Enhancement of electrical properties of flexible ITO/PET by atmospheric pressure roll-to-roll plasma

Flexible materials can significantly reduce the cost of the electronic devices because they can be manufactured by large-area roll-to-roll (R2R) processing. In this work, R2R atmospheric pressure plasma was used to modify flexible indium-tin-oxide films on polyethylene terephthalate foil (ITO/PET). Plasma treatment was performed in different feed gases consisting of various ratio between nitrogen and oxygen. A range of experimental techniques were used to study surface properties of ITO/PET, including X-ray and Ultraviolet photoelectron spectroscopies, four-point probe, Atomic force microscopy and UV-Vis measurement. We found that R2R plasma treatment decreased carbon contamination and increased the number of oxygen vacancies on the surface, whereas the ratio between indium and tin remained constant. UPS showed an increase in the work function from 3.9 eV for untreated sample to 5.1 eV for sample treated in plasma for very short time of 2 s. Four-point probe measurement demonstrated remarkable decrease in sheet resistance from 44.2 Omega/sq to 11.7 Omega/sq after plasma treatment for 2 s. The AFM and UV-Vis measurements revealed only slightly change on the surface morphology and transmittance of the ITO/PET. The plasma treated foils were stored under laboratory environment and inside of the glovebox to study the effect of the environmental conditions on the stability of the improved properties. The ITO surfaces stored in laboratory environment for 3 weeks preserved approx. 60% of the properties achieved by plasma treatment, e.g. work function of the samples was approx. 4.5 eV after 3 weeks (and 5 weeks) ageing time in the laboratory environment.