Recycling Indium Tin Oxide (ITO) Electrodes Used in Thin-Film Devices with Adjacent Hole-Transport Layers of Metal Oxides

Many thin-film optoelectronic devices use electrodes made of tin-doped indium oxide (ITO), which is acceptably conductive, as well as virtually transparent and colorless. Regrettably, indium is an uncommon element and its price continues to rise, so it is increasingly important to recover ITO electrodes from devices that are no longer needed. Previous work has shown that simple sonication in neutral water can separate intact ITO electrodes from other components in typical devices, in which the active components and ITO are separated by an ionic buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Sonication in water appears to be effective because it favors selective penetration and dissolution of PEDOT:PSS, thereby freeing the underlying ITO electrode. However, PEDOT:PSS is being replaced in emerging devices by the use of various metal oxides as hole-transport materials. We have now found that ITO electrodes in these new devices can be recycled by sonication in dilute aqueous base. The layers of ITO undergo only minor changes in composition and morphology, and the recovered electrodes can be reused many times to fabricate new devices without loss of performance.