The battery technology that powers space satellites has come a long way, evolving from silver-zinc batteries that lasted no more than 20 days to combinations of solar panels and energy storage systems designed for decade-long operations. Recently, a team of scientists has published a study describing a new solar cell technology suitable for spacecraft applications. Based on polymer compounds and fullerene derivatives, this type of solar cells can sustain the operation of a satellite traveling on a near-Earth orbit for at least 10 years and withstand gamma radiation at levels above 6,000Gy.
About 60 years ago, the Russians launched mankind’s first artificial satellite known as Sputnik 1. This achievement shook the world as radio signals in three frequencies sent from this satellite high above Earth were picked up by monitoring stations around the globe. However, the satellite’s transmitter stopped working in less than a month because the onboard battery that made up the bulk of the satellite ran out of juice. A major lesson learned from Sputnik 1 and other early satellite projects was that a perpetual power source is needed to maintain the vital electronic systems of a spacecraft over an extended period. Subsequently, solar photovoltaics was adopted for the next generations of satellites.
The current crop of silicon solar cells and photoelectric converters used in satellites are mostly composed of materials based on elements from groups 3 and 5 of the periodic table (A3B5). Low energy-to-weight ratio and vulnerability to ionizing radiation have been the persistent issues that impede their progress within this application segment. While advanced encapsulation technologies can protect solar panels from some high-energy particle flows that occur in space, there is still no effective solution to deal with gamma rays that have high penetrating capability. Exposure to gamma radiation will quickly and severely degrade the performance of conventional inorganic solar cells. Specifically, the accumulation of radiation-induced defects in the crystal structure of the silicon material will lead to a sharp drop in conversion efficiency.
The team responsible for the development and demonstration of the new polymer-fullerene solar cells is made up of researchers from the Skolkovo Institute of Science and Technology (Skoltech), the Institute of Problems of Chemical Physics at the Russian Academy of Sciences, and Michigan State University. Previously, another group of researchers led by Skoltech professor Pavel Troshin investigated the stability of lead-halide perovskite solar cells under intense radiation. The result from this study shows that the lead-halide material is still too sensitive to gamma rays and thus not suitable for solar cells used in satellites. On the other hand, the aerospace industry is giving increasing attention to organic solar cells due to their light weight, flexibility, and high energy-to-weight ratio (ranging from 10-20W/g).
Several recent studies have confirmed that certain organic solar cells exhibit a high degree of radiation stability, though the actual mechanism is still less understood. Ilya Martynov, who is the first author of the paper on the new polymer-fullerene solar cells, said that the carbazole-containing conjugated polymers selected for the cell designs have the capacity to ensure a long operation lifetime and “fairly high” conversion efficiency.
The fullerene derivatives that are also incorporated into the structure of the new organic solar cells provide strong protection against gamma rays. These materials allow the solar cells to retain over 80% of their initial efficiency after exposure to gamma radiation at a record-high dose of 6,500Gy. Additionally, fullerene derivatives serve as an excellent electron acceptor in polymer solar cells.
This study on polymer-fullerene solar cells has been published in the journal ACS Applied Materials & Interfaces. Its findings raises the possibility of power solutions for satellites that are more stable, more efficient, and longer-lasting. Organic solar cells, which weigh less than conventional silicon-based counterparts, also help lighten the satellite payload and thereby lowering the rocket launch cost.