Poly (ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) has a smooth surface that can be modified by addition of metal oxides. The smooth surface which can be altered to have "hill like" structures by addition of NiOx doping in the PEDOT:PSS indicates the formation of insulating film of PSS. Such PSS insulating layer may have similar advantages to the LiF insulating barrier used in organic electronics. The addition of NiOx crystallites, produced insulating films of PSS of thickness varying from 3.35 to 7.17 nm. The production of these layers could be the explanation for the excellent stability of inverted OPVs with a PEDOT:PSS:NiOx interlayer as used in our study. (C) 2014 Elsevier B.V. All rights reserved.