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© 2015 Nature Publishing Group. This is the post print version of the following article: Savin, Hele & Repo, Päivikki & von Gastrow, Guillaume & Ortega, Pablo & Calle, Eric & Garín, Moises & Alcubilla, Ramon. 2015. Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiency. Nature Nanotechnology. 11. DOI: 10.1038/nnano.2015.89, which has been published in final form at http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.89.html