Direct Threat of UV–Ozone-Treated Indium-Tin Oxide in Organic Optoelectronics and Stability Enhancement Using Graphene Oxide as Anode Buffer Layer

Ultraviolet (UV)-ozone treatment on indium-tin-oxide (ITO) glass substrates has been widely used in the field of organic optoelectronics for over several decades. ITO glass substrates are currently recognized as standard substrates for highefficiency organic electronics devices. In the first part of this chapter, however, we present evidence for rapid decay of common organic films (e.g., NPB, Alq₃, and rubrene) when they are in direct contact with UV-ozone-treated ITO (UV-ITO) substrates. Photoluminescence (PL), x-ray, and ultraviolet photoemission spectroscopies (XPS, UPS) are used to characterize the reliability of UV-ITO substrates. We conclude that the degradation of organic thin films on UV-ITO substrates are mainly attributed to the active oxygen species generated upon UV-ozone treatments. The oxygen species behave as an oxygen reservoir that interacts with the adsorbed molecules by forming a gap state within its original bandgap and cause charge recombination.
In the second part, we demonstrate the application of a high work function graphene oxide (GO) film as an anode buffer layer for inhibiting those surface-active species on UV-ITO substrates. With the introduction of a GO anode buffer layer, significant enhancements in both the power conversion efficiency (PCE) and stabilities of organic photovoltaic (OPV) devices are observed. This chapter clearly demonstrates the use of a GO buffer layer as a simple and effective approach to improve the performance of OPV devices.