[220]-oriented Cu(In,Ga)Se/sub 2/-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.