A major breakthrough for photovoltaic technology in space.
The CEA has developed high-performance thin silicon solar cells for space applications. We have also demonstrated a process that enables these industrial-grade cells to be radiation-resistant in orbit.
Since the 2000s and what has been called the “new space” era, the space sector has been going through some big changes. The need for bigger volumes and lower costs for solar arrays that power communication satellite constellations has put silicon back in the spotlight.
Silicon photovoltaic technologies are not new in space. They were even used right from the start, with the Vanguard 1 satellite in 1958, up to the largest photovoltaic installation in orbit, that of the ISS, the International Space Station. They were later gradually replaced by III-V cells, which offer better resistance to radiation and superior performance and longevity in the space environment. However, III-V cells are much more expensive and production capacities are limited.
Silicon photovoltaics for terrestrial applications have since been widely developed at a rapid pace. With better efficiency than in the past, very low-cost cells and numerous manufacturing facilities, they are once again becoming a good candidate for meeting the challenges of modern space exploration.
The CEA at INES, with support from CNES through its R&T programme, and then through technology development for Telecom projects (PEGASE programme), is enabling the creation of a European industrial sector for heterojunction cells on thin substrates (≤ 90 µm), which are effective for space applications.
One of the challenges is, obviously, photovoltaic conversion efficiency, which must be guaranteed throughout the satellite's lifetime, despite degradation caused by irradiation from high-energy particles.
In low-orbit space conditions, with an AM0 spectrum (Air Mass 0 - i.e. the solar spectrum in the absence of the atmospheric filter) and electron irradiation doses of 1 MeV at a dose of 1014 e-cm², the conversion efficiency of our 90 µm thick heterojunction cells has been measured and certified at over 14%. The irradiation tests, simulating the dose received in orbit, are carried out on Earth using the SIRIUS platform's electron accelerator and the expertise of the LSI, the irradiated solids laboratory at CEA IRAMIS.
A 14% efficiency after irradiation is an excellent result, which already allows for demonstrations and applications in real conditions, in space, for industrial technology.
We call self-curing the phenomenon that gives cells the ability to better resist radiation and maintain their initial performance under operational conditions. To achieve this, the CEA has developed and patented a silicon treatment process that enables the cells to exploit the light and heat found in space to maintain their full performance.
We have demonstrated that this process enables photovoltaic cells exposed to the space environment to recover from damage.
The demonstration was carried out on cells representative of the terrestrial photovoltaic industry, with thicknesses of 90 and 60 µm. Cells irradiated with electrons at a fluence of 10¹⁴ cm² recover 97% of their initial performance! This result has been certified by the independent organisation Caltec (ISFH) under representative operating conditions (80°C).
Credits: Crédit L. GODARD / CEA