(220)-oriented Cu(In,Ga)Se2-evidence that it may improve solar cell performance

Recent solar cell results suggest that a (220) or (204) orientation of CIGS thin films may have unique and possibly superior properties. The authors have deposited high-quality epitaxial mixed (220) and (204)-oriented CIGS layers on GaAs (110). The surfaces consist of highly tilted terraces of large flat (112) facets alternating with rough (112) planes. Temperature-dependent Hall-effect shows up to a 20 fold decrease in carrier concentration relative to films grown with (112) and (002) orientations. Carrier compensation and other defects observed in the (002) and (112) oriented films was reduced without Na addition in the (220)/(204) films. Changes in the hole mobility were also observed. Theoretical modeling using the AMPS computer code suggests that such a change in carrier concentration could lead to improvements in device performances in sufficiently good devices, consistent with observations