Matching Items (20)

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Waste Management and Equipment Design of Recycling Solar Cells

Description

In Professor Meng Tao and Wen-His Huang's paper's [1,2] the recycling process to create a sustainable Photovoltaic (PV) industry is laid out. The process utilized to recycle the materials requires

In Professor Meng Tao and Wen-His Huang's paper's [1,2] the recycling process to create a sustainable Photovoltaic (PV) industry is laid out. The process utilized to recycle the materials requires the use of three semi-problematic chemicals including: Sodium Hydroxide (NaOH), Nitric Acid (HNO3), and Hydrofluoric Acid (HF). By utilizing a combination of reverse osmosis filtration, pre-lime treatment, neutralization by combination, and mineral specific filtering the chemicals can either by recycled as Environmental Protection Agency (EPA) standardized waste water or profitable byproducts such as Sodium Nitrate (NaNO3). For the recycling of hydrofluoric acid, a combination of pre-lime coagulation, microfiltration and a spiral wound reverse osmosis (RO) system, less than 1mg/L in line with national standards for human consumption. The sodium hydroxide and nitric acid recycling process handles more contaminants that just the byproduct of the chemicals and manages this through a combination of multi-stage flash/vapor distillation along with a reverse osmosis filtration system. By utilizing both systems of recycling, a completely closed loop system for recycling silicon solar cells is laid out and creates a new standard for clean energy management.

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  • 2016-12

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Electroplating of Aluminium on Silicon in an Ionic Liquid

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Electroplating of aluminum (Al) on silicon (Si) substrates has been demonstrated in an above-room-temperature ionic liquid for the metallization of wafer-Si solar cells. The electrolyte was prepared by mixing anhydrous

Electroplating of aluminum (Al) on silicon (Si) substrates has been demonstrated in an above-room-temperature ionic liquid for the metallization of wafer-Si solar cells. The electrolyte was prepared by mixing anhydrous aluminum chloride and 1-ethyl-3-methylimidazolium tetrachloroaluminate. The plating was carried out by means of galvanostatic electrolysis. The structural and compositional properties of the Al deposits were characterized, and the sheet resistance of the deposits revealed the effects of pre-bake conditions, deposition temperature, and post-deposition annealing conditions. It was found that dense, adherent Al deposits with resistivity in the high 10-6 Ω-cm range can be reproducibly obtained directly on Si substrates.

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  • 2014-11-30

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Tuning the band gap of hematite alpha-Fe2O3 by sulfur doping

Description

Based on the density functional theory, the band structure and optical absorption of the isovalent sulfur-doped hematite alpha-Fe2O3 are studied systematically. The results show that the band gap of alpha-Fe2O3-xSx

Based on the density functional theory, the band structure and optical absorption of the isovalent sulfur-doped hematite alpha-Fe2O3 are studied systematically. The results show that the band gap of alpha-Fe2O3-xSx decreases monotonically with increasing the sulfur concentration, resulting in an obvious increase of the optical absorption edge in the visible range. Most intriguingly, unlike the pure alpha-Fe2O3 material, the alpha-Fe2O3-xSx with x approximate to 0.17 (S concentration of similar to 5.6%) exhibits a direct band gap of an ideal value (similar to 1.45 eV), together with high optical absorption (similar to 10(5) cm(-1)) and lower carriers effective masses. These results indicate that alpha-Fe2O3-xSx, with a proper concentration of sulfur, may serve as a promising candidate for low-cost solar-cell materials.

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  • 2013-09-05

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Silver Recovery from Silver Fluoride Solution for Solar Module Recycling

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As Energy needs grow and photovoltaics expand to meet humanity’s demand for electricity, waste modules will start building up. Tao et. al. propose a recycling process to recover all precious

As Energy needs grow and photovoltaics expand to meet humanity’s demand for electricity, waste modules will start building up. Tao et. al. propose a recycling process to recover all precious solar cell materials, a process estimated to generate a potential $15 billion in revenue by 2050. A key part of this process is metal recovery, and specifically, silver recovery. Silver recovery via electrowinning was studied using a hydrofluoric acid leachate/electrolyte. Bulk electrolysis trials were performed at varied voltages using a silver working electrode, silver pseudo-reference electrode and a graphite counter-electrode. The highest mass recovery achieved was 98.8% which occurred at 0.65 volts. Product purity was below 90% for all trials and coulombic efficiency never reached above 20%. The average energy consumption per gram of reduced silver was 2.16kWh/kg. Bulk electrolysis indicates that parasitic reactions are drawing power from the potentiostat and limiting the mass recovery of the system. In order to develop this process to the practical use stage, parasitic reactions must be eliminated, and product purity and power efficiency must improve. The system should be run in a vacuum environment and the reduction peaks in the cell should be characterized using cyclic voltammetry.

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  • 2020-12

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Characterization of Al/Si Junctions on Si(100) Wafers With Chemical Vapor Deposition-Based Sulfur Passivation

Description

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky barriers are characterized with current–voltage (I–V), capacitance–voltage (C–V) and activation-energy methods. Al/S-passivated n-type Si(100) junctions exhibit ohmic behavior with a barrier height of <0.078 eV by the I–V method and significantly lower than 0.08 eV by the activation-energy method. For Al/S-passivated p-type Si(100) junctions, the barrier height is ~0.77 eV by I–V and activation-energy methods and 1.14 eV by the C–V method. The discrepancy between C–V and other methods is explained by image force-induced barrier lowering and edge-leakage current. The I–V behavior of an Al/S-passivated p-type Si(100) junction remains largely unchanged after 300 °C annealing in air. It is also discovered that heating the S-passivated Si(100) wafer before Al deposition significantly improves the thermal stability of an Al/S-passivated n-type Si(100) junction to 500 °C.

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  • 2014-09-01

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Electrical and thermal transport in alternative device technologies

Description

The goal of this research work is to develop a particle-based device simulator for modeling strained silicon devices. Two separate modules had to be developed for that purpose: A generic

The goal of this research work is to develop a particle-based device simulator for modeling strained silicon devices. Two separate modules had to be developed for that purpose: A generic bulk Monte Carlo simulation code which in the long-time limit solves the Boltzmann transport equation for electrons; and an extension to this code that solves for the bulk properties of strained silicon. One scattering table is needed for conventional silicon, whereas, because of the strain breaking the symmetry of the system, three scattering tables are needed for modeling strained silicon material. Simulation results for the average drift velocity and the average electron energy are in close agreement with published data. A Monte Carlo device simulation tool has also been employed to integrate the effects of self-heating into device simulation for Silicon on Insulator devices. The effects of different types of materials for buried oxide layers have been studied. Sapphire, Aluminum Nitride (AlN), Silicon dioxide (SiO2) and Diamond have been used as target materials of interest in the analysis and the effects of varying insulator layer thickness have also been investigated. It was observed that although AlN exhibits the best isothermal behavior, diamond is the best choice when thermal effects are accounted for.

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Date Created
  • 2013

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Codoped zinc oxide by a novel co-spray deposition technique for solar cells applications

Description

Zinc oxide (ZnO), a naturally n-type semiconductor has been identified as a promising candidate to replace indium tin oxide (ITO) as the transparent electrode in solar cells, because of its

Zinc oxide (ZnO), a naturally n-type semiconductor has been identified as a promising candidate to replace indium tin oxide (ITO) as the transparent electrode in solar cells, because of its wide bandgap (3.37 eV), abundant source materials and suitable refractive index (2.0 at 600 nm). Spray deposition is a convenient and low cost technique for large area and uniform deposition of semiconductor thin films. In particular, it provides an easier way to dope the film by simply adding the dopant precursor into the starting solution. In order to reduce the resistivity of undoped ZnO, many works have been done by doping in the ZnO with either group IIIA elements or VIIA elements using spray pyrolysis. However, the resistivity is still too high to meet TCO's resistivity requirement. In the present work, a novel co-spray deposition technique is developed to bypass a fundamental limitation in the conventional spray deposition technique, i.e. the deposition of metal oxides from incompatible precursors in the starting solution. With this technique, ZnO films codoped with one cationic dopant, Al, Cr, or Fe, and an anionic dopant, F, have been successfully synthesized, in which F is incompatible with all these three cationic dopants. Two starting solutions were prepared and co-sprayed through two separate spray heads. One solution contained only the F precursor, NH 4F. The second solution contained the Zn and one cationic dopant precursors, Zn(O 2CCH 3) 2 and AlCl 3, CrCl 3, or FeCl 3. The deposition was carried out at 500 &degC; on soda-lime glass in air. Compared to singly-doped ZnO thin films, codoped ZnO samples showed better electrical properties. Besides, a minimum sheet resistance, 55.4 &ohm;/sq, was obtained for Al and F codoped ZnO films after vacuum annealing at 400 &degC;, which was lower than singly-doped ZnO with either Al or F. The transmittance for the Al and F codoped ZnO samples was above 90% in the visible range. This co-spray deposition technique provides a simple and cost-effective way to synthesize metal oxides from incompatible precursors with improved properties.

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Date Created
  • 2013

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Novel materials, grid design rule, and characterization methods for multi-junction solar cells

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This dissertation addresses challenges pertaining to multi-junction (MJ) solar cells from material development to device design and characterization. Firstly, among the various methods to improve the energy conversion efficiency of

This dissertation addresses challenges pertaining to multi-junction (MJ) solar cells from material development to device design and characterization. Firstly, among the various methods to improve the energy conversion efficiency of MJ solar cells using, a novel approach proposed recently is to use II-VI (MgZnCd)(SeTe) and III-V (AlGaIn)(AsSb) semiconductors lattice-matched on GaSb or InAs substrates for current-matched subcells with minimal defect densities. CdSe/CdTe superlattices are proposed as a potential candidate for a subcell in the MJ solar cell designs using this material system, and therefore the material properties of the superlattices are studied. The high structural qualities of the superlattices are obtained from high resolution X-ray diffraction measurements and cross-sectional transmission electron microscopy images. The effective bandgap energies of the superlattices obtained from the photoluminescence (PL) measurements vary with the layer thicknesses, and are smaller than the bandgap energies of either the constituent material. Furthermore, The PL peak position measured at the steady state exhibits a blue shift that increases with the excess carrier concentration. These results confirm a strong type-II band edge alignment between CdSe and CdTe. The valence band offset between unstrained CdSe and CdTe is determined as 0.63 eV±0.06 eV by fitting the measured PL peak positions using the Kronig-Penney model. The blue shift in PL peak position is found to be primarily caused by the band bending effect based on self-consistent solutions of the Schrödinger and Poisson equations. Secondly, the design of the contact grid layout is studied to maximize the power output and energy conversion efficiency for concentrator solar cells. Because the conventional minimum power loss method used for the contact design is not accurate in determining the series resistance loss, a method of using a distributed series resistance model to maximize the power output is proposed for the contact design. It is found that the junction recombination loss in addition to the series resistance loss and shadowing loss can significantly affect the contact layout. The optimal finger spacing and maximum efficiency calculated by the two methods are close, and the differences are dependent on the series resistance and saturation currents of solar cells. Lastly, the accurate measurements of external quantum efficiency (EQE) are important for the design and development of MJ solar cells. However, the electrical and optical couplings between the subcells have caused EQE measurement artifacts. In order to interpret the measurement artifacts, DC and small signal models are built for the bias condition and the scan of chopped monochromatic light in the EQE measurements. Characterization methods are developed for the device parameters used in the models. The EQE measurement artifacts are found to be caused by the shunt and luminescence coupling effects, and can be minimized using proper voltage and light biases. Novel measurement methods using a pulse voltage bias or a pulse light bias are invented to eliminate the EQE measurement artifacts. These measurement methods are nondestructive and easy to implement. The pulse voltage bias or pulse light bias is superimposed on the conventional DC voltage and light biases, in order to control the operating points of the subcells and counterbalance the effects of shunt and luminescence coupling. The methods are demonstrated for the first time to effectively eliminate the measurement artifacts.

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Date Created
  • 2012

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Development of silver-free silicon photovoltaic solar cells with all-aluminum electrodes

Description

To date, the most popular and dominant material for commercial solar cells is

crystalline silicon (or wafer-Si). It has the highest cell efficiency and cell lifetime out

of all commercial solar cells.

To date, the most popular and dominant material for commercial solar cells is

crystalline silicon (or wafer-Si). It has the highest cell efficiency and cell lifetime out

of all commercial solar cells. Although the potential of crystalline-Si solar cells in

supplying energy demands is enormous, their future growth will likely be constrained

by two major bottlenecks. The first is the high electricity input to produce

crystalline-Si solar cells and modules, and the second is the limited supply of silver

(Ag) reserves. These bottlenecks prevent crystalline-Si solar cells from reaching

terawatt-scale deployment, which means the electricity produced by crystalline-Si

solar cells would never fulfill a noticeable portion of our energy demands in the future.

In order to solve the issue of Ag limitation for the front metal grid, aluminum (Al)

electroplating has been developed as an alternative metallization technique in the

fabrication of crystalline-Si solar cells. The plating is carried out in a

near-room-temperature ionic liquid by means of galvanostatic electrolysis. It has been

found that dense, adherent Al deposits with resistivity in the high 10^–6 ohm-cm range

can be reproducibly obtained directly on Si substrates and nickel seed layers. An

all-Al Si solar cell, with an electroplated Al front electrode and a screen-printed Al

back electrode, has been successfully demonstrated based on commercial p-type

monocrystalline-Si solar cells, and its efficiency is approaching 15%. Further

optimization of the cell fabrication process, in particular a suitable patterning

technique for the front silicon nitride layer, is expected to increase the efficiency of

the cell to ~18%. This shows the potential of Al electroplating in cell metallization is

promising and replacing Ag with Al as the front finger electrode is feasible.

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Date Created
  • 2016

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Development of New Front Side Metallization Method of Aluminum Electroplating for Silicon Solar Cell

Description

In this thesis, the methods of aluminum electroplating in an ionic liquid for silicon solar cell front side metallization were studied. It focused on replacing the current silver screen printing

In this thesis, the methods of aluminum electroplating in an ionic liquid for silicon solar cell front side metallization were studied. It focused on replacing the current silver screen printing with an alternative metallization technology using a low-cost Earth-abundant metal for mass production, due to the high cost and limited availability of silver. A conventional aluminum electroplating method was employed for silicon solar cells fabrication on both p-type and n-type substrates. The highest efficiency of 17.9% was achieved in the n-type solar cell with a rear junction, which is comparable to that of the same structure cell with screen printed silver electrodes from industrial production lines. It also showed better spiking resistant performance than the common structure p-type solar cell. Further efforts were put on the development of a novel light-induced plating of aluminum technique. The aluminum was deposited directly on a silicon substrate without the assistance of a conductive seed layer, thus simplified and reduced the process cost. The plated aluminum has good adhesion to the silicon surface with the resistivity as low as 4×10–6 -cm. A new demo tool was designed and set up for the light-induced plating experiment, aiming to utilize this technique in large-size solar cells fabrication and mass production. Besides the metallization methods, a comprehensive sensitivity analysis for the efficiency dispersion in the production of crystalline-Si solar cells was presented based on numerical simulations. Temperature variation in the diffusion furnace was the most significant cause of the efficiency dispersion. It was concluded that a narrow efficiency range of ±0.5% absolute is achievable if the emitter diffusion temperature is confined to a 13˚C window, while other cell parameters vary within their normal windows. Possible methods to minimize temperature variation in emitter diffusion were proposed.

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Date Created
  • 2018