Defect chalcopyrite Cu(In1-xGax)3Se5 materials and high Ga-content Cu(In,Ga)Se2-based solar cells

Crystallographic, optical, and electrical properties of defect chalcopyrite Cu(In_1-xGa)₃Se₅ (0<x<1) materials in polycrystalline thin-film form are reported. Also, an energy band alignment between such materials and CdS has been calculated from X-ray photoelectron spectroscopy data. A comparison of some properties against published data on similarly prepared chalcopyrite CuIn_1-xGa_xSe₂ absorber materials is presented. Considering the chalcopyrite/defect chalcopyrite junction model, we postulate that the traditionally poor device performance of uniform high-Ga-content absorbers (x>0.3) is due to a relatively inferior character-both structural and electrical-at the very chalcopyrite/defect chalcopyrite interface. We demonstrate that this situation can be circumvented (for absorbers with x>0.3) by properly engineering such an interface by reducing Ga content in the region near the surface of the absorber