Solar cells one-thousandth the size of human hair can resist space radiation

Earth's low orbit is filling up, meaning radiation-tolerant cell designs are required as satellites head to higher orbits. Will these new ones do?
Sade Agard
Ultra-thin cells
The cells are the green squares and include an ultrathin layer of light-absorbing GaAs, which is key to their radiation tolerance.

Armin Barthel 

Scientists have developed a radiation-tolerant photovoltaic cell design that features an ultrathin layer of light-absorbing material. According to a new study published today (Nov .08) in the Journal of Applied Physics by AIP Publishing, the devices feature cells with a surface one-thousandth the thickness of a human hair.

Significantly, the ultra-thin solar cells not only surpass earlier suggested thicker solar cells in resilience to irradiation; they also produce the same amount of power from converted sunlight after 20 years of use. Additionally, the novel photovoltaic cells could reduce load and considerably lower launch expenses.

As more satellites head to Earth's middle orbit, they will be exposed to more severe space radiation

It is becoming more and more vital to employ satellites to middle Earth orbits, such as the Molniya orbit, as low Earth orbit becomes congested. However, the proton radiation band around Earth is traversed by this, meaning that radiation-tolerant cell designs will be required for these higher orbits.

Studying distant planets and moons will also require radiation-tolerant cells. For instance, Europa, a moon of Jupiter, has one of the solar system's harshest radiation environments. Therefore, radiation-tolerant equipment will be necessary to land a solar-powered spacecraft on Europa.

The surface of each cell is roughly one-thousandth the thickness of a human hair

The researchers used the semiconductor gallium arsenide (GaAs) to construct two types of photovoltaic devices. The crystal structure GaAs is key to their radiation tolerance. One was an on-chip design created by stacking various materials- one on top of the other.

The surface of each cell is only 120 nanometers thick, or roughly one-thousandth the thickness of a human hair, according to the researchers. This design also involved these cells being bordered by electrically-conducting metals.

The alternative method used a silver back mirror to improve light absorption.

Protons from the Dalton Cumbrian Nuclear Facility blasted two novel types of photovoltaics 

The devices were attacked with protons produced at the Dalton Cumbrian Nuclear Facility in the United Kingdom to simulate the effects of radiation in space. Cathodoluminescence, a method that can estimate the extent of radiation damage, was used to compare the performance of photovoltaic devices before and after exposure.

Additionally, the efficiency of the devices' ability to convert sunlight into power after being hit by protons was tested by a second set of tests using a Compact Solar Simulator.

'The ultra-thin geometries offer favorable performance by two orders of magnitude' compared to thicker devices

"Our ultra-thin solar cell outperforms the previously studied, thicker devices for proton radiation above a certain threshold. The ultra-thin geometries offer favorable performance by two orders of magnitude relative to previous observations," said corresponding author Armin Barthel in a press release.

The authors argue that these ultra-thin cells outperform conventional ones because the charge carriers can survive long enough to flow across terminals in the device.

So, how does being 'thinner' extend a photovoltaic's life?

Most satellites in orbit use photovoltaic cells. When light strikes solar cells, its energy is transferred to the material's negatively charged electrons. These charge carriers are dislodged, creating a flow of electricity over the photovoltaic.

However, space radiation damages solar cells and decreases efficiency by shifting atoms in the material and shortening the lifespan of the charge carriers. Because thinner photovoltaics would mean these charge carriers have less distance to travel throughout their lifetimes, this would equate to extended longevity.

Their outcomes suggest that they could have a point. The researchers found that after 20 years of operation, the new cells, which had approximately 3.5 times less cover glass, delivered the same amount of power as cells with thicker walls.

Still, as with all new technological developments, whether the new cells will progress to scale is another story. IE (Interesting Engineering) hopes to learn more from the researchers themselves- we'll keep you posted.

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