Structure and optoelectronic properties of AZO/Al/AZO tri-layer films grown on flexible substrates

Transparent and conductive AZO/Al/AZO tri-layer films are successfully deposited on flexible poly carbonate (PC) substrates using radio frequency (rf) magnetron sputtering of Al-doped ZnO (AZO) and sputtering with an Al buffer at room temperature. Before the AZO film coating is fabricated, the PC substrates are modified using oxygen plasma etching, to render the surface hydrophilic. The microstructures of these samples are determined using X-ray diffraction (XRD), field emission scanning electron microscopy and transmission electron microscope (TEM). The XRD diffraction patterns and TEM images show that the AZO films are polycrystalline phase with a hexagonal ZnO wurtzite structure. The electrical resistivity, the Hall mobility, the carrier concentration and the optical transmittance of the bi-layer and tri-layer AZO films are strongly dependent on the thickness of the Al buffer layer. When the thickness of the Al buffer is increased, the (002) diffraction peak, shifts slightly to a lower angle and there is a gradual reduction in the value for the full width at half maximum for the AZO films. The microstructure and crystalline characteristics of the bi-layer and tri-layer AZO films are improved by annealing. The figure of merit shows that AZO/Al/AZO tri-layer films wherein the Al is 2 nm thick and which are annealed at 120 °C have better optoelectronic performance.