Alternative TOPCon devices 60 µm thick (size M2)
Crédits : CEA

First TOPCon solar cells adapted for space missions

Research and innovation
Published on 11/27/2023

The two main advanced silicon technologies that are currently replacing the standard PERC cell for terrestrial uses are the Silicon HeteroJunction (SHJ) and TOPCon cells. Both feature passivated contacts and usually rely on n-type silicon substrates.

In space, silicon solar cells suffer from electron and proton radiation induced damages. Use of p-type substrates, front emitters and thin wafers can help to limit this effect. Beyond improving the radiation hardness, thin wafers facilitate design of lightweight and flexible photovoltaic arrays. 

In a recent communication1, CEA showed how SHJ cells can be adapted for space applications. Indeed, by using a gallium-doped (p-type) substrate, the cell features a front emitter. Furthermore, both the cell architecture (symmetric structure) and its fabrication process (low temperature, wafers relying on trays) are compliant with very thin (~60 µm) wafers.

The adaptation of TOPCon cells for space raises more challenges. In this case, with p-type wafers, the cell features a rear emitter. Furthermore, the cell fabrication process is less adapted to very thin wafers (high temperature steps, asymmetric structure). In the frame of the CARLAH project2, supported by the European Space Agency (ESA), CEA is developing an alternative TOPCon device which is designed to be better adapted to space missions.

This alternative TOPCon relies on double-side polysilicon on oxide structures. Ultra-thin polysilicon layers are used to limit optical losses. On the front surface, n-type polysilicon layers are formed. Therefore, with Ga-doped substrates, the cell features a front emitter. Interestingly, this solar cell can be obtained via a lean fabrication process, well adapted to thin wafers.

Recently, and this is a world premiere to the best of our knowledge, CEA successfully prepared 60 µm-thick alternative TOPCon devices (M2 size), by using equipment representative of the manufacturing industry. These devices were electron irradiated and their performances compared to those of conventional p-type PERC. Promising results were obtained since similar post-irradiation PV performances were reached for both technologies, with a device mass about three times lower for the alternative flexible TOPCon cells! These results were presented at the 13th European Space Power Conference (Elche, Spain)3. Several paths were identified for further improving the performances. Stay tuned! 

  • [1] R. Cariou, A. Danel, N. Enjalbert, F. Jay, and S. Dubois, “Investigation of p-type Silicon Heterojunction Radiation Hardness,” 50th IEEE Photovoltaic Specialists Conference, San Juan, Puerto Rico (2023).
  • [2]
  • [3] N. Enjalbert et al., Investigation of thin Poly-Si/SiOx passivated contacts p-type silicon cells radiation hardness, 13th European Space Power Conference, Elche, Spain (2023).

This R&D activity was supported by ESA via a Discovery element contract N° 4000138622. This press release reflects only the authors’ view and not the one of ESA. ESA is not responsible for any use that may be made of the information it contains.

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