Elucidation of homojunction formation in CuInS2 with impedance spectroscopy

Type transformation in CuInSe2 and CuInS2 solar cells is an important issue with far reaching consequences. In the present study, the presence of a p-n homojunction inside CuInS2 in a TiO2/CuInS2 device is revealed with a detailed impedance spectroscopy and capacitance study. A n-type CuInS2 film with a thickness of 40?nm is found at the TiO2 (n-type)/CuInS2 (p-type) interface. The effective donor density of this n-type film is 2×1017?cm?3 at 400?K and is higher than the effective acceptor density in the remaining p-type CuInS2, being 4×1016?cm?3 at 400?K. Both densities decrease upon increasing the temperature. This is explained by the activation of a CuIn? acceptor state in n-type CuInS2 and a thermally activated hole trap in p-type CuInS2