Protecting power for space: advanced cover glass for next-generation solar cells
Powering the next generation of satellites
As satellites become the backbone of global communications, navigation, and Earth observation, the demand for durable, high-efficiency solar power in orbit continues to grow. Harsh conditions — including ultraviolet radiation, atomic oxygen, charged particles, and extreme temperature cycling — threaten the performance of even the most advanced photovoltaic cells.
To address these challenges, SCHOTT, in close cooperation with AZUR SPACE Solar Power GmbH and with funding from the European Space Agency (ESA), developed SCHOTT® Solar Glass exos — a new generation of cover glass specifically engineered for III–V-multijunction solar cells used in Low, Medium, and Geostationary Earth Orbit missions.
This collaboration brings together SCHOTT’s expertise in specialty glass and optical materials with the experience of AZUR SPACE, a 5N Plus company and the European leader and global player in multi-junction solar cell technology. With more than 60 years of experience in high-efficiency solar cells for space applications, AZUR SPACE supported the development and contributed testing and validation to ensure SCHOTT® Solar Glass exos meets the stringent demands of next-generation satellite power systems.
SCHOTT® Solar Glass exos combines optical stability, thermal compatibility, and high scalable production to meet the requirements of next-generation space missions. Specifically tailored with a matching CTE for GaAs-based solar cells, which dominate modern satellite power systems, exos ensures long-term efficiency and reliability across diverse mission profiles — from shorter LEO constellations to long-duration GEO communication satellites.
Key facts
Keeping the lights on in orbit
Almost every space mission relies on solar cells to power satellites and spacecraft. But space is unforgiving: intense radiation, rapid temperature fluctuations in LEO, and the demand for uninterrupted performance push conventional solar cells and their cover glasses to their limits. Ensuring that solar cells remain efficient under extreme conditions and over long-duration missions require an innovative protective solution — one capable of maintaining both performance and stability in the most hostile environment imaginable.To meet their mission goals, next-generation satellites operating in Medium Earth Orbit (MEO) or Geostationary Earth Orbit (GEO) must generate consistent electrical power for 10 to 15 years or more, despite constant exposure to high levels of radiation, intense ultraviolet light, and extreme thermal cycling.
At the core of these power systems are III–V-multijunction solar cells, chosen for their superior efficiency and compact design. Yet, while these advanced cells excel in energy conversion, their surface layers remain highly sensitive to environmental stress. Over time, UV radiation, charged particle impacts, and thermal expansion mismatches can degrade adhesives, weaken interfaces, and diminish power output — threatening the long-term stability of the entire solar array.
The challenge was to create a cover glass that protects solar cells from radiation, UV light, and mechanical stress — while still allowing maximum light transmission and maintaining thermal compatibility with the underlying materials. Most existing solutions force a compromise between durability and efficiency. SCHOTT developed a new material that delivers both lasting optical clarity and mechanical stability for long-term performance in space.
The glass that makes space power possible
With the support of the European Space Agency (ESA), SCHOTT and AZUR SPACE joined forces to develop SCHOTT® Solar Glass exos, an advanced, space-qualified cover glass tailored specifically for AZUR SPACE’s GaAs-based III–V-multijunction solar cells used in demanding orbital environments.At the heart of this innovation lies a composition precisely tuned for optical performance and thermal stability. UV absorption and optical stability have been optimized for long-term exposure, ensuring protection of adhesives and top junctions throughout extended missions. A carefully defined UV cut-off around 308 nanometers filters harmful wavelengths, while maintaining a luminous transmittance of over 91 percent to maximize photovoltaic efficiency.
Its coefficient of thermal expansion, engineered at 6.9 × 10⁻⁶ K⁻¹, is tailored to GaAs solar cells, significantly reducing mechanical stress during the intense temperature swings experienced in orbit. The glass is cerium-doped to enhance UV stability and resist solarization under high radiation doses.
Another key advantage of SCHOTT® Solar Glass exos is its broad scalability: it is available in a wide portfolio of thicknesses and formats, supporting diverse satellite designs and integration needs. This flexibility ensures compatibility across LEO, MEO, and GEO mission profiles — from lightweight, mass-optimized arrays to high-shielding configurations for radiation-intensive orbits.
Exos is undergoing rigorously testing to ECSS-E-ST-20-08C standards, to assess its durability under simulated orbital conditions. Manufactured through SCHOTT’s proprietary down-draw process, it features a naturally fire-polished surface that ensures flawless optical quality and reliable bonding.
Together, these defining features — UV stability, thermal compatibility, and scalability — make SCHOTT Solar Glass exos a space-ready solution that combines efficiency, endurance, and precision. It enables ESA-supported and commercial satellite programs alike to achieve reliable power generation over extended mission lifetimes, while strengthening the European supply chain for critical space power components.
Oliver Theussl
Sales Development Manager