Characteristics of Flexible ITO Electrodes Grown by Continuous Facing Target Roll-to-Roll Sputtering for Flexible Organic Solar Cells

Abstract

The preparation and characteristics of flexible indium tin oxide (ITO) electrodes grown on polyethylene terephthalate (PET) substrates are described for use in flexible organic solar cells and prepared using a specially designed facing target roll-to-roll sputtering (FTRS) system. Due to the effective confinement of the high-density plasma between two facing ITO targets, we can deposit the ITO electrode continuously on the PET substrate at a substrate temperature below 50°C without the need of a substrate cooling system, which is used in conventional roll-to-roll sputtering systems. In spite of a low substrate temperature, the FTRS-grown flexible ITO electrode showed a sheet resistance of 42.2 Ω/square, a resistivity of 8.44 × 10 -4 Ω cm, and a transmittance of 85.41% in the 500-550 nm wavelength range with superior flexibility. Furthermore, the flexible organic solar cell fabricated on the FTRS-grown flexible ITO electrode at optimized conditions exhibited a power-conversion efficiency of 2.43%, which is similar to an organic solar cell fabricated on a reference dc sputter-grown ITO electrode. This indicates that the FTRS technique is a promising continuous-sputtering process for preparing flexible ITO electrodes and can substitute for conventional roll-to-roll sputtering systems for mass production of flexible solar cells.