Etch-Resistant Zn1-xMgxO Alloys: An Alternative to ZnO for Carboxylic Acid Surface Modification: An alternative to ZnO for carboxylic acid surface modification

Zinc oxide (ZnO) is a high bandgap transparent metal oxide used extensively in organic electronic devices and dye-sensitized solar cells (DSSCs) as an electron accepting and transporting material. Carboxylic and other organic acid attachment schemes are often employed to sensitize or functionalize the surface of ZnO in these applications. Unfortunately, one weakness of ZnO is its high susceptibility to etching by even weak acids. This has a substantial negative impact on ZnO DSSCs which use carboxylic acid groups to attach dyes to ZnO and also influences attachment techniques for functionalizing ZnO in organic electronic devices. By substituting Mg for Zn atoms to form Zn _1-xMg_xO (ZnMgO) alloys, a material with similar electronic properties but higher etch resistance is achieved. Here, we show that the etch rate of Zn_0.8Mg_0.2O, when exposed to the prototypical modifier benzoic acid (BA), is an order of magnitude lower than that of ZnO. Infrared spectroscopic characterization of BA-modified ZnMgO indicates that BA binds to the surface in two different conformations, the relative proportion of which changes with Mg content. The IR spectra also provide evidence of the presence of physisorbed zinc benzoate complexes that are likely a product of etching, as their presence increases with exposure time. Possibilities for the mechanism of improved etch resistance are discussed via the literature on metal oxide dissolution.