Study of the surface properties of ZnO nanocolumns used for thin-film solar cells

Densely packed ZnO nanocolumns (NCs), perpendicularly oriented to the fused-silica substrates were directly grown under hydrothermal conditions at 90 °C, with a growth rate of around 0.2 μm/h. The morphology of the nanostructures was visualized and analyzed by scanning electron microscopy (SEM). The surface properties of ZnO NCs and the binding state of present elements were investigated before and after different plasma treatments, typically used in plasma-enhanced CVD solar cell deposition processes, by X-ray photoelectron spectroscopy (XPS). Photothermal deflection spectroscopy (PDS) was used to investigate the optical and photoelectrical characteristics of the ZnO NCs, and the changes induced to the absorptance by the plasma treatments. A strong impact of hydrogen plasma treatment on the free-carrier and defect absorption of ZnO NCs has been directly detected in the PDS spectra. Although oxygen plasma treatment was proven to be more efficient in the surface activation of the ZnO NC, the PDS analysis showed that the plasma treatment left the optical and photoelectrical features of the ZnO NCs intact. Thus, it was proven that the selected oxygen plasma treatment can be of great benefit for the development of thin film solar cells based on ZnO NCs

Three-dimensional amorphous silicon solar cells on periodically ordered ZnO nanocolumns

We evaluate the potential of three-dimensional (3D) thin-film silicon solar cells in the superstrate configuration deposited on hexagonally ordered arrays of ZnO nanocolumns (NCs). These nanostructures are prepared by hydrothermal growth, which is an effective and versatile method to obtain ZnO NCs of high optical and electrical quality at low temperature. For the periods P investigated, varied between 0.9 and 1.4m, 3D solar cells based on hydrogenated amorphous silicon (a-Si:H) exhibit a photocurrent (J(SC)) boost in the red wavelength range as compared to flat cells; this J(SC) gain (by more than 1.5mAcm(-2) for P=0.9m) is explained mostly by the increased effective optical thickness of the absorber layer grown on the vertical walls of the NCs. Combining this 3D concept with randomly textured interfaces, rigorous 3D optical simulations based on the finite element method predict that photocurrents significantly higher than those obtained with state-of-the-art substrates (up to 20mAcm(-2)) are within reach, if the experimental obstacles specific for 3D design are overcome

Nanocrystalline Boron-Doped Diamond as a Corrosion-Resistant Anode for Water Oxidation via Si Photoelectrodes

Due to its high sensitivity to corrosion, the use of Si in direct photoelectrochemical (PEC) water-splitting systems that convert solar energy into chemical fuels has been greatly limited. Therefore, the development of low-cost materials resistant to corrosion under oxidizing conditions is an important goal toward a suitable protection of otherwise unstable semiconductors used in PEC cells. Here, we report on the development of a protective coating based on thin and electrically conductive nanocrystalline boron-doped diamond (BDD) layers. We found that BDD layers protect the underlying Si photoelectrodes over a wide pH range (1-14) in aqueous electrolyte solutions. A BDD layer maintains an efficient charge carrier transfer from the underlying silicon to the electrolyte solution. SiIBDD photo electrodes show no sign of performance degradation after a continuous PEC treatment in neutral, acidic, and basic electrolytes. The deposition of a cobalt phosphate (CoPi) oxygen evolution catalyst onto the BDD layer significantly reduces the overpotential for water oxidation, demonstrating the ability of BDD layers to substitute the transparent conductive oxide coatings, such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO), frequently used as protective layers in Si photoelectrodes