambient's mass production facility in Scotts Valley, California

Ambient cells can be optimized to harvest energy from the full range of indoor light sources including compact fluorescent (CFL), halogen, light emitting diode (LED), incandescent, and diffuse or shaded natural light and tuned to maximize performance within a specific device’s real-world operating conditions.

An Ambient cell used in environments with CFL can also be engineered to deliver comparable performance when used in environments with LED light sources. No other photovoltaic technology has this advantage.

IE: Ambient technology has now entered the mass production scale. What is the production capacity and what markets will you serve? 

BM: With the opening of Ambient’s first ‘Fab 1’ factory in Scotts Valley, California this April, Ambient’s technology has officially entered mass production.

Our manufacturing capacity in Scotts Valley exceeds tens of millions of units per year. Unlike expensive semiconductor vacuum manufacturing methodologies, Ambient’s rapid production process is efficient, scalable, and cost-compatible with mass-market electronics manufacturing. 

Low-light photovoltaic cell aims to replace disposable batteries
Ambient's mass production facility in California

There is a tremendously broad array of applications that can be powered with Ambient’s DSSCs. We are initially focused on applications in consumer electronics, smart retail, and IoT (where almost half of IoT sensors are installed inside buildings).

Specific products in these categories include remote controls, electronic shelf tags, and computer accessories like keyboards and mice.

IE: Is this the end of the road for disposable batteries? How will this help the environment? 

BM: Ambient PV cells can make batteries obsolete in many existing electronics, which has two main sustainability impacts: it removes the possibility that those batteries will someday end up in a landfill, and it significantly reduces the carbon emissions of battery-powered devices by as much as 80 percent. 

According to the US Environmental Protection Agency, in the United States alone, approximately three billion batteries are sold each year - that averages to 32 per family or 10 per person. The typical consumer throws out eight household batteries per year. 

Batteries are generating mountains of hazardous waste in landfills, plus the production and disposal of batteries have a large carbon footprint.

Ambient’s low-light PV cells do more to help manufacturers achieve electronic device sustainability goals than any other technology on the market by harvesting energy from everyday light and extending the lifespan or eliminating batteries entirely. IE: What direction is your technology expected to take in the future?

BM: While the applications for Ambient’s technology are broad, opportunities that produce the most significant impact in the shortest period of time currently include battery-free remote controls, PC accessories, electronic shelf labels, and sensors.

Bringing to market high-power low-light solar PV cells at competitive price points not only opens up new sustainability opportunities for device manufacturers but also throws open the doors for design possibilities device engineers cannot achieve with battery-powered devices.

For example, many wall-powered devices draw significant “vampire power” when they are “off.” In many applications, Ambient PV cells can enable true “zero power off” by providing enough power to keep devices online without drawing power from the wall. 

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