Production process, photovoltaic

Cells made from GaAs are more costly than silicon cells, because the production process is not as well developed, and gallium and arsenic are not abundant materials. GaAs cells have been used when very high efficiency is needed regardless of cost such as required in space applications. They were also used in the Sunraycer, a photovoltaic-powered electric car, which won the Pentax World Solar Challenge race for solar-powered vehicles in 1987. It ran the 3000-km from Darwin to Adelaide, Australia at an average day time speed of 66-km per hour. The 1990 race was won by a... 

The goal of polymers in photovoltaic cells is to make very cheap active materials even if their efficiency is very low. So, a cheap mass-production process could lead to domestic and industrial applications. Some research dates back 20 years and today several techniques are competing, with either hybrid or all-polymer systems. Among the various methods we can quote as examples ... 

The interfaces of importance in SECS are the solid/solid (S/S), solid/gas (S/G), and solid/ liquid (S/L) (4). The area-intensive nature of SECS components was established in the previous section. The major problem is collecting solar energy at a cost that is competitive with other energy forms. Thus, low initial cost is required for the materials, support structures, and production processes in the SECS of interest in Fig. 1 (6). This requires, for example, using thin films in mirrors, in photovoltaic systems, for antireflection coatings on windows, for passive collection, etc. in addition, these films must be made from inexpensive, durable, and easily processed materials (5). Inexpensive long-life materials in flat-plate collectors and durable, stable absorber coatings are also necessary. 

Trace-Element Characterization of Silicon. In order to define "solar grade" silicon with sufficient precision to make the optimum economic choice among possible production processes, Davis et al. doped a series of silicon ingots with single transition metal impurities and produced curves relating normalized photovoltaic efficiency to the concentration of the contaminant (36). Establishing the x-axis of these curves was not entirely straightforward. As a contribution to this work, NBS measured concentrations of a number of dopants in these samples, with the detection limits found in Table I. An illustration of the difficulty faced in this work is that forty percent of the concentrations determined at NBS differed from the nominal concentration by a factor of two or more. 

Vacuum lamination of terrestrial photovoltaic modules is a new production process requiring special equipment and a significant material development effort. Equipment design studies resulted in improved control and lower costs when using a double-chamber vacuum laminator. Application testing of new materials and primers showed the feasibility of two different back sheet materials, one encapsulant, two new primers for polymers and one primer for metals. 

Suitability for Mass Production. Thin film organic polymers have unique potential for the low-cost large-area mass production of photovoltaic devices. Small amounts of Inexpensive material are required and mass production fabrication processes similar to those already used In the polymer converting Industry, Including film manufacture, lamination, metal coating, and printing, may be applicable. This Is one of the major attractions of a thin film organic polymer photovoltaic device. 

Thin film solar cells in general require a minimum of material and energy input. This is an important fact in view of availability of materials and pay-back time of solar generators. Thin film technology provides means for large scale production and the feasibility to realize integrated photovoltaic generators by the same production process. 

So far the physical realization of the heterojunction and its optimization in photovoltaic efficiency have been discussed. The production process of a photovoltaic generator and its economical use have to satisfy a momber of additional criteria which involve a) technological procedures for economic cell and module fabrication allowing large scale production and b) material evaluation for substrates, contacts and encapsulation. These criteria result in a variety of fabrication methods, structures of cells and modules, and materials. 

Photovoltaics, e.g. solar cells, are using monocrystalline, multicrystalline or amorphous silicon. The relevant production processes are developed to a high degree of sophistication. 

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. 

The photovoltaics industry could expand rapidly if the efficiency of polycrystalline modules could be increased to 15 percent, if these modules could be built with assurance of reliability over a 10- to 20-year period, and if they could be manufactured for 100 or less per square meter. Solar energy research has been largely directed toward only one of these issues efficiency. All research aimed at reducing manufacturing costs has been done in industry and has been largely empirical. Almost no fundamental engineering research has been done on either the laboratory scale or the pilot plant scale for cost-effective processes for the production of photoconverters. 

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