Theoretical study on the effect of an intermediate layer in CIS-based ETA-solar cells

Abstract

A theoretical treatment is given of the mechanisms that might be responsible for reported improvements in solar cell characteristics of, in particular, TiO 2/CuInS 2 based nanostructured ETA-solar cells. Especially, the possible benefits of the insertion of an intermediate tunnel barrier (Al 2O 3, MgO) or buffer layer (CdS) are investigated. Three mechanisms to improve V oc without compromising J sc are discussed: (i) introduction of an energy barrier which is higher for dark current than for light current; (ii) reduction of the interface state density at either side of the intermediate layer (IL) compared to the structure without IL, for materials reasons; and (iii) reduction of the effect of interface states due to a more favourable position of the Fermi levels at the interface, with respect to the band edges. The dark saturation current and hence V oc turn out to be determined by interface recombination, and chemical and electrostatic interactions at the interfaces.