In this study, the effects of (NH4)(2)S-x treatment on the electrical and optical properties of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) electrodes were researched. The authors found that (NH4)(2)S-x treatment could result in suppressing the hysteresis-type current-voltage characteristics related to the interfacial capacitance variation and a reduction in the equivalent refractive index of the ITO/PEDOT:PSS electrodes, owing to the improvement in the interfacial stability of the ITO/PEDOT: PSS electrodes and a reduction in the interface trap-states related charge store at the ITO/PEDOT:PSS interface. This implies that the ITO/PEDOT:PSS electrodes fabricated using the (NH4)(2)S-x-treated ITO may produce a higher extraction efficiency for ITO/PEDOT:PSS-based optoelectronic devices. (C) 2009 Elsevier B.V. All rights reserved.