Influence of an additional carbon layer at the back contact–absorber interface in Cu(In,Ga)Se2 thin film solar cells

For paste-coated Cu(In,Ga)Se2 (CIGS) absorber layers used for thin film solar cells one often gets a residual carbon layer between back contact and absorber layer. We investigate the influence of this layer on the solar cells’ performance with co-evaporated CIGS absorbers and find a beneficial effect. The power conversion efficiencies of thin chalcopyrite absorber layers are often limited by the influence of back contact recombination. It is assumed that the carbon layer between the back contact and the absorber layer helps lower this recombination and allows higher open circuit voltages and thus higher conversion efficiencies.