1 Local versus global electronic properties of Cu(In,Ga)S2

Thin film solar cells based on Cu(In,Ga)(Se,S)2 have reached record conversion efficiencies well above 20% thus closing the gap to silicon based technologies. The properties of the material can be specifically tuned by adjusting the material composition. For example, Cu(In,Ga)S2 crystallize in the chalcopyrite structure where each Cu, In and Ga cation has four S first nearest neighbors while each S anion is bonded to two Cu and two group-III (In or Ga) atoms. The lattice constants change linearly with In to Ga ratio between those of the ternary end members. Similarly, the band gap o