Improved broadband antireflection in Schottky-like junction of conformal Al-doped ZnO layer on chemically textured Si surfaces
TL;DR: In this paper, chemically textured Si with improved absorption in the complete range of solar spectrum was investigated by ultraviolet/visible/near-infrared (UV/Vis/NIR) spectroscopy, showing an average specular reflectance of ∼ 0.4% in the wavelength of 500-3000nm.
Abstract: Chemically textured Si with improved absorption in the complete range of solar spectrum is investigated by ultraviolet/visible/near-infrared (UV/Vis/NIR) spectroscopy, showing an average specular reflectance of ∼0.4% in the wavelength of 500–3000 nm. The pyramidal structures on such solar-blind Si can reduce the reflectance further below 0.1% in the UV region by conformal growth of granular Al-doped ZnO (AZO) films. X-ray diffraction analyses suggest the growth of polycrystalline AZO on faceted-Si. Moreover, marginal increase in electrical conductivity of AZO is found on textured surfaces, whereas rise in leakage current in Schottky-like Ag/AZO/Si/Ag heterostructure devices is noticed with increasing Si surface area.
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TL;DR: In this article, the authors investigate the broad-band photoabsorption of an n-TiO2 thin film and its hole-blocking properties when a heterostructure is grown on a chemically textured p-Si substrate.
43 citations
TL;DR: In this article, temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV Ar+ ions.
Abstract: Temperature-dependent photoluminescence (PL) of titanium oxide (TiO2) shows an evolution of blue emission when exposed to 50 keV Ar+ ions. The origin of observed PL has been examined by X-ray absorption near-edge spectroscopy (XANES) at Ti-K,L and O-K edges, revealing the reduction of ligand field splitting owing to the formation of oxygen vacancies (OVs) by destroying TiO6 octahedral symmetry. Detailed PL and XANES analyses suggest that the fluence (ions/cm2) dependent increase in OVs not only boosts the conduction electrons but also increases the density of holes in localized self-trapped exciton (STE) states near the valence band. Based on these observations, we propose a model in which doped conduction electrons are recombining radiatively with the holes in STE states for blue light emission.
37 citations
TL;DR: In this article, the effect of the thickness of the TiO2 thin film on the structural, optical, electrical and photovoltaic properties has been investigated using the well-known thermal evaporation technique.
32 citations
TL;DR: In this article, the authors investigated the hydrophobicity of self-assembled TiO2 nanorods on chemically etched Si pyramids by irradiating with 50 keV Ar+-ions at room temperature.
Abstract: Oxygen vacancy (OV) controlled hydrophobicity of self-assembled TiO2 nanorods (NRs) on chemically etched Si pyramids is investigated by irradiating with 50 keV Ar+-ions at room temperature. Apparent contact angle (CA) is found to increase from 122° to 141° up to a fluence of 1 × 1015 ions/cm2, followed by a gradual reduction to 130° at 1 × 1017 ions/cm2. However, the drop in apparent CA is found to be associated with the decrease in fractional surface area via transformation of NRs to an amorphous layer above 1 × 1015 ions/cm2, though it is still higher than that of as-grown one. Detailed X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements suggest that the control of hydrophobic behavior is related to the suppression of surface free energy via migration of OVs into the voids in TiOx layers.
23 citations
TL;DR: In this article, the authors investigated the optical-bandgap (Eg) of self-assembled crystalline TiO2 nanorods to amorphous layer and the corresponding impact on Si pyramids by irradiating with 50'keV Ar+-ions.
Abstract: Transformation of self-assembled crystalline TiO2 nanorods to amorphous layer, and the corresponding impact on optical-bandgap (Eg) on Si pyramids are investigated by irradiating with 50 keV Ar+-ions. Initially, Eg is found to be reduced from 3.23 to 2.94 eV up to a fluence of 1 × 1016 ions/cm2, and discussed in terms of the rise in oxygen vacancies (VO). However, a sudden increase in Eg to 3.38 eV is detected at a fluence of 1 × 1017 ions/cm2 through evolution of voids by over-saturating VO, manifesting the appearance of degenerate states by shifting the Fermi level above the conduction band minimum via Burstein-Moss effect.
23 citations
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TL;DR: This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells, including nanoscale wires, particles and voids.
Abstract: High-performance photovoltaic cells use semiconductors to convert sunlight into clean electrical power, and transparent dielectrics or conductive oxides as antireflection coatings. A common feature of these materials is their high refractive index. Whereas high-index materials in a planar form tend to produce a strong, undesired reflection of sunlight, high-index nanostructures afford new ways to manipulate light at a subwavelength scale. For example, nanoscale wires, particles and voids support strong optical resonances that can enhance and effectively control light absorption and scattering processes. As such, they provide ideal building blocks for novel, broadband antireflection coatings, light-trapping layers and super-absorbing films. This Review discusses some of the recent developments in the design and implementation of such photonic elements in thin-film photovoltaic cells.
835 citations
TL;DR: A double-sided grating design is introduced, where the front and back surfaces of the cell are separately optimized for antireflection and light trapping, respectively, which yields a photocurrent close to the Yablonovitch limit.
Abstract: Enhancing the light absorption in ultrathin-film silicon solar cells is important for improving efficiency and reducing cost We introduce a double-sided grating design, where the front and back surfaces of the cell are separately optimized for antireflection and light trapping, respectively The optimized structure yields a photocurrent of 346 mA/cm(2) at an equivalent thickness of 2 μm, close to the Yablonovitch limit This approach is applicable to various thicknesses and is robust against metallic loss in the back reflector
604 citations
TL;DR: In this article, a review of state-of-the-art anti-reflecting (AR) techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field are presented.
Abstract: Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light. This review presents selected state-of-the-art AR techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field.
565 citations
TL;DR: The inherent performance of these wires thus conceptually allows the development of efficient photovoltaic and photoelectrochemical energy-conversion devices based on a radial junction platform.
Abstract: Silicon wire arrays, though attractive materials for use in photovoltaics and as photocathodes for hydrogen generation, have to date exhibited poor performance. Using a copper-catalyzed, vapor-liquid-solid–growth process, SiCl_4 and BCl_3 were used to grow ordered arrays of crystalline p-type silicon (p-Si) microwires on p^+-Si(111) substrates. When these wire arrays were used as photocathodes in contact with an aqueous methyl viologen^(2+/+) electrolyte, energy-conversion efficiencies of up to 3% were observed for monochromatic 808-nanometer light at fluxes comparable to solar illumination, despite an external quantum yield at short circuit of only 0.2. Internal quantum yields were at least 0.7, demonstrating that the measured photocurrents were limited by light absorption in the wire arrays, which filled only 4% of the incident optical plane in our test devices. The inherent performance of these wires thus conceptually allows the development of efficient photovoltaic and photoelectrochemical energy-conversion devices based on a radial junction platform.
490 citations
Book•
01 Jan 2008
TL;DR: In this article, the surface and interface properties of sputter-deposited ZnO-based thin films are investigated for thin-film solar cells and texture-etched ZnOs for Silicon Thin Film solar cells.
Abstract: ZnO and Its Applications.- Electrical Properties.- Optical Properties of ZnO and Related Compounds.- Surfaces and Interfaces of Sputter-Deposited ZnO Films.- Magnetron Sputtering of ZnO Films.- Zinc Oxide Grown by CVD Process as Transparent Contact for Thin Film Solar Cell Applications.- Pulsed Laser Deposition of ZnO-Based Thin Films.- Texture Etched ZnO:Al for Silicon Thin Film Solar Cells.- Chalcopyrite Solar Cells and Modules.
440 citations