Lightweight Organic Solar Cells Could Be Game Changer for Space Flight

This image is a schematic overview of the MAPHEUS-8 sounding rocket flight. In the foreground on the left, the experimental setup, highlighted in gold, is part of the payload. Eight symmetrically arranged hatches contain each one organic (green) and one perovskite (brown) solar cell module. Neighboring hatches contain different cell types indicated in different colors. The background shows the suborbital parabolic flight trajectory with the apogee reaching into altitudes common for low-earth orbit satellites. (Reb et al. / Joule)

(CN) — Scientists recently tested a pair of novel solar cell technologies during a brief suborbital space flight and found they hold promise to transform the way electronics and propulsion systems are powered in orbit and beyond.

Mass is of paramount importance when trying to escape Earth’s gravity well. It costs about $2,500 per pound to place something in orbit with a reusable rocket, so every ounce shaved is crucial. This means the key metric for evaluating space-bound solar cells is power density — the power output generated by the cells, divided by their mass.

Researchers detailed the first in-space test of perovskite and organic solar cells in a paper released Wednesday in the journal Joule. The rocket carrying the cells launched from Sweden in June 2019, reaching an apogee of 149 miles where its cargo performed admirably throughout the seven-minute test flight.

The team led by senior author Dr. Peter Müller-Buschbaum, professor of experimental physics at the Technical University of München in Germany, compared these new solar cell technologies with traditional nonorganic silicon-based models. They also sought to gauge how well the new cells hold up under the punishing vibrations, g-forces and radiation inherent in space flight.

“We report the first in-situ demonstration of functionality and power generation under space conditions for perovskite and organic solar cells. So far, both types of cells were only tested under terrestrial conditions,” said Müller-Buschbaum in an email interview.

“The rocket was a big step,” added first-author Lennart Reb. “Going to the rocket was really like going into a different world.”

Specific power — the amount of electricity produced by weight — is more important than efficiency for operating in space, according to Müller-Buschbaum. The researchers were able to test both perovskite and organic cells under multiple lighting conditions thanks to the rocket’s differing orientations during flight. The new cells demonstrated their potential to outperform silicon-based varieties under strong illumination and continued generating power even once the available light began to drop off.

“Transferred onto ultra-thin foils, one kilogram (2.2 pounds) of our solar cells would cover more than 200 square meters (2,153 square feet) and would produce enough electric power for up to 300 standard 100-W light bulbs,” said Reb in an accompanying statement. “This is 10 times more than what the current technology is offering.”

The cells also generated power under weak lighting conditions — similar to those found in deep space — opening the door for more power-intensive missions to our outer solar system and beyond. To date, most deep space missions have been powered by tiny nuclear reactors called radioisotope thermoelectric generators, which present their own set of challenges and drawbacks.

“We were able to show the solar cell operation under diffuse terrestrial irradiation (without direct sunlight), which is exciting for deep space missions and will require more attention how to optimize solar cells for such kind of missions,” said Müller-Buschbaum.

Rigidity is another important factor for space-bound hardware. Modern silicon solar panels are thick and heavy. They’re folded up like orbital origami prior to launch, and it’s not unheard of for a panel to hit a snag during its unfurling, often with disastrous results for the mission. Payload adapters are round, so a round payload is probably ideal. Their wet-chemical processability allows perovskite and organic cells to be deposited onto flexible and foldable lightweight polymer foils.

The new cell types are also cheaper and less energy-intensive to build than traditional cells by employing additive deposition techniques such as inkjet printing and spin coating. Traditional solar cells are manufactured in expensive clean-room facilities under high heat and vacuum, which perovskite and organic photovoltaic cells do not require.

In recent years these new cells have reached increasingly impressive operating efficiencies, topping 25% and 17%, respectively, narrowing the gap with traditional solar cells. The authors say the next step is to test them on longer duration flights, such as an orbital satellite, to better understand how they hold up and perform over time.

“It’s the very first time these perovskite and organic solar cells ever were in space, and that’s really a milestone,” said Müller-Buschbaum. “The really cool thing is that this is now paving the way for bringing these types of solar cells to more applications in space. On the long run, this might also help to bring these technologies for broader use in our terrestrial environment.

“It is very exciting to have both novel solar cell technologies on the next step to make them used in space missions.”

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