In view of large-scale exploitation of CuIn1-xGaxSe2 (CIGS) solar cells for photovoltaic energy conversion, it would be quite important not only to increase the conversion efficiency, but also to reduce the thickness of CIGS layer in order to decrease the use of rare and expensive elements, especially Indium. In this work we perform a full study of optical properties of CIGS solar cells grown by a hybrid sputtering/evaporation process, and use the resulting optical functions for electro-optical simulations. We then introduce a texturization of the interfaces and investigate the effects of light trapping on the conversion efficiency. Starting from a CIGS thickness around 2 µm, we show that the same or even higher efficiency can be achieved with much reduced film thickness, with a sizeable effect due to the photonic structure.