Photovoltaic Applications Solar Cells

Combinations of polythiophenes and Cgo have also been utilised by the Santa Barbara group for more fundamental studies [211, 212], and by the Linkoping group for devices [213]. These devices actually comprise two different poly-thiophenes, poly(3-(4-octylphenyl)-2,2 -bithiophene), polymer II in Fig. 13, and poly(3- 2Lmethoxy-5 -octylphenyl thiophene), POMeOPT. The latter is used because it has a sidegroup reminiscent of anisole, which is known to interact with 

manifesting in a solvatochromic shift. POMeOPT is therefore believed to increase the interaction between the polymeric phases and C ) in the blends. An Al/POMeOPT + PTOPT + C o (1 1 2)/ITO device shows a conversion efficiency of 15% with zero bias (A = 500 nm, 1.5mWcm ) and 60% when a reverse bias of 2 V is applied. 

---

The combination of favorable properties of PANI and TiO opens the possibility for various applications of PANI/TiO nanocomposite materials, such as piezoresistivity devices [41], electrochromic devices [99,118], photoelectrochemical devices [43,76], photovoltaic devices/solar cells [44,50,60,61,93,119], optoelectronic devices/UV detectors [115], catalysts [80], photocatalysts [52,63,74,75,78,84,87,97,104,107,121,122,125], photoelectrocatalysts [122,123], sensors [56,61,65,69,85,86,95,120,124], photoelectrochemical [110] and microbial fuel cells [71], supercapacitors [90,92,100,109,111], anode materials for lithium-ion batteries [101,102], materials for corrosion protection [82,113], microwave absorption materials [77,87,89], and electrorheological fluids [105,106]. In comparison with PANI, the covalently bonded PANI/TiO hybrids showed significant enhancement in optical contrast and coloration efficiency [99]. It was observed that the TiO nanodomains covalently bonded to PANI can act as electron acceptors, reducing the oxidation potential and band gap of PANI, thus improving the long-term electrochromic stability [99]. Colloidal... 

Appiications aerospace, composites, electronics (mostly films and coatings), foam composites, hollow fiber membranes, electronics, fibers, mechanical parts (bearings, piston rings, valve seats, washers), microprocessor chip carriers, non-lubricated applications, nuclear power plants, photosensitive materials for positive imaging, photovoltaic film, solar cells, space shuttle, structural adhesives, ultrafiltration membranes ... 

Inorganic transparent coatings are also used as transparent conductive oxide layers (TCO), which are thin films of optically transparent and electrically conductive material. TCOs are an important component in a number of electronic devices including liquid-crystal displays, OLEDs, touchscreens, photovoltaics, and solar cells. Touch panels of smart phones and tablet PC s and front contact layers in flexible photovoltaics are only a few examples [224]. Some applications, such as solar cells, often require a wider range of transparency beyond visible light to make efficient use of the full solar spectrum. 

While hopes are high, heterogeneous photochemical systems seem not yet to have found major practical application. The photovoltaic cell or solar cell is the only system with important (although specialized) commercial use (see Ref. 343). 

Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point selenium is a p-type semiconductor and is finding many uses in electronic and solid-state applications. 

Photovoltaic systems for specific applications are produced by connecting individual modules in series and parallel to provide the desired voltage and current (Figure 4). Each module is constructed of individual solar cells also connected in series and parallel. Modules are typically available in ratings from a few peak watts to 250 peak watts. 

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. 

Ideally, all photons with a wavelength of about 900 nm or shorter should be harvested and converted to electric current. This limit is derived from thermodynamic considerations showing that the conversion efficiency of any single-junction photovoltaic solar converter peaks at approximately 33% near the threshold energy of lAeV.1 2 There are numerous ways to convert the solar radiation directly into electrical power or chemical fuel. The silicon solar cell is the most efficient in this respect. Nevertheless, the capital cost of such devices is not attractive for large-scale applications. 

This type of sensitizer opens up new avenues for improving the near-IR response of dye-sensitized solar cells. In addition, important applications can be foreseen for the development of photovoltaic windows transmitting part of the visible light. Such devices would remain transparent to the eye, while absorbing enough solar energy photons in the near IR to render efficiencies acceptable for practical applications. 

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... 

Gratzel, M., Perspectives for dye-sensitized nanocrystalline solar cells. Progress in photovoltaics research and applications 2000, 8,171-185. 

For reviews of photovoltaic principles and applications, consult Merrigan, J.A., "Sunlight to Electricity - Prospects for Solar Energy Conversion by Photovoltaics", MIT Press, Cambridge, Mass., 1975 "Solar Cells", C.E. Backus, ed.,... 

---