Many modern satellites use solar cells to continuously harvest energy from the sun, allowing them to power their electrical circuits without significant battery storage. Yet in the harsh environment of outer space, unprotected by Earth’s atmosphere, these materials are also vulnerable, especially to solar radiation, in the form of high-energy protons and electrons from the sun. .
The challenge: When semiconductors in solar cells are bombarded with these particles, their atoms, arranged in ordered crystal lattices, are displaced, disrupting their ability to convert incoming sunlight into electricity.
Over time, this will gradually degrade cell performance, eventually killing the satellite.
The extent of this damage can vary greatly. While the radiation isn’t too severe at low altitudes, where most satellites currently reside, they are much more vulnerable in medium Earth orbit, where a belt of high-energy protons from the sun have been captured by Earth’s magnetic field. This is a growing problem as low Earth orbit becomes increasingly crowded with satellites.
It also presents a challenge for more distant missions to other planets and moons. For example, Jupiter’s moon Europa is one of the most studied targets for future missions, as many astronomers consider its vast subterranean ocean to be one of the most likely environments in the solar system to potentially harbor a extraterrestrial life.
However, since Jupiter bombards Europa’s surface with some of the strongest radiation in the solar system, satellites orbiting the moon would be particularly vulnerable.
Less is more: Surprisingly, the key to stronger solar cells may be making them thinner.
Physicists have recently made progress towards solar cells a few tens of nanometers thick. When exposed to solar radiation, high-energy protons and electrons are more likely to simply pass through these materials, never interacting with the atoms in their ordered crystal lattices.
Yet, before ultra-thin solar cells can be used to power satellites in future space missions, researchers will first need to establish robust techniques to test their performance when exposed to harsh radiation. Thanks to a new study published in the Journal of Applied Physics, a team of British researchers has taken promising steps towards such tests.
The key to stronger solar cells may be making them thinner.
The experience: Led by Armin Barthel at the University of Cambridge, the team’s experiment focused on gallium arsenide (GaAs): a semiconductor that can be fabricated with a thickness of just 80 nanometers, and is currently considered one of the most promising materials for use in ultra-thin solar cells.
Their study considered two possible designs: one featuring multiple stacked layers of GaAs; and the other containing a single layer, lined with a silver mirror to enhance its light absorption.
Using state-of-the-art facilities, the researchers first irradiated GaAs solar cells just 80 nanometers thick with high-energy protons, at an intensity similar to the radiation experienced by real satellites.
They then used a specialized electron microscopy technique to map the resulting displacement of the atoms from their original lattice arrangements. At the same time, they subjected thicker, more conventional solar cells to equally harsh treatment.
Along with this experiment, Barthel’s team measured the difference in power generated by each type of solar cell, both before and after being irradiated. They found that the resilience of GaAs solar cells meant that even when the area they covered was 3.5 times smaller than the thicker materials they were studying, they had to deliver the same amount of energy over a period of 20 years.
More resilient satellites: If this performance could be maintained in real satellites, it would not only extend their operational lifetime, but their reduced weight would also require less energy for launch, making these future space missions less expensive and more efficient.
Building on their techniques, Barthel’s team hopes that researchers in future studies can reliably examine and compare the performance of ultra-thin solar cells with even more advanced designs.
This could ultimately lead to new generations of more resilient satellites, potentially opening up the vast regions of Earth’s mid-orbit to more satellite operations. As low Earth orbit becomes increasingly crowded, this could ensure that critical satellite applications, including navigation, communications and weather forecasting, can continue to progress and grow.
Elsewhere, the team’s techniques could lead to space probes better suited to exploring more distant regions of our solar system – helping astronomers answer some of the most pressing questions about our solar system, such as whether life could really be out there on worlds like Europe.
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