This work studies hydrogenated amorphous silicon germanium films, deposited by hot wire chemical vapor deposition, to be used as low band gap absorber material in thin film solar cells. Material properties, such as the bonding configurations, the ambipolar diffusion length and the optical band gap, were examined as a function of the substrate temperature and germanium content. Our best materials were incorporated in single junction solar cells with high long-wavelength response and a tandem solar cell with an efficiency of 10.42%. (C) 2015 The Authors. Published by Elsevier B.V.