Photovoltaic process

Concentrated Photovoltaic (CPV) A technology in which the use of mirrors, lenses or other items concentrate and thus vastly increase the intensity of sunlight during the photovoltaic process. 

The photovoltaic process is just the reverse process utilized in light-emitting devices. Thus, the experience gained in LEDs is useful in the development of photovoltaic devices. 

PEC effects, and therefore cells, can exist in two forms - photovoltaic (PV) and photogalvanic (PG) - the latter of which shall be discussed extensively within this review. A third type of PEC cell has been proposed by Tien et al. [6] which combines the effects of the photogalvanic and photovoltaic processes and is subsequently named the photogalvanovoltaic effect. However, the feasibility of using this process as a commercial application is questionable, and research into photogalvanovoltaic cells is extremely limited [7, 8]. 

Yet another development, at the University of Toronto in Canada, is based on the discovery of the first plastic material to absorb infra red light. This achievement came about as a result of doping a polymer with nanometre-sized semiconductor particles that were tuned to absorb in the infra red region of the frequency spectrum. Not only had the research team discovered what was claimed to be the world s first infra red detector which could be painted but also the world s first infra red photovoltaic detector. The researchers believe that, by combining infra red and visible photovoltaic processes, it could be possible to reduce the cost of solar energy since the current 6% best efficiency figure for plastic solar cells might even be raised to 30%. 

In the early 1970s, the first companies to apply low cost, mass production techniques to photovoltaics, a technology that had previously been considered an exotic aerospace technology, emerged. These techniques included the use of electroplated and screen printed metal paste electrical conductors, reflow soldered ribbon interconnects, and by 1977, low cost, automobile windshield-style, laminated module constmction. Such processes benefitted from a substantial existing industrial infrastmcture, and have become virtually ubiquitous in the present PV industry. 

Thus, CIS is a promising photovoltaic material, but improved processing techniques are needed to achieve commercial production of advanced high efficiency CIS alloy materials. Table 1 summarizes the laboratory and commercial status of significant PV technology. 

Another growing apphcation that overlaps the electrically functional area is the use of transparent conductive coatings or tin oxide, indium—tin oxide, and similar materials in photovoltaic solar ceUs and various optic electronic apphcations (see Photovoltaic cells). These coatings are deposited by PVD techniques as weU as by spray pyrolysis, which is a CVD process. 

Zinc—bromine storage batteries (qv) are under development as load-leveling devices in electric utilities (64). Photovoltaic batteries have been made of selenium or boron doped with bromine. Graphite fibers and certain polymers can be made electrically conductive by being doped with bromine. Bromine is used in quartz—haUde light bulbs. Bromine is used to etch aluminum, copper, and semi-conductors. Bromine and its salts are known to recover gold and other precious metals from their ores. Bromine can be used to desulfurize fine coal (see Coal conversion processes). Table 5 shows estimates of the primary uses of bromine. 

In low-dimensional systems, such as quantum-confined. semiconductors and conjugated polymers, the first step of optical absorption is the creation of bound electron-hole pairs, known as excitons [34). Charge photogcncration (CPG) occurs when excitons break into positive and negative carriers. This process is of essential importance both for the understanding of the fundamental physics of these materials and for applications in photovoltaic devices and photodctcctors. Since exciton dissociation can be affected by an external electric field, field-induced spectroscopy is a powerful tool for studying CPG. 

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