Experimental verification of optically optimized CuGaSe2 top cell for improving chalcopyrite tandemsM. Schmid, R. Caballero, R. Klenk, J. Krč, T. Rissom, M. Topič and M. Ch. Lux-SteinerEPJ Photovolt., 1 (2010) 10601DOI: https://doi.org/10.1051/epjpv/2010002