Structural, Optical and Electrical Properties of the Flexible, Asymmetric TiO2/Cu/Ag/ZnS and ZnS/Cu/Ag/TiO2 Films Deposited via Magnetron Sputtering

The structural, optical and electrical properties of the flexible, asymmetric TiO2/Cu/Ag/ZnS and ZnS/Cu/Ag/TiO2 transparent conductive films (TCFs) were studied. The multilayered TCFs were magnetron sputtered onto the flexible PET substrate layer-wise, with TiO2, ZnS, Cu and Ag targets. The atomic force microscope, scanning electronic microscope, X-ray diffractometer, ultraviolet-visible spectrophotometer and four-probe tester were utilized to characterize the samples. The photoelectric property of the multilayers varies with the adjustment in structural parameters. The ZnS/Cu/Ag/TiO2 samples demonstrate a more uniform surface morphology and better optical and electrical properties than the TiO2/Cu/Ag/ZnS counterparts. The optimal sheet resistance and average transmittance of the ZnS/Cu/Ag/TiO2 films are 5.56 Ω/sq and 88.46% in the visible spectrum, with the corresponding figure of merit reaching 52.76 × 10−3 Ω−1. The bottom ZnS layer reveals superior percolation function for the bimetallic layer, forming with good continuity and homogeneity, although the original surface roughness is higher than that of TiO2. The top TiO2 layer demonstrates a smooth morphology and dense structure, beneficial to the high transparency and stability of the multilayer.