The epitaxial lift-off technique can be used to separate a III-V solar cell structure from its underlying GaAs substrate. Processing a thin-film cell is somewhat different from a regular cell on substrate, In this work a number of critical issues, e.g., a low-temperature anneal front contact and the metal mirror on backside of the thin-film are optimized. Together with an improved active layer material quality, grid mask and anti-reflection coating this leads to thin-film cells as good as cells on a substrate, with record efficiencies for single junction GaAs solar cells of 26.1% for both cell types. (C) 2009 Elsevier B.V. All rights reserved.