Role of residual stress and texture of ZnO nanocrystals on electro-optical properties of ZnO/Ag/ZnO multilayer transparent conductors

Abstract

A broad study on transparent and conducting ZnO/Ag/ZnO multilayer thin films is presented in this report. Bottom ZnO layer, mid Ag layer, and top ZnO layer are deposited on flexible and glass substrates by Pulsed DC and DC magnetron sputtering technique. X-ray diffraction (XRD) studies of multilayer structures reveal formation of nanocrystalline wurtzite ZnO which exhibit (002) preferable orientation along with the feeble appearance of (111) peak of Ag from the intermediate layer. High transmittance of 81.8% with low sheet resistance 17.0 Ω/sq are achieved for ZnO/Ag/ZnO thin films deposited on glass and transmittance of 77.3% with sheet resistance 14.7 Ω/sq are observed for ZnO/Ag/ZnO thin films deposited on PET. XRD studies facilitate to understand the role of texture and residual stress of ZnO on the electro-optical properties of ZnO/Ag/ZnO multilayer thin films. XRD analyses and electro-optical measurements confirm that the tensile residual stress of ZnO above certain level is favourable for lower sheet resistance primarily due to the lattice extension in the transverse direction to the film surface. Due to high Hall mobility, low sheet resistance and reasonably good figure of merit, sputtered ZnO/Ag/ZnO multilayer thin films meet the requirements of transparent conductors in photovoltaics.