The development of lightweight and flexible photovoltaic devices is highly desirable for integration in new applications and to reduce the manufacturing cost of modules. In this context, a lot of effort is put into the development of Cu(In,Ga)Se-2 (CIGS) based solar cells on flexible substrates as alternatives to the standard soda-lime glass substrates. Flexible metallic and polyimide foils are frequently used, but in this work we investigated another substrate material presenting advantageous properties: flexible ultra-thin glass. In this article we demonstrated CIGS solar cells with 11.2% efficiency grown on flexible glass as thin as 100 mu m. It was shown that the differences between solar cells fabricated on ultra-thin glass and standard cells fabricated on 1-mm-thick soda-lime glass lie in the lower Na supply in the first case. We also studied the evolution of solar cell performances when they are bent. This last point is rarely discussed in studies on CIGS on flexible substrates in spite of its importance for flexible device applications. (C) 2015 Elsevier B.V. All rights reserved.