ZnO nanowire arrays appear as one of the most promising building blocks for photoelectrochemical devices. ZnO can be
efficiently sensitized to solar light absorption by lining its surface with a solar light absorber or by doping with metal
transition impurities. The particular morphology of ZnO nanowires may induce light scattering, increasing solar light
absorption in the sensitizer. The electrodeposition of ZnO nanowire arrays from oxygen reduction was investigated in
this work using Zn2+ precursor salts such as ZnSO4 and Zn(CH3COO)2 instead of the most frequently used ZnCl2.
Important differences in the dimensions of the obtained nanowires were observed. The influence of the adsorbing
behavior of Cl-, SO4- and CH3COO- anions on the growth mechanism was discussed depending of the Zn2+ precursor.
The anion concentration in solution was determined not only by the zinc precursor, but also by the supporting electrolyte
(NaCl, Na2SO4 and CH3COONa) concentrations. By using anions that exhibit different adsorbing properties on the
different ZnO crystalline faces, a new strategy was developed to tailor the dimensions of the ZnO nanowires. The effects
of nanowire length on the light scattering were investigated by optical spectroscopy. An overview of the influence of
these effects on the sensitization of ZnO nanowires to solar light was presented by using ZnO/CdSe core-shell nanowires
as an example.
ZnO nano/microstructures offer the opportunity to design new types of photoelectrochemical devices. Arrays of single crystal ZnO nanowires present very interesting properties to enhance the performance in these devices. A systematic study of the deposition of single crystal ZnO nanowire arrays from the oxygen electroreduction method is reported in order to gain a further insight into the nanowire growth mechanisms and to develop an efficient electrochemical method which allows tailoring the nanowire dimensions. The influence of deposition parameters such as zinc precursor and supporting electrolyte concentrations on the formation of a polycrystalline compact ZnO layer or a ZnO nanowire array, as well as on the dimensions of the single crystal nanowires is analyzed. The effect of the polycrystalline compact ZnO buffer layer on the nanowire nucleation process and therefore on the nanowire diameter and density is also discussed. The results show that electrodeposition is a versatile and cost-effective technique which allows growing ZnO single crystal nanowire arrays with tailored dimensions. The structural and optical properties of electrodeposited nanowire arrays are discussed. ZnO nanowires can be sensitized by the coating of a thin layer of CdSe. The ZnO/CdSe photoanode exhibits excellent photoelectrochemical properties and external quantum efficiency larger than 70 % are observed in ferri/ferrocyanide solutions.
A method was developed for the theoretical calculation of the reflectance for the antireflection coatings made of porous silicon. Although porous silicon has been the focus of interest for the past years, still a satisfactory concept for calculating the reflectance features is lacking. Towards this end, we suggest a new concept that is a combination of the optical matrix method and a graded-bandgap model of porous silicon, which takes into account the gradient in porosity. The calculations based on the optical matrix method were carried out for common antireflection coatings, as well, for MgF2, ZnS and Ta2O5 in order to prove feasibility of the method. A rather good agreement with experimental data was found for all types of antireflection coatings. It is shown that the model of porous silicon as a graded-band semiconductor is valid and is a handy method for the reflectance calculation for porous silicon.
Conference Committee Involvement (11)
Solar Hydrogen and Nanotechnology XI
30 August 2016 | San Diego, California, United States
Solar Hydrogen and Nanotechnology X
9 August 2015 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IX
19 August 2014 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VIII
28 August 2013 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VII
13 August 2012 | San Diego, California, United States
Solar Hydrogen and Nanotechnology VI
23 August 2011 | San Diego, California, United States
Solar Hydrogen and Nanotechnology V
3 August 2010 | San Diego, California, United States
Solar Hydrogen and Nanotechnology IV
3 August 2009 | San Diego, California, United States
Solar Hydrogen and Nanotechnology III
11 August 2008 | San Diego, California, United States
Solar Hydrogen and Nanotechnology II
27 August 2007 | San Diego, California, United States
Solar Hydrogen and Nanotechnology
14 August 2006 | San Diego, California, United States