Modeling optical properties of thin film Cu(In,Ga)Se2 solar cells using spectroscopic ellipsometry

Abstract

In this research, the optical properties of Cu(In, Ga)Se 2 thin film solar cells were modeled using variable angle spectroscopic ellipsometry and compared against established optical data from bulk materials. Mo, MoSe 2, Cu(In, Ga)Se 2 and US films were measured individually as the devices were formed layer by layer. Optical data, thickness, surface roughness, and the methodology of preparing and effectively modeling samples have been determined. Diffusion of Na from the Soda Lime glass substrate is evident in the optical constants of the Mo layer. The optical constants of the MoSe 2 layer were found to be dependent upon the deposition conditions. The bandgap of the US layer was higher when deposited on Cu(In, Ga)Se 2 surfaces than when deposited on Mo. This implies that greater lattice strain is present in the US layer of solar cell devices than that of US films previously measured in CdS/Mo structures.