Ultra-thin heterojunction photovoltaic cells for space

Since the early 2000s, the space exploration field has been changing. We speak of "new space": the shift from a government-led agency initiative to a private initiative industry seeking low-cost access to activities in space.

The race to lower costs for space-based solar generators (constellations) and for upper atmosphere photovoltaic applications is now on.

Silicon photovoltaic technologies are not new in this field. They have enabled the development of the space conquest, from the Vanguard 1 satellite launched in 1958 to the largest photovoltaic installation in orbit: the International Space Station. At the beginning of the 21st century, cells based on III-V materials have replaced them, gradually becoming the premium reference in this industry. These III-V cells offer higher performance and longevity in the space environment.

Silicon photovoltaic continued to develop at an accelerated rhythm on earth with: exponential production volumes, a drastic decrease in costs, a significant improvement in conversion efficiency, industrial maturity, etc.

Today, with the growing need for low-cost photovoltaic power for low-earth orbit satellite constellations, silicon photovoltaics is logically back in the spotlight.

To take advantage of advances in terrestrial photovoltaics, the challenge is to smartly adapt these silicon technologies for space and/or the stratosphere. The menu includes cell thinning, minor modifications to the architecture and manufacturing processes, with the aim of increasing resistance to this specific environment (irradiation, UV, extreme temperatures).

In this context, and with the support of the French space agency CNES, the CEA at INES is studying and developing modern heterojunction silicon cell technologies for space applications. Promising results confirm the relevance of this approach: ultra-thin cells (60µm, i.e. the thickness of a hair) combining mass gain (they are three times lighter than the standard) and flexibility, have been produced with terrestrial photovoltaic production means.

The performance of these ultra-thin heterojunction silicon cells is excellent, with a conversion efficiency of 22% measured under AM1.5g spectrum. Space environment resistance tests are underway, as well as the next developments to make these cells even more robust. Stay tuned ;)