Superstrate CdTe-based thin-film solar cells with conversion efficiencies higher than 15% have been synthesized on commercial SnO2:F/SnO2-coated soda-lime glass substrates without anti-reflection coating. The n-type CdS window layers were prepared by R. F. sputtering in an ambient containing a small amount of oxygen concentration. CdTe absorber layers were obtained by close-spaced sublimation (CSS). The post deposition CdCl2 activation was conducted in a dry air ambient. With the application of elemental Cu/Au back contacts, the best small-area CdTe cells (0.08 cm(2)) have shown an efficiency of 15.5% with an open-circuit voltage of 844 mV, a short-circuit current of 24.0 mA/cm(2), and a fill-factor of 76.6% measured under an AM1.5 illumination. This efficiency was achieved when a 1% O-2 concentration was used in sputtering ambient during CdS deposition. (C) 2013 Elsevier B. V. All rights reserved.