Issues on the Chalcopyrite/Defect-Chalcopyrite Junction Model for High-Efficiency Cu(In,Ga)Se2 Solar Cells

Considering the chalcopyrite/defect-chalcopyrite junction model for Cu(In1-xGAx)Se2-based devices and our previously reported findings for the Cu(In1-xGax)3Se5 defect chalcopyrites, we have postulated that univorm high-Ga-content photovoltaic structures (with x > 0.35) do not yield acceptable device performance due to the electrical and structural differences between both types of materials(chalcopyrite and defect-chalcopyrite). In this contribution, the structural properties of the surface region of Ga containing absorber materials have been studies by grazing incidence X-ray diffraction. We find that there are significant differences between surface and bulk. A structural model is proposed for the growth of the chalcopyrite/defect-chalcopyrite junction relative to its Ga content. And we demonstrate thaat closely lattice matched high-Ga-content structures (x > 0.35) can produce solar cells with acceptable performances. The high-voltage and low-current electrical outputs from high Ga structures are very desirable in module fabrication because overall resistive losses can be substantially reduced.