Interfacial Chemistry with ZnO: In Operando Work Functions in Heterocells

Abstract

Interfacial additives such as oxides may help solve diffusion and nucleation obstacles in heterojunctions of solid-state devices. Healing strategies may rely on them, particularly in ZnO, which has numerous applications, from photovoltaics and sensors to superconductors and batteries as a lithiumphilic interlayer. Here, we show a case study based on in operando cells with two heterojunctions and the ZnO as a dielectric semiconductor. The cells show how the Cu/ZnO surface chemical potentials equalize by forming a more negatively charged region where nucleation of a new phase will likely be facilitated and the dielectric's role in interlaying with negative and positive electrodes. The highly ohmic behavior of the interface, negative electrode (metal)/dielectric, is also analyzed. The advantage of the scanning Kelvin probe (SKP) in studying the surface chemical potentials is demonstrated. Ab initio simulations used density functional theory (DFT) and hybrid functional HS06 to determine the bulk ZnO's band structure and optical properties, including relative permittivities. Aluminum, zinc, copper, and zinc oxide work functions were obtained after simulating the correspondent surfaces and compared with contact potentials obtained with SKP. The study extends hyperbolically into the cell's dimensions to understand all of the interplays of the components. An unexpected long-range equalization of the surface chemical potentials of the three cell constituents away from the interfaces may mirror a metal-insulator-metal plasmonic interaction that can be tailored for solar applications.