TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The contact layer modifies the electrical properties of composite back contact with respect to the property or properties of composite back contact with respect to contact resistance for majority carriers, and/or back contact recombination of minority carriers.The absorber is thin film of p-type semiconductor copper (indium, gallium) selenide, copper, (indium, gallium) selenide (CIGS), or copper (indium, gallium) (selenide, sulfide), or copper (aluminum, indium) (selenide, sulfide). The composite back contact comprises conductance layer between the reflector layer and substrate. The conductance layer lowers the sheet resistance of solar cell. The composite back contact layer comprises contact layer provided between the reflector layer and absorber. The contact layer provides low series resistance for majority holes and/or low back contact recombinant for minority electrons.The reflector layer is made by material giving reflectance at the absorber/composite back contact interface greater than 0.5 in region of photon energy of 0-0.2 eV on the optical bandgap of the absorber. The reflector layer is made of transition metal nitride(s), e.g. zirconium nitride, hafnium nitride, or titanium nitride. The reflector layer can also be formed of element metal(s), e.g. silver, aluminum, or gold. The conductance layer is made by material giving sheet resistance for in-plane current flow less than 2Omega/square.The conductance layer is made of molybdenum. The contact layer is formed by semi-conductor material of the same conductivity type as the absorber. The contact layer provides total contact resistance of absorber and back contact less than 1 Omegacm2. The contact layer is made of selenide or sulfide of metallic element. The metallic element is Group IVB, e.g. titanium, zirconium, hafnium; Group VB, e.g. vanadium, niobium, tantalum; Group VIB, e.g. chromium, molybdenum, tungsten; or Group VIIB, e.g. manganese, rhenium in the periodical system.The contact layer is preferably made of molybdenum selenide. The contact layer is made of the same chalcopyrite material class used in the absorber. The contact layer is made of the same chalcopyrite material class as used in the absorber but has higher majority carrier concentration. The contact layer is made of the same material class as used in the absorber but with the atomic composition changed to obtain higher bandgap compared to the average bandgap in the absorber. The contact layer is composite contact layer containing contact layers. The composite contact layer is made of copper indium gallium (selenide, sulfide) and molybdenum selenide.x = greater than average value of x in the absorberThe composite back contact is realized with single material, preferably zirconium nitride. The reflector layer is resistant to corrosion, thus protecting the composite back contact from corrosion.Preferred Methods: The forming of contact layer comprises providing first and second contact layers. The first contact layer is made by semi-conductor material of the same conductivity type as the absorber. The second contact layer is formed by the same material class as used in the absorber but with higher bandgap and/or majority carrier concentration.