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I will describe principles and advantages of the growth of semiconductor nanowires, specifically as applied to fabrication of light-emitting diodes for display and solid state lighting applications as well as for the realization of nanowire array solar cells.
Photovoltaic (PV) modules based on silicon solar cells are widely used to convert solar energy into electrical energy. The energy output of these modules is very low due to their low power conversion efficiencies of approximately 15%. Reflectors are used to improve the power output of PV modules, by increasing the effective capture area. The performance of the solar panel with reflector depends mainly...
We report photovoltaic energy conversion in atomically thin crystals. We present two device concepts: (i) a lateral p-n junction diode, based on a WSe2 atomic monolayer, where the junction is formed by electrostatic doping using a pair of oppositely biased gate electrodes. (ii) a MoS2/WSe2 van der Waals heterostructure, that utilizes different electron affinities of both materials for the separation...
We use titanium nitride (TiN) to demonstrate an ultra-thin plasmonic thermal emitter operating at high temperatures (830 K). The spectrally selective emitter exhibits a large emittance at around 2.5 µm and below, and suppresses emission at longer wavelengths.
Controlled nanostructuring of thin-film solar cells offers a promising route toward increased efficiency through improved light trapping. Many such light trapping designs involve structuring of the active region itself. Optimization of these designs is aided by the use of computer simulations that account for both the optics and electronics of the device. We describe such a simulation-based approach...
In this paper, we quantitatively evaluate the relative importance of three mechanisms that are proffered by various groups to interpret the effects of sodium (Na) incorporation in copper indium gallium diselenide solar cells. The suggested mechanisms are 1) increase in the carrier density due to defect passivation; 2) spatial redistribution of gallium (Ga); and 3) change in the crystal orientation...
The limiting efficiency for photovoltaic energy conversion based on a semiconductor pn-junction is typically determined using the method of detailed balance put forth by Shockley and Queisser. Here we describe how this theory is altered in the presence of a photonic structure that is capable of modifying the absorption and emission of photons. By incorporating specifically designed photonic structures,...
Poor carrier mobility in organic semiconductors and high free carrier recombination at the polymer interfaces hinder efficient collection of photogenerated carriers in organic photovoltaic (OPV) devices. This inefficiency in charge collection is reflected in the low fill factor (FF) of the OPV cells (FFOPV ∼ 65%) compared with its inorganic counterparts (FF ∼ 85%). In this paper, we show that the...
A spectroscopic ellipsometry (SE) capability having the potential to scan production-scale areas at high speed has been developed and successfully applied to map the alloy composition of copper-indium-gallium-diselenide (CuIn1−xGaxSe2: CIGS) thin films. This technique not only generates a compositional map but simultaneously provides maps of the more typical SE-determined properties as well, including...
We optimized Ag/ZnO back reflectors (BR) for hydrogenated nanocrystalline silicon (nc-Si:H) solar cells by independently changing the textures of the Ag and ZnO layers. We found that Ag/ZnO with textured Ag and thin ZnO provides the highest nc-Si:H solar cell efficiency. Optimized Ag texture with an rms = 40 nm effectively scatters light without seriously degrading the nc-Si:H material quality. Using...
Terahertz (THz) has been well known for its unique ability to propagate through non-polar packaging material. At the same time, THz wavelengths are small enough to provide meaningful imaging resolution, leading to their large potential in non-destructive evaluation. Correlation processing is a technique that has been shown to detect phase resonances in illicit chemicals, and in this paper, is extended...
In this paper, we report the simulation of electrical field distribution and growth of gradient arrayed TiO2 nanotubes by electrochemical anodization. A rectangle electrochemical electrode configuration, in which the end of cathode (Pt wire) is perpendicularly pointed to anode surface (Ti foil), is applied in NH4F glycol electrolyte. Electric field distribution on the surface of the titanium foil...
Titanium dioxide (TiO2) has high optical refractive index and is transparent to visible light. No strong reflection is expected from a single layer of continuous TiO2 film. In this work, we report the unusually high reflection from a thick layer of TiO2 nanoparticles. TiO2 nanoparticles of different sizes (~ 21 nm and ~ 400 nm) were deposited on indium tin oxide (ITO) coated glass substrate by electrophoretic...
Enhancing conversion efficiency is the main object in the photovoltaic technology of solar cells. III-V semiconductors, InGaN alloy are very encouraging candidates for solar cells. In recent years, InGaN alloy provides the ability to tune the band gap for solar energy conversion. In this work, InGaN based QW and QD solar cells have been theoretically studied and evaluated the performance with various...
Thin-film CdTe is one of the leading materials for high efficiency, low-cost and stable PV cells. The formation of a stable, low resistance, non-rectifying back contact to p-CdTe thin-film is the most critical challenge associated with this technology, another main constraint of PV technology is its high cost. To reduce the cost, less material consumption is desirable. Thus research is leading toward...
The main objective of this paper is to increase the efficiency of the multi-junction solar cell. In general, the efficiency of the multi-junction solar cell depends upon various design parameters such as material type, thickness of the layers, doping concentration, type of texturing and thickness of anti-reflective coating. The performances of the solar cells are determined by using one-dimensional...
In amorphous hydrogenated silicon carbide (a-SiC:H) based p-i-n type solar cells, the device performance is limited by various factors. Most important of which is defects in the i-layer and particularly in the p/i interface. We performed I-V measurements on amorphous solar cells in the structure p(a-SiC H)/i(a-SiC:H)/n(a-Si:H) at AM1.5. All parameters are determined such as efficiency and filling...
Plasmonic core-shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve maximum enhancement, the morphology of PCSNPs needs to be optimized. Here we precisely control the morphology of Au@TiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. Enhancement mechanism was found to vary with the...
A 4.4 % RF-sputtered Cu2ZnSnSe4 thin film solar cell was studied by transmittance electron microscopy (TEM) and photoluminescence (PL). The result reveals non-uniform elemental distribution and large potential fluctuation mainly induced by CuZn defect.
A solar cell or photovoltaic cell is a device which generates electricity directly from visible light. However, the Gratzel solar cells' efficiency is fairly low. So, it costs expensive according to other energy resources products. There is several factors affect gratzel solar cell efficiency which formed from chlorophyll. This research work is a comparative study between Grätzel chlorophyll solar...
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