Band gap engineering in polycrystalline Cu(In,Ga)(Se,S)2 chalcopyrite thin films

The reaction of metallic alloys to selenium and/or sulfur is a promising two-step growth process to produce chalcopyrite absorber films for application in thin film photovoltaic devices. However, the success of these classical two-step growth processes is limited by insufficient control over the lattice parameters and the band gap of the compound semiconductor films. This problem, which is perceived to be insurmountable, is directly related to the poor control over the diffusion properties of gallium and sulfur in the thin films under typical growth conditions. In this contribution, it is indicated for the first time that single-phase Cu(In1-xGax)(Se1-ySy)2 pentenary alloys can be produced by the selenization/sulfurization of copper–indium–gallium metallic alloys. Even more significantly, it will be demonstrated that the reaction parameters (i.e. gas concentrations, reaction temperature, and time) during the selenization process can be manipulated to control the lattice parameters and band gap values of the pentenary semiconductor alloys.