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A photovoltaic cell, such as a solar cell, is provided which has a higher output voltage than prior cells. The improved cell includes a substrate of doped silicon, a first layer of silicon disposed on the substrate and having opposite doping, and a second layer of silicon carbide disposed on the first layer. The silicon carbide preferably has the same type of doping as the first layer.
A photovoltaic cell array consisting of parallel columns of silicon filaments is described. Each fiber is doped to produce an inner region of one polarity type and an outer region of an opposite polarity type to thereby form a continuous radial semi conductor junction. Spaced rows of electrical contacts alternately connect to the inner and outer regions to provide a plurality of electrical outputs which may be combined in parallel or in series.
The photovoltaic properties of single-crystal Cu2S-CdS heterojunctions have been investigated as a function of heat treatment by detailed measurements of the dependence of short-circuit current on photon energy, temperature, and the state of optical degradation or enhancement. A coherent picture is formulated for the relationship between enhancement and optical degradation, and their effect on the transport of short-circuit photoexcited current and dark, forward-bias current in the cell. Optical degradation in the Cu2S-CdS cell is shown to be closely identical to optical degradation of lifetime in a homogeneous CdS:Cd:Cu crystal, indicating that the CdS:Cu layer near the junction interface controls carrier transport in the cell. It is proposed that both the photoexcited short-circuit current and the dark, forward-bias current are controlled by a tunneling-recombination process through interface states.
Solar energy is the most abundant form of energy in many terrestrial and extraterrestrial environments. Often in extraterrestrial environments sunlight is the only readily available form of energy. Thus the ability to efficiently harness solar energy is one of the ultimate goals in the design of space power systems. The essential component that converts solar energy into electrical energy in a solar energy based power system is the photovoltaic cell. Traditionally, photovoltaic cells are based on a single crystal silicon absorber. While silicon is a well understood technology and yields high efficiency, there are inherent disadvantages to using single crystal materials. The requirements of weight, large planar surfaces, and high manufacturing costs make large silicon cells prohibitively expensive for use in certain applications. Because of silicon s disadvantages, there is considerable ongoing research into alternative photovoltaic technologies. In particular, thin film photovoltaic technologies exhibit a promising future in space power systems. While they are less mature than silicon, the better radiation hardness, reduced weight, ease of manufacturing, low material cost, and the ability to use virtually any exposed surface as a substrate makes thin film technologies very attractive for space applications. The research group lead by Dr. Hepp has spent several years researching copper indium disulfide as an absorber material for use in thin film photovoltaic cells. While the group has succeeded in developing a single source precursor for CuInS2 as well as a unique method of aerosol assisted chemical vapor deposition, the resulting cells have not achieved adequate efficiencies. While efficiencies of 11 % have been demonstrated with CuInS2 based cells, the cells produced by this group have shown efficiencies of approximately 1 %. Thus, current research efforts are turning towards the analysis of the individual layers of these cells, as well as the junctions between them, to determine the cause of the poor yields. As a student of electrical engineering with some material science background, my role in this research is to develop techniques for analyzing the electrical characteristics of the CuInS2 cells. My first task was to design a shadow mask to be used to place molybdenum contacts under a layer of CuInS;! in order to analyze the contact resistance between the materials. In addition, I have also analyzed evaporated aluminum top contacts and have tested various methods of increasing their thicknesses in order to decrease series resistance. More recently I have worked with other members of the research group in reviving a vertical cold-wall reactor for experimentation with CuInS2 quantum dots. As part of that project, I have improved the design for a variable frequency and pulse width square wave generator to be used in driving the precursor injection process. My task throughout the remainder of my tenure is to continue to analyze and develop tools for the analysis of electrical properties of the CuInS2 cells with the ultimate goal of discovering ways to improve the efficiency of our photovoltaic cells. Traditionally, photovoltaic cells are based on a single crystal silicon absorber. While The research group lead by Dr. Hepp has spent several years researching copper indium
Theoretical evaluation of heterojunction photovoltaic cells
We demonstrate an organic photovoltaic cell with a monolithic tandem structure in parallel connection. Transparent multiwalled carbon nanotube sheets are used as an interlayer anode electrode for this parallel tandem. The characteristics of front and back cells are measured independently. The short circuit current density of the parallel tandem cell is larger than the currents of each individual cell. The wavelength dependence of photocurrent for the parallel tandem cell shows the superposition spectrum of the two spectral sensitivities of the front and back cells. The monolithic three-electrode photovoltaic cell indeed operates as a parallel tandem with improved efficiency.
CELCAL computer program helps in optimizing grid patterns for different photovoltaic cell geometries and metalization processes. Five different powerloss phenomena associated with front-surface metal grid pattern on photovoltaic cells.
Cadmium sulfide thin film photovoltaic cells
Cadmium sulfide photovoltaic cells
Study of the effect of charged particle bombardment on silicon photovoltaic cells
A method is disclosed for scribing at least three grid contacts of a photovoltaic cell to electrically isolate them from the grid contact pattern used to collect solar current generated by the cell, and using the scribed segments for determining parameters of the cell by a combination of contact end resistance (CER) measurements using a minimum of three equally or unequally spaced lines, and transmission line modal (TLM) measurements using a minimum of four unequally spaced lines. TLM measurements may be used to determine sheet resistance under the contact, R.sub.sk, while CER measurements are used to determine contact resistivity, .rho..sub.c, from a nomograph of contact resistivity as a function of contact end resistance and sheet resistivity under the contact. In some cases, such as the case of silicon photovoltaic cells, sheet resistivity under the contact may be assumed to be equal to the known sheet resistance, R.sub.s, of the semiconductor material, thereby obviating the need for TLM measurements to determine R.sub.sk.
Cadmium sulfide thin film photovoltaic cells - cadmium sulfide film evaporation, cell testing, improvement, and stability, and plastic and metal substrate cells
A unique safety flasher powered by photovoltaic cells and ultracapacitors has been developed. Safety flashers are used wherever there are needs to mark actually or potentially hazardous locations. Examples of such locations include construction sites, highway work sites, and locations of hazardous operations. Heretofore, safety flashers have been powered by batteries, the use of which entails several disadvantages: Batteries must be kept adequately charged, and must not be allowed to become completely discharged. Batteries have rather short cycle lives, and their internal constituents that react chemically to generate electricity deteriorate (and hence power-generating capacities decrease) over time. The performances of batteries are very poor at low temperatures, which often occur in the circumstances in which safety flashers are most needed. The disposal of batteries poses a threat to the environment. The development of the present photovoltaic/ultracapacitor- powered safety flasher, in which the ultracapacitors are used to store energy, overcomes the aforementioned disadvantages of using batteries to store energy. The ultracapacitors in this flasher are electrochemical units that have extremely high volumetric capacitances because they contain large-surface-area electrodes separated by very small gaps. Ultracapacitors have extremely long cycle lives, as compared to batteries; consequently, it will never be necessary to replace the ultracapacitors in the safety flasher. The reliability of the flasher is correspondingly increased, and the life-of-system cost and the adverse environmental effects of the flasher are correspondingly reduced. Moreover, ultracapacitors have excellent low-temperature characteristics, are maintenance-free, and provide consistent performance over time.
Barrier formation studies of copper sulfide and cadmium sulfide in photovoltaic cells
Spectral response of cuprous sulfide-cadmium sulfide film photovoltaic cell to green light
This Phase II project developed Indium-Gallium-Nitride (InGaN) photovoltaic cells for high-temperature and high-radiation environments. The project included theoretical and experimental refinement of device structures produced in Phase I as well as modeling and optimization of solar cell device processing. The devices have been tested under concentrated air mass zero (AM0) sunlight, at temperatures from 100 degC to 250 degC, and after exposure to ionizing radiation. The results are expected to further verify that InGaN can be used for high-temperature and high-radiation solar cells. The large commercial solar cell market could benefit from the hybridization of InGaN materials to existing solar cell technology, which would significantly increase cell efficiency without relying on highly toxic compounds. In addition, further development of this technology to even lower bandgap materials for space applications would extend lifetimes of satellite solar cell arrays due to increased radiation hardness. This could be of importance to the Departmentof Defense (DoD) and commercial satellite manufacturers.
Cadmium sulfide photovoltaic thin film solar cells
Effect of high energy electron irradiation on surface recombination properties of germanium p-n junction photovoltaic cells