Light Trapping in Thin-Film Cu(InGa)Se $_{2}$ Solar Cells

A fundamental optical analysis of thin-film Cu(InGa)Se₂ solar cell structures is presented, wherein spectroscopic ellipsometry measurements were performed to acquire material optical constants, which were then used as input parameters to perform electromagnetic simulations. The accuracy of the electromagnetic simulation tools, and thus, the validity of the material optical constants, were verified by comparing the values determined from the simulations with experimental measurements obtained using a spectrophotometer. The verified optical modeling tools were then used to analyze thin, <;0.7-μm Cu(InGa)Se₂ solar cell structures, which do not absorb all incident light within a single optical path length, and hence, the need to incorporate light trapping. To this end, a superstrate device configuration was employed in which the metallic back contact is deposited last, giving rise to an opportunity to incorporate photonic engineering device concepts to the back surface layer of the solar cell. Simulations of superstrate Cu(InGa)Se₂ solar cell designs, complete with light trapping structures were then performed and analyzed.