Understanding the selective etching of electrodeposited ZnO nanorods

ZnO nanotubes were prepared by selective dissolution of electrodeposited nanorods. The effect of solution pH, rod morphology, and chloride ion concentration on the dissolution mechanism was studied. The selective etching was rationalized in terms of the surface energy of the different ZnO crystal faces and reactant diffusion. The nanorod diameter and chloride concentration are the most influential parameters on the dissolution mechanism because they control homogeneous dissolution or selective etching of the (110) and (002) surfaces. Bulk solution pH only has an effect on the rate of dissolution. By accurate control of the dissolution process, the nanomorphology can be tailored, and the formation of rods with a thin diameter (10-20 nm), cavity, or ultra-thin-walled tubes (2-5 nm) can be achieved

Control of Photocurrent Generation in Polymer/ZnO Nanorod Solar Cells by Using a Solution-Processed TiO₂ Overlayer

We report herein the fabrication of hybrid conjugated polymer/ZnO photovoltaic devices using ZnO nanorod structures prepared by electrodeposition and study the effect of introducing a second metal oxide overlayer using a TiCl₄ post-treatment. We use transient absorption spectroscopy, scanning electron microscopy, and photovoltaic device measurements to study the microstructure and charge generation properties of the hybrid films and the performance of the resulting devices. We show how the ZnO nanostructure can be controlled via the nanorod growth conditions and demonstrate that photovoltaic device performance can be optimized by controlling the nanostructure in this way. Moreover, we show that a large increase in photocurrent generation can be achieved by coating the ZnO surface with a thin layer of titanium oxide by treating the ZnO nanostructure with a TiCl₄ solution

Electrodeposition of ZnO layers for photovoltaic applications : controlling film thickness and orientation

A systematic study of the effect of the zinc oxide (ZnO) electrodeposition parameters (concentration, temperature, potential and pH) on film morphology, thickness, transparency, roughness and crystallographic orientation is presented with the view of producing optimized thin, planar, and continuous ZnO films for photovoltaic applications. Electrochemical measurements of the deposition charge as a function of time are used to understand the mechanism of nucleation and textured growth. Continuous thin films of crystalline ZnO are obtained at temperatures below 100 degrees C without the need for subsequent annealing. The formation of continuous films is favoured by high concentrations of Zn(2+) precursor (> 100 mM), high temperature (> 70 degrees C) and low potentials (< -1.1 V/AgAgCl). A low bulk solution pH is shown to be a key factor in obtaining thin continuous films and the crystallographic orientation of these films can also be controlled by the deposition parameters. The importance of orientation and thickness control on device performance is shown by using the electrodeposited films as electron extracting interlayers in a model organic photovoltaic system

Electrodeposition of ZnO nanostructures on molecular thin films

Electrodeposition of highly crystalline ZnO nanostructures directly onto copper phthalocyanine and pentacene thin films, from aqueous solutions containing zinc nitrate and dissolved oxygen, has been successfully demonstrated for the first time using a two-step electrochemical deposition process. Importantly, surface activation of the molecular thin film substrates by depositing a thin layer of ZnO nanoparticles at high cathodic overpotentials prior to film growth was found to be crucial for achieving a dense coverage of ZnO nanostructures with uniform morphology. The mechanism for ZnO deposition via electroreduction of hydroxide precursor species (oxygen and NO(3)(-) ions) at the organic-electrolyte interface was shown to be analogous to that reported for conventional inorganic and metal electrodes. Comparison of cathodic current density-time curves, measured during deposition, with film orientation and morphology revealed that the cathodic current density and number of nucleation sites are key factors in determining the characteristics of ZnO film growth on organic substrates. Significantly, the CuPc and pentacene films are not damaged or degraded during this process