Microstructural properties of Cu(In,Ga)Se2 thin films used in high-efficiency devices

Thin-film polycrystalline photovoltaic devices based on Cu(In,Ga)Se2 have a demonstrated efficiency approaching 19%. The best performance was achieved when the Ga/In+Ga ratio was in the 25–30% range. The short-circuit current density exhibited for the device containing CdS was almost at its expected maximum. The open-circuit voltage was relatively low considering the optical bandgap (Eg) of the above absorber (∼1.15 eV); at best, it is 0.6×Eg. In this work, we examined the microstructural properties, e.g. defects due to misorientation, micro-twinning, stacking faults, and dislocations, for films prepared by our ‘ three-stage’ process, including the CIGS and Mo back-contact. We also attempted to make a correlation between the above observations and device performance.