The present invention relates to a thin film solar cell and a method of manufacturing such cells. In particular the invention relates to the use of a composite back contact (314) in Cu(In,Ga)Se2 (CIGS) based thin film solar cells with thin absorber layers. The composite back contact (314) is provided between the substrate (105) and the absorber (115) and comprises: a back reflector layer (311) that enhance the reflectance at the absorber/composite back contact interface; and at least a contact layer that contact layer (310, 313) that ensures suitable electrical properties of the back contact with respect to the absorber; and/or a conductance layer (312) that ensures low sheet resistance for the in-plane current flow.