Abstract
Copper is coated on indium-tin-oxide (ITO) thin film to improve its electrical resistivity. In order to recycle the scrap Cu/ITO thin film, an ionic liquid (1-butyl-3-methyl imidazolium hexafluorophosphate ([C4mim][PF6])) containing iodine/iodide (IL-I) was used to extract copper at 303, 343, 413, 374, and 543 K. The extraction efficiency of copper from the scrap Cu/ITO thin film was >99% with IL-I. Using XRD, crystal In2O3 was found on the regenerated ITO thin film which had a resistivity similar to that of unused ITO thin film. Using X-ray absorption near edge structural (XANES) spectroscopy, at least two paths for the extraction of copper from the Cu/ITO thin film into IL-I were identified. Path I: Copper is stripped from the scrap Cu/ITO thin film and then interacts with I3− in the IL-I to form nano CuI. The nano CuI further interacts with I−. Path II: Copper interacts with I3− on the surface of the Cu/ITO thin film to form nano CuI. The nano CuI is further stripped into the IL-I to interact with I−. During extraction, the nanoparticle size could be increased in the IL-I by conglomeration due to fewer coordinating anions and decrease in the viscosity of IL-I at high temperatures. Furthermore, nanoparticle growth was affected by [PF6]− of the IL-I determined via 31P NMR.
Highlights
The electrical resistivity and band gap of Cu/ITO thin film are decreased by doping copper nanoparticles, which can be applied onto flexible optoelectronic devices with high substrate temperatures, etc
About 99% of the copper on the surface of the scrap Cu/ITO thin film was extracted into the IL-I at 303–543 K within 30 min
The crystal In2O3 was still maintained on the regenerated ITO thin film
Summary
Indium-tin-oxide (ITO) thin film is composed of In2O3 and SnO2 and applied on transparent electrodes for touch screens, EMI shielding, storage devices, and photovoltaic solar cells [1–4]. In order to improve the optoelectrical properties and appropriable optical band gaps, the copper is doped onto the ITO thin film [5,6]. The electrical resistivity and band gap of Cu/ITO thin film are decreased by doping copper nanoparticles, which can be applied onto flexible optoelectronic devices with high substrate temperatures, etc. Demand for ITO thin film has increased as usage and applications have increased. The prices of indium and tin will continue to increase due to increase in demand. Dilute aqueous base or acid is used to dissolve indium and tin from ITO thin film and the metals are separated from the solutions [10]. Appropriate technologies should be developed to recycle intact ITO thin film
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