Abstract
Flexible and crystallized indium–tin oxide (ITO) thin films were successfully obtained on plastic polyethylene terephthalate (PET) films with monolayered graphene as a platform. The highly crystalline ITO (c-ITO) was first fabricated on a rigid substrate of graphene on copper foil and it was subsequently transferred onto a PET substrate by a well-established technique. Despite the plasma damage during ITO deposition, the graphene layer effectively acted as a Cu-diffusion barrier. The c-ITO/graphene/PET electrode with the 60-nm-thick ITO exhibited a reasonable sheet resistance of ~45 Ω sq−1 and a transmittance of ~92% at a wavelength of 550 nm. The c-ITO on the monolayered graphene support showed significant enhancement in flexibility compared with the ITO/PET film without graphene because the atomically controlled monolayered graphene acted as a mechanically robust support. The prepared flexible transparent c-ITO/graphene/PET electrode was applied as the anode in a bulk heterojunction polymer solar cell (PSC) to evaluate its performance, which was comparable with that of the commonly used c-ITO/glass electrode. These results represent important progress in the fabrication of flexible transparent electrodes for future optoelectronics applications.
Highlights
Transparent electrodes are used in various industries, and they are especially popular for application in optoelectronic devices such as flat panel displays, touch sensors, light-emitting diodes (LEDs), and solar cells[1,2,3,4,5,6,7]
The flexible c-indium–tin oxide (ITO)-based transparent-electrode films were first prepared by the growth of single-layered graphene on Cu foils by rapid thermal chemical vapour deposition (RTCVD)[21, 22]
Following the amorphous ITO (a-ITO) deposition, the a-ITO/graphene/Cu films were annealed at 250 °C to obtain the crystalline phase
Summary
The deteriorating transparent-electrode properties with increasing c-ITO thickness might have resulted from the plasma damage to graphene during ITO deposition. The sheet resistance and transmittance of the graphene-supported c-ITO with increasing c-ITO thickness were not as high as those of c-ITO on the glass substrate. The electromechanical durability was evaluated by applying repeated tensile strain to the electrodes composed of graphene-supported c-ITO films with c-ITO thicknesses of 60, 80, 100, and 120 nm This was accomplished by bending the films to radii of curvature of 16, 12, and 8 mm, inducing tensile strains of 0.56, 0.75, and 1.12%, respectively, in the top c-ITO layer. The graphene-supported 60-nm-thick c-ITO film had the best electromechanical stability against bending stress owing to the relatively low plasma damage to the graphene layer. As a step for this research, a whole electrical cell could be fabricated on a copper substrate, and transferred to a transparent substrate by this electrode transferring technique
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