Nanoparticle scattering for radiation-hard multi-junction space solar cells

We investigate how an array of nanoparticles embedded in the anti-reflection coating can improve the radiation hardness of multi-junction space solar cells. In space, high-energy electron and proton radiation reduces solar cell efficiency. Most notably, the InGaAs-middle-cell diffusion lengths are degraded, reducing photocurrent. Metal nanoparticles can scatter incident photons obliquely into the semiconductor, reducing their penetration depths and hence causing charge carriers to be photogenerated closer to the junctions. We postulate that this can improve radiation hardness by improving carrier collection at end of life. In this work, GaInP/InGaAs/Ge solar cells with optimised double-layer AlOx/TiOx ARCs were fabricated with regular arrays of Al nanoparticles deposited on top. An electro-optical simulation tool was also developed, and validated by comparison to the measured quantum efficiency and reflectance spectra, with good agreement. Using the validated simulation tool, we predict the photocurrent before and after high energy electron irradiation. The fraction of the initial photocurrent remaining after irradiation is predicted to improve for certain nanoparticle arrays. However, the overall photocurrent both before and after irradiation is reduced by the presence of the particles. Hence a net benefit is not predicted for the studied array dimensions.