In this study. optical coatings were investigated as substitutes for the cover-lass on flexible thin-film space solar cells. The inherent low emissivity of copper-indium-gal lium-diselenide (CIGS) thin-film solar cells was increased using optical coatings for thermal balance in space. Evaporated silicon dioxide (SiO2) and an additional aluminum oxide (Al2O3) coating on the CIGS solar cell increased the emissivity from 0.18 to 0.77. Higher emissivity was realized with the Al2O3/SiO2 double-layer coating than with the SiO2 single-layer coating. The straightforward double-layer coating gives the CIGS solar cells appropriate radiative properties for keeping the cell within a permissible temperature range in space. (C) 2007 Elsevier B.V. All rights reserved.