Solar photovoltaic devices

Amorphous Silicon. Amorphous silicon is generally deposited by Reaction (4) at a deposition temperature of 560°C and at low pressure (ca. 1 Torr).P l Helium RF plasma CVD is also commonly used, especially in the production of solar photovoltaic devices. 

The oxidative deterioration of most commercial polymers when exposed to sunlight has restricted their use in outdoor applications. A novel approach to the problem of predicting 20-year performance for such materials in solar photovoltaic devices has been developed in our laboratories. The process of photooxidation has been described by a qualitative model, in terms of elementary reactions with corresponding rates. A numerical integration procedure on the computer provides the predicted values of all species concentration terms over time, without any further assumptions. In principle, once the model has been verified with experimental data from accelerated and/or outdoor exposures of appropriate materials, we can have some confidence in the necessary numerical extrapolation of the solutions to very extended time periods. Moreover, manipulation of this computer model affords a novel and relatively simple means of testing common theories related to photooxidation and stabilization. The computations are derived from a chosen input block based on the literature where data are available and on experience gained from other studies of polymer photochemical reactions. Despite the problems associated with a somewhat arbitrary choice of rate constants for certain reactions, it is hoped that the study can unravel some of the complexity of the process, resolve some of the contentious issues and point the way for further experimentation. 

Absorber - The component of a solar thermal collector that absorbs solar radiation and converts it to heat, or, as in a solar photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes). 

Absorption Coefficient - In reference to a solar energy conversion devices, the degree to which a substance will absorb solar energy. In a solar photovoltaic device, the factor by which photons are absorbed as they travel a unit distance through a material. 

Chemical Vapor Deposition (CVD) - A method of depositing thin semiconductor films used to make certain types of solar photovoltaic devices. With this method, a substrate is exposed to one or more... 

Epitaxial Growth - In reference to solar photovoltaic devices, the growth of one crystal on the surface of another crystal. The growth of the deposited crystal Is oriented by the lattice structure of the original crystal. 

Intrinsic Layer - A layer of semiconductor material (as used in a solar photovoltaic device) whose properties are essentially those of the pure, undoped, material. 

Photovoltaic Device - A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semi-conductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multi-crystalline, or amorphous forms. 

Ribbon (Photovoltaic) Cells - A type of solar photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material. 

Silicon - A chemical element, of atomic number 14, that is semi-metallic, and an excellent semiconductor material used in solar photovoltaic devices commonly found In sand. 

Solar Cell - A solar photovoltaic device with a specified area. 

Solar Module (Panel) - A solar photovoltaic device that produces a specified power output under defined test conditions, usually composed of groups of solar cells connected In series, in parallel, or In series-parallel combinations. 

The remarkable efficiency of reaction-center photochemistry has encouraged the design and the study of synthetic models. Most research on artificial photosynthesis has been directed toward mimicry of the natural reaction center (RC). The center functions as a molecular-scale solar photovoltaic device that converts light energy into chemical energy that can be transported and stored for maintenance, growth, and... 

Single-Crystal Silicon. Silicon is still the dominant material in photovoltaic. It has good efficiency, which is 25% in theory and 15% in actual practice. Silicon photovoltaic devices are made from wafers sliced from single crystal silicon ingots, produced in part by CVD (see Ch. 8, Sec. 5.1). However, silicon wafers are still costly, their size is limited, and they cannot be sliced to thicknesses less than 150 im. One crystalline silicon wafer yields only one solar cell, which has an output of only one watt. This means that such cells will always be expensive and can only be used where their high efficiency is essential and cost is not a major factor such as in a spacecraft applications. 

Concerning the photovoltaic devices, when subjected to solar emission at AM 1.5, the short-circuit current (Isc) signals were 480,530, and 600 pA for Morus nigra, Morus nigra plus P-carotene and Mix, respectively. This means that the best performances were observed in the case of the blend of all organic derivatives used. 

Metal chalcogenide semi-conducting materials have found many applications in opto-electronic, solar cell and photovoltaic devices. Deposition of these materials can be achieved by a variety of techniques of which one of the most... 

The conversion of light to electric current in photovoltaic devices is the direct inversion of the electroluminescent process in OLEDs, thus it is not surprising that the same molecular glasses as described above have also been used for the realization of solar cells. There are at least two different types of approaches, however, that shall be described now. 

Kymakis E, Amaratunga GAJ (2003). Photovoltaic cells based on dye-sensitisation of single-wall carbon nanotubes in a polymer matrix. Solar Ener. Mater. Solar Cells 80 465 172.Kymakis E, Alexandrou I, Amaratunga GAJ (2003). High open-circuit voltage photovoltaic devices from carbon-nanotube-polymer composites. J. Appl. Phys. 93 1764-1768. 

Gratzel, M. Highly efficient nanocrystalUne photovoltaic devices. Plat. Met. Rev., 1994, 38, 151-159 Gratzel, M. Dye-sensitized solar cells, J. Photochem. Photobiol. C-Photochem. Rev., 2003, 4(2), 145-153. 

The preceding sections described molecular interactions important in organic solar cells. This section discusses the impact of those interactions on the overall device behavior. Simulated electrical behavior for a typical solar cell is illustrated in Fig. 10. Under forward bias voltages 0 < V < Vqo typical photovoltaic device under illumination supplies power (P = / x V) to the external circuit (cf. lower panel of Fig. 10, dashed trace in first quadrant). The formalism used here implies that, under reverse bias, the organic material is reduced at the anode and oxidized at the cathode, while, under forward bias, the organic material is oxidized at the anode and reduced at the cathode. The short circuit current, J c, is approximately equal to... 

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