Improved performance of thin film solar cells based on Cu(In,Ga)S2

Different approaches to the multi-source evaporation of Cu(In,Ga)S-2 for thin film solar cells have been studied. Indirect synthesis via a copper-free precursor film leads to supenor transport properties but also to an inherent grading of the [Ga] /([In] + [Ga]) ratio. Solar cells prepared from these absorbers show confirmed total area conversion efficiencies up to 12.3%, exceeding the previous record for selenium-free chalcopyrite based cells. A more homogeneous gallium depth distribution and a higher absorber band gap have been achieved by modifying the preparation sequence. An efficiency of more than 10% is demonstrated for the first time with high gap chalcopyrite absorbers as required for tandem configurations. (C) 2002 Elsevier Science B.V. All rights reserved.