We demonstrate, by numerical solution of Maxwell's equations, near-perfect solar light-trapping and absorption over the 300-1100 nm wavelength band in silicon photonic crystal (PhC) architectures, amenable to fabrication by wet-etching and requiring less than 10 lm (equivalent bulk thickness) of crystalline silicon. These PhC's consist of square lattices of inverted pyramids with sides comprised of various (111) silicon facets and pyramid center-to-center spacing in the range of 1.3-2.5 lm. For a wet-etched slab with overall height H ¼ 10 lm and lattice constant a ¼ 2.5 lm, we find a maximum achievable photo-current density (MAPD) of 42.5 mA/cm 2 , falling not far from 43.5 mA/cm 2 , corresponding to 100% solar absorption in the range of 300-1100 nm. We also demonstrate a MAPD of 37.8 mA/cm 2 for a thinner silicon PhC slab of overall height H ¼ 5 lm and lattice constant a ¼ 1.9 lm. When H is further reduced to 3 lm, the optimal lattice constant for inverted pyramids reduces to a ¼ 1.3 lm and provides the MAPD of 35.5 mA/cm 2. These wetetched structures require more than double the volume of silicon, in comparison to the overall mathematically optimum PhC structure (consisting of slanted conical pores), to achieve the same degree of solar absorption. It is suggested these 3-10 lm thick structures are valuable alternatives to currently utilized 300 lm-thick textured solar cells and are suitable for large-scale fabrication by wet-etching. V
Vertically aligned undoped ZnO and Sb-doped ZnO nanowires have been synthesized on a silicon substrate using the vapor-solid technique, without using a catalyst or predeposited buffer layers. The structure and morphology of the assynthesized nanowires are characterized using X-ray diffraction, scanning and transmission electron microscopies, selected area electron diffraction, and electron dispersive X-ray spectroscopy. The results showed that the use of Si(111) is a critical factor for the growth of vertically aligned nanowires. This is a result of the lattice match on Si (111), which is more favorable with the ZnO lattice structure because the Si(111) surface is hexagonal and has a smaller lattice constant of 3.840 Å . The photoluminescence properties were also investigated at room temperature (300 K). The UV peaks of undoped and Sbdoped ZnO nanowires are located at 3.33 and 3.29 eV, respectively. This redshift of 0.04 eV in the Sb-doped ZnO indicates a reduction of the ZnO band gap caused by the Sb dopant. The temperature-dependent photoluminescence spectra of Sb-doped ZnO nanowires from 10 to 300 K were also examined. This measurement showed that at 10 K several peaks appear, at 3.36, 3.23 and 3.04 eV, which were assigned as acceptor-bound excitons, a donor-acceptor pair and a zinc-vacancy-related peak, respectively. These peaks are shifted with the increase of temperature up to 300 K.
Dye sensitized solar cells (DSSCs) are very sensitive to electrodes, due to either high cost or easy corrosion problems. To minimize these factors, we present DSSCs with cheap carbon nanotubes as counter electrodes. In addition, we suggest replacing the electrolyte (in typical DSSCs) with a solid film of powdered CsSnI3. The electrical behavior (I-Vcharacteristics) of the proposed device has been measured for different shading conditions. In the light of a theoretical model based on the presence of two diodes, the experimental data have been explained, taking into account a new equivalent circuit for the DSSC. These DSSCs may receive different levels of sun radiation, which stimulates the study of partial shading; so, we have studied the effect of different shadow rates on the solar conversion efficiency of a unit of 4-W-connected DSSCs. The validity of the present model has been examined by fitting it intoI-Vcharacteristics at different shading rates.
Recently, the production of polymers loaded with inorganic nanomaterials has been one of the most economical techniques playing a special role in improving the physical and mechanical properties of nanocomposites. Rubbers loaded with different concentrations of carbon nanoparticles (CNPs) were synthesized. The mechanical properties were tested according to standard methods. It was found that the properties of the investigated nanocomposites were improved, depending on the concentration of CNPs in the investigated composite. The optimum concentration was found to be 1.3 vol %. Affine deformation based on the Mooney-Rivilin model was used to visualize the effect of CNPs on the rubber. When polyethylene (PE) was added to rubber/ CNPs at the optimum concentration (12.4 vol %), the modulus, tear resistance, and fatigue life were increased, whereas the tensile strength decreased, and the strain at rupture remained almost same. A crosslink model was used to explain the influence of PE on the rubber/CNP
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