Improved interfacial wetability in Cu/ZnO and its role in ZnO/Cu/ZnO sandwiched transparent electrodes

doi:10.1016/j.jmst.2019.06.019

Abstract

Abstract:

Oxide/metal/oxide (OMO) and its derivatives are considered as the promising alternatives to achieve high performance transparent electrodes (TEs). The percolation thickness and conductivity of the metal layer are very crucial for the optoelectrical properties of any OMO TE. Here, we report a facile method to promote the initial growth of the metal layer by improving the interfacial wettability between O-M interface. By subsequently combined with high-quality zinc oxide (ZnO) films, ZnO/Cu/ZnO TEs that have not only low sheet resistance (19.3 Ω/sq) but also enhanced thermal stability can be obtained, with a performance of an average transmittance of 84.4% over the visible spectral range of 400-800 nm.

Key words: Transparent electrodes, Interfacial wettability, UV treatment, Ultra-thin copper film

Mingshi Yu, Guancheng Wang, Rongrong Zhao, Enze Liu, Tonglai Chen. Improved interfacial wetability in Cu/ZnO and its role in ZnO/Cu/ZnO sandwiched transparent electrodes[J]. J. Mater. Sci. Technol., 2020, 37: 123-127.

Figures/Tables 12

Fig. 1. Schematic drawing of the ZnO/Cu/ZnO transparent electrodes (TEs) on a glass substrate (a) and (b) an optical photograph of a transparent electrode based on ZnO/Cu/ZnO.

Fig. 2. XRD patterns of ZnO films with different deposition pressures.

Fig. 3. Dependence of growth rate on the sputtering Ar pressure.

Table 1 Parameters of the ZnO samples estimated from XRD patterns.

Ar pressure (Pa)	FWHM (°)	Lattice constant (nm)	Stress, σ (GPa)
0.7	0.39	0.524	-1.62
1.0	0.64	0.530	-4.23
1.5	0.61	0.526	-2.52
2.0	0.33	0.522	-0.61

Fig. 4. Dependence of the crystallite size on the deposition pressure for ZnO films.

Fig. 5. Optical transmittance as a function of wavelength for ZnO films with different deposition pressures.

Fig. 6. Optoelectrical properties of ultrathin Cu films on ZnO films under different treatment conditions. (a) Change in the sheet resistance of the films as a function of Cu thickness. (b) Average transmittance in the spectral range of 400?-?800?nm versus the sheet resistance for the films.

Fig. 7. Optoelectrical properties of transparent electrodes based on ZnO/Cu/ZnO (a) Change in the transmittance spectra of ZnO/Cu/ZnO TEs with different Cu film thicknesses. (b) The inset is RSδ3 versus δ for determination of percolation threshold.

Table 2 Parameters of the electrode photoelectric performance.

Cu thickness (nm)	Sheet resistance (Ω/sq)	Transmittance(%)	FOM=T¹⁰/R (×10^-3 Ω^-1)
5.1	25.7	84.2	6.97
5.7	19.3	84.4	9.5
6.4	17.0	82.8	8.9

Fig. 8. Change in the contact angle of water on the ZnO film (a) without and (b) with UV treatment.

Fig. 9. Thermal stability for only Cu film and ZnO/Cu/ZnO film, respectively.

Fig. 10. Tape adhesion test of the ZnO/Cu/ZnO film.The inset is a typical picture of tape adhesion test.

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