Silicon (Si) solar cells are of interest for space applications owing to their low cost, material availability, and large production volumes. If their resilience to electrons and protons irradiations was widely studied until the beginning of the 21st century, significant changes in the manufacturing of Si cells have since occurred, improving both the quality of the Si substrates (e.g., oxygen concentration reduction) and the technology of the solar cells (e.g., devices with passivated contacts). Therefore, new challenges recently emerged to understand irradiation-related performance degradations in modern Si materials and cells.

Regarding the behavior of proton irradiated Si solar cells, a consensus is lacking. On one hand, a maximum short circuit current density (Jsc) damage occurring for 1.5 MeV proton energy is shown. Conversely, increasing damage with decreasing proton energy is also reported. This study focuses on modern (i.e., processed via equipment representative of the industrial environment) p-type (Ga-doped) amorphous Si / crystalline Si heterojunction (SHJ) solar cells. They experienced 1 MeV and 3 MeV energy proton irradiations, which produce non-uniform damages within the bulk.

Surprisingly, the Jsc underwent twice more degradation for 3 MeV proton than for 1 MeV proton (for a given fluence), in contradiction with literature. External quantum efficiency (EQE) measurements of 1 MeV proton irradiated devices underlined notably strong variations of the Jsc with the injection level. We assume that these effects may be enhanced by the relatively high resistivity of our sample (60 ohm.cm against 1-12 ohm.cm for the samples from the literature). The solar cells irradiated at the highest fluence 1E14 3 MeV protons/cm2 resulted in device failure. This result – along with EQE shape - suggested a potential carrier removal effect resulting in a type inversion. These effects will be investigated through further measurements after chemical removal of the solar cell active layers.