The Space Solar Shiel (3S)

Background

As of today, CESI has not yet in its portfolio a product dedicated to the harsh space environment typical of MEO or electrical propulsion-based applications, concerning both the protective coating and the solar cell structure. On the contrary, its European competitor Azur Space has already started the development of a solar cell specifically designed to withstand high irradiation damage.

The developments foreseen in the SpaceSolarShield project aim at filling this gap and possibly at giving CESI a technological edge against its main competitors. Acquiring the know-how and the technological expertise to in-house fabricate its own protective coatings, CESI will gain independency from its present provider of Ce-doped quartz glasses, which are currently produced by the sole manufacturer QiOptiq.

The current situation imposes long, non-negotiable procurement times and a limited choice among a small set of available protective glasses, since the manufacturer does not offer the flexibility to optimize its products for each mission profile and is reluctant in developing new strategies and qualify them. A full manufacturing independence will relieve CESI from such external constraints and will ultimately offer substantial benefits in terms of efficiency of the final product, fabrication costs and both time-to-market and production times.

Additionally, in the case of direct deposition of the protective coating, possibly integrated with the ARC, on top of the solar cells, the whole fabrication process will benefit from an increased robustness and a reduced complexity, not to mention the potential improvement in the exploitation of the available spectrum made possible by removing the UV filter.

Industry Experience

CESI has been involved in the development of high efficiency III-V space solar cells since 1984, and today CESI has a full production line with proprietary technology that covers all the manufacturing steps, up to the solar cell assembly (SCA) of the triple junction cells (named CTJ30). CESI counts more than 100,000 cells manufactured for about 65 civil satellites for over 25 different countries

The so-called III-V based solar cells are currently the most efficient and reliable devices for space applications. Most of the recent satellites are being powered by triple junction solar cells (InGaP/InGaAs/Ge). CESI has been involved in the development of high efficiency III-V space solar cells since 1984, when the first GaAs solar cells flew in space on board of an ESA calibration experiment.

The research and development program has gone through all the steps, from the single junction devices to the multijunction solar cells, and today CESI has a full production line with proprietary technology that covers all the manufacturing steps, starting from the epitaxial growth by MOCVD technology and the post growth processes, up to the solar cell assembly (SCA) of the triple junction cells (named CTJ30). CESI counts more than 100,000 cells manufactured for about 65 civil satellites for over 25 different countries.

Research Team

Marco Beghi, associate professor, Politecnico di Milano: P.I. of the project, responsible for the Politecnico unit;
Davide Loiacono, doctoral student, Politecnico di Milano;
Lia Tagliavini, Politecnico di Milano, expert in communication and dissemination techniques;
Fabio Di Fonzo, Technologist, IIT, responsible for the IIT unit;

Alessandro Mezzetti, post-doctoral fellow, IIT;
Roberta Campesato, Director of Solar Cell Unit, CESI;
Marco Ficcadenti, Responsible of commercial activities for Solar Cell Unit, CESI;
Erminio Greco, Responsible for R&D project inside Solar Cell Unit, CESI.

Partners

The Micro and Nanostructured Materials Lab (NanoLab) of the Department of Energy, Politecnico di Milano, is focused on the nanoscale design, production and investigation of novel materials. Beside film deposition facilities, the NanoLab owns characterization facilities like scanning probe microscopies (AFM/STM/STS) and vibrational spectroscopies (Raman and surface Brillouin scattering).

The Nano2Energy (N2E) lab, of Milan’s Center for Nano Science and Technology (CNST) of Italian Institute of technology (IIT) is devoted to the exploitation of nanostructured materials in the field of advanced energy conversion systems. The N2E lab has a consolidated expertise on the design, set-up and utilization of proprietary custom-crafted experimental facilities for coatings processing, such as Pulsed Laser Deposition (PLD) systems, sputtering sources and ion-beam assisted deposition.

CESI, beside having other fields of activity, is a major supplier of high efficiency space solar cells, which are produced by a proprietary technology, based on over thirty years of research and development.

Technologies

NanoLab, Politecnico di Milano: thermomechanical characterization of thin films: Brillouin spectroscopy to measure the elastic properties, optical implementation of the Stoney technique to measure the thermal expansion coefficient.

Nano2Energy (N2E) lab, IIT: deposition of thin films by a variety of processes, like Pulsed Laser Deposition (PLD), sputtering, and ion-beam assisted deposition. Development of custom-crafted experimental configurations, optimized for specific geometries and/or materials. Thin films characterization techniques like X-ray diffraction.

CESI: a proprietary technology, of the MetalOrganic Chemical Vapour Deposition (MOCVD) type, for the production of the triple junction CTJ30 solar cells. These cells are composed by three sub-cells: InGaP top junction, InGaAs middle junction and Ge bottom junction, connected in series by tunnel diodes.

Skills

NanoLab, Politecnico di Milano: characterization of thin films, by experimental techniques and by numerical modeling.

Nano2Energy (N2E) lab, IIT: optimization of film deposition processes, by the analysis of the relationship between the process parameters and the final properties of the films.

CESI: design of photovoltaic cells by modeling techniques, implementation of production technologies for multi-junction cells and for complete Solar Cell Assemblies (SCAs)

Project activities

  • 1. Management structure and procedures

  • 2. Theoretical analysis of the materials for the optical radiation shield

  • 3. Experimental fabrication and characterization of the selected materials

  • 4. Fabrication scale-up of optical radiation shields as integrated coatings

  • 5. Fabrication scale-up of optical radiation shields as cover sheets

  • 6. Optimization of bare cells for EOL performance

  • 7. Development of SCAs with optical radiation shields as integrated coatings and/or glued cover sheet

  • 8. Preparation of the relevant documentation and of the SCA samples

  • 9. Pre-qualification test campaign samples

  • 10. Post Irradiation Analysis (PIA) of the irradiated SCAs