NOVELTY - A thin film solar cell comprises substrate, absorber, and composite back contact. The composite back contact is provided between substrate and absorber. The composite back contact comprises back reflector layer, and contact layer and/or conductance layer. The back reflector enhances the reflectance at the absorber/composite back contact interface. The contact layer ensures electrical properties of back contact with respect to the absorber.    USE - Used in providing electrical power.    ADVANTAGE - The assembly has contact layer that ensures electrical properties of the back contact with respect to the absorber and conductance layer ensuring low sheet resistance for in-plane current flow. IT protects the other layers of composite back contact from corrosion and exposure to high temperature and aggressive chemical environment during growth of CIGS absorber.    DETAILED DESCRIPTION - A thin film solar cell comprises substrate (105), absorber (115), and composite back contact (314). The composite back contact is provided between the substrate and absorber. The composite back contact comprises back reflector layer (311), and contact layer (310, 320) and/or conductance layer (312). The back reflector enhances the reflectance at the absorber/composite back contact interface. The contact layer ensures electrical properties of back contact with respect to the absorber. The conductance layer ensures low sheet resistance for in plane current flow.    An INDEPENDENT CLAIM is included for manufacturing thin film solar cell comprising providing substrate and absorber, forming the back reflector layer close to the absorber, forming conductance layer on substrate, and/or forming contact layer between the reflector layer and absorber, thus providing the composite back contact between the substrate and absorber.    DESCRIPTION OF DRAWING(S) - The figure shows a device structure.    Substrate (105)    Absorber (115)    Contact layer (310, 320)    Back reflector layer (311)    Conductance layer (312)    Back contact (314)