Surface Structure Modification of ZnO and the Impact on Electronic Properties

Abstract

Zinc oxide (ZnO) is a widely utilized, versatile material implemented in a diverse range of technological applications, particularly in optoelectronic devices where its inherent transparency, tunable electronic properties, and accessible nanostructures can be combined to confer superior device properties. ZnO is a complex material with a rich and intricate defect chemistry, and its properties can be extremely sensitive to processing methods and conditions; consequently, surface modification of ZnO using both inorganic and organic species has been explored to control and regulate its surface properties, particularly at heterointerfaces in electronic devices. Here, we describe in detail the properties of ZnO, particularly its surface chemistry and the role of defects in governing its electronic properties, and describe methods employed to modulate the behavior of asgrown ZnO and outline how the native and modified oxide interact with molecular materials. To illustrate the diverse range of surface modification methods and their subsequent influence on electronic properties, a comprehensive review of modification of ZnO surfaces at molecular interfaces in hybrid photovoltaic (hPV) and organic photovoltaic (OPV) devices is presented. This is a case study rather than a progress report, aiming to highlight the progress made towards controlling and altering the surface properties of ZnO, and to bring attention to the ways in which this may be achieved by using various interfacial modifiers (IMs).2

Controlled Defects of Fluorine-incorporated ZnO Nanorods for Photovoltaic Enhancement

“…In the field of organic photovoltaics, a great research endeavor has been committed to replace fullerene with transparent metal-oxides (TMO) as electron acceptor in bilayer hybrid solar cells (HSC), in order to overcome the uncontrollable phase separation, fabrication complexity and air-stability issue of fullerene based device12. Solution-processed ZnO nanorods (ZNR), in particular, has been the most prominent TMO based inorganic electron acceptor latterly owing to its flexible synthesis route, high electron affinity and tunable morphology including size, diameter, density and rod-to-rod spacing to yield high surface-to-volume ratio34. In addition, the high hydrophobicity and vertical alignment of ZNR could facilitate the infiltration of polymer, thus providing a large donor-acceptor interfacial area and direct electron conduction pathway in vertically-stacked device35.…”

Improved Stability of Polymer Solar Cells in Ambient Air via Atomic Layer Deposition of Ultrathin Dielectric Layers

“…[8][9][10] Among solution-processed interfacial materials, metal oxides with intrinsic n-type conductivity, such as zinc oxide (ZnO), have been considered as promising candidates for EELs due to their inherent transparency, tunable electronic properties, low toxicity, and facile thin-film preparation through a diverse range of solution-processing techniques. [11][12][13][14][15] However, surface defects of ZnO that act as electron-trapping sites, and moisture and oxygen species adsorbed therein, that have been proven to be corrosive agents, strongly degrade solar cell performance and have a negative impact on the cell stability. [16][17][18][19][20][21] Therefore, the development of processes for effective passivation of surface defects of ZnO is of vital importance in order to enhance the device stability.…”

Veritable electronic characteristics in ZnO nanowire circuits uncovered by the four-terminal method at a low temperature

“…[4][5][6] Most of the prototypes designed on individual semiconductor nanowires are demonstrated with a two-terminal configuration, in which a semiconductor nanowire is contacted with two conducting electrodes and the current can flow through the non-superconducting nanowire because of the superconducting proximity effect. [7][8][9] One well-known problem associated with such devices is that the source/drain contact resistance becomes an important parameter limiting the charge carrier transport and device performance with decreasing channel width in the nanoscale systems. For example, the electronic characteristics of the contact strongly depend on the metal work function and electron affinity.…”