Radiation-induced effects in solar cells for future space missions: a combined Monte Carlo and ab-initio study of proton impact, electronic stopping and threshold displacement energy

Solar cells in space are degraded mainly because of atomic displacements induced by radiation (protons, electrons …), in particular in the regime where the Non Ionizing Energy Loss (NIEL) [1] of the impacting particle is transferred to such displacements via Coulomb interaction. The NIEL is generally calculated via the Monte Carlo binary collision approximation, without considering crystalline order and the coupling between ionic and the electronic degrees of freedom. Here, after analyzing the energies of protons passing through triple-junction solar cells in a realistic space scenario via Monte Carlo particle transport, we present an ab-initio study on a) the real time dynamics of the electronic stopping for protons passing through the thre layers of the cell [2]; b) the sensitivity of the minimum energy to create a stable defect to electronic excitations. The results suggest that the current NIEL model used to estimate the degradation of solar cells has to be revisited.
[1] S.R. Messenger, G.P. Summers, E.A. Burke, R.J. Walters, M.A. Xapsos, Progress in Photovoltaics 9, 103 (2001)
[2] N.E. Koval, F. Da Pieve, E. Artacho, Royal Society Open Science, in press (2020)