CIGS solar cells are generally made from Cu-poor absorbers, because their efficiencies have always been higher than those of cells made from absorbers prepared under Cu-excess. However, the electronic quality of absorbers prepared under Cu-excess is better: defect densities are lower, mobilities are higher, bulk recombination is lower. But it has been shown that the interface of absorbers prepared under Cu-excess with the CdS buffer in not-ideal: devices are dominated by interface recombination. Recently we have made progress in preparing absorbers under Cu-excess which have a Cu-poor surface. Building on these results we plan to extend these investigations to make solar cells based on absorbers grown under Cu-excess with efficiencies superior to those prepared from Cu-poor absorbers. The electronic structure of the surfaces and interfaces will be investigated by various opto-electronic methods. The doping level will be controlled by fine tuning of the Cu-excess.