Photovoltaic materials material issues

Other important properties for photovoltaic materials are their refractive index, stability, brittleness, toxicity, crystal lattice constant, thermal expansion coefficient, temperatures required for processing into cells, energy investment for cell production, ability to be doped both types, level of technological knowledge and industrial maturity, cost, and abundance. Issues particular to passivation and the trapping of weakly absorbed light include the availability of compatible and affordable passivation and surface texturing methods. ... 

Now, consider stability. If a satisfactory initial system or component performance and cost are assumed, then in many cases the critical issue is to maintain the physical behavior of materials adjoining an interface for up to 30 years. The physical behavior may include properties that directly influence solar device performance, such as reflectance, transmittance, absorptance, emittance, and photovoltaic efficiency or solar device performance may be indirectly affected by properties such as adhesion, permeability, photo-oxidative stability, or interdiffusion. The required stability of interfaces in SECS components is counter to basic physics and chemistry, because atoms at interfaces must be more reactive and thermodynamically less stable than when in the bulk of materials (2). Yet, the density of solar energy requires deploying systems with large interfacial... 

Photovoltaics also require significant research activity in the chemical sciences. Low-cost methods are required for producing solar-grade silicon for photovoltaic cells. Better solar cell materials are needed than the presently utilized amorphous silicon. These materials must be more efficient without the use of heavy metals such as cadmium, tellurium, indium, and lead, which present significant environmental issues. An understanding of the degradation process of photovoltaic cells is needed, as is an answer to why these materials lose their effectiveness after prolonged exposure to the sun. Finally, there is a need to develop catalysts for the efficient photochemical conversion of water. 

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. 

The efficiency of photovoltaic devices depends on both the photoin-duced charge generation, which is based on the electron transfer efficiency and the transport of charges created to the electrodes, i.e., the charge carrier mobility. These two issues must be fulfilled simultaneously. It is possible to construct a structural arrangement of the device materials in order to enhance both demands in a microscopic region separately. 

Reclamatimi of materials will become an issue with the widespread deployment of compound semiconductor photovoltaics [31, 32]. Electrochemical dissolutimi and reclamation of the elements in CIS, CdS, and CdTe have been proposed as a recycling process. 

Miles, R. W. Forbes, H. I. An overview of state-of-the-art cell development and environmental issues. Progress in Crystal Growth and Characterization of Materials. Photovoltaic Solar Cells, 2005, 51, 1 2. 

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