Although the defects introduced by irradiation in Si and GaAs have been extensively studied, the centres giving rise to non-radiative recombination have been neither characterized nor identified. We propose here a method allowing one to fully characterize recombination centres, i.e. to obtain their electron and hole capture cross sections as well as their concentration. It is based on a correlation between data extracted from the current-voltage characteristics of a junction in dark, deep level transient spectroscopy and the variations of the short-circuit current and open voltage of solar cells versus the logarithm of the irradiation fluence. The method is applied to characterize and tentatively identify the recombination centres introduced by electron irradiation in Si, GaAs and InGaP.

We demonstrate a simple self-assembly method based on solid state dewetting of ultra-thin silicon films and germanium deposition for the fabrication of efficient anti reflection coatings on silicon for light trapping. Via solid state dewetting of ultra-thin silicon on insulator and epitaxial deposition of Ge we fabricate SiGe islands with a high surface density, randomly positioned and broadly varied in size. This allows to reduce the reflectance to low values in a broad spectral range (from 500 nm to 2500 nm) and a broad angle (up to 55 degrees) and to trap within the wafer a large portion of the impinging light (∼40%) also below the band-gap, where the Si substrate is non-absorbing. Theoretical simulations agree with the experimental results showing that the efficient light coupling into the substrate mediated by Mie resonances formed within the SiGe islands. This lithography-free method can be implemented on arbitrarily thick or thin SiO2 layers and its duration only depends on the sample thickness and on the annealing temperature.

We propose the use of electroluminescence to measure irradiation-induced degradation of multijunction photovoltaic cells in order to probe the degradation of each individual junction. We illustrate the technique by studying the decrease of the luminescence of GaInP, GaAs and Ge junctions of a triple-junction solar cell produced by 1 MeV electrons for fluences corresponding to space conditions.

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