Regulating Ag Wettability via Modulating Surface Stoichiometry of ZnO Substrates for Flexible Electronics

T Lee and D Kim and ME Suk and G Bang and J Choi and JS Bae and JH Yoon and WJ Moon and D Choi, ADVANCED FUNCTIONAL MATERIALS, 31, 2104372 (2021).

DOI: 10.1002/adfm.202104372

A novel and highly efficient methodology to regulate (enhance or suppress) the Volmer-Weber 3D growth mode of ultra-thin (<10 nm) Ag layers by modulating the surface stoichiometry of ZnO substrates prior to Ag deposition is presented. Relative to pristine ZnO layers, oxygen- deficient surface states formed by preferential removal of surface oxygen atoms remarkably improve Ag layer wettability, whereas oxygen- excessive surface states formed by oxygen atom incorporation strongly facilitate Ag agglomeration. The dissimilar nucleation and coalescence dynamics are elucidated via combined molecular dynamics and force-bias Monte Carlo simulations. The improved wettability results in significantly lower sheet resistance in the ultra-thin (6-10 nm) Ag layers, for example, 6.03 omega sq(-1) at 8 nm, than the previously reported values from numerous other approaches in the equal thickness range. When this unique methodology is applied to ZnO/Ag/ZnO transparent electrodes, simultaneous improvement in electrical conductivity and visible transparency is realized, with a resultant Haacke figure of merit value of 0.139 omega(-1) that is >50% higher than the best reported value for an identically structured electrode. We select transparent heating devices as a model system to confirm that the superior optoelectronic properties are highly sustainable under simultaneous and severe electrical, mechanical, and thermal stresses.

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