Crystalline cells

It is noticed that the improvement of solar cells is remarkable, and the efficiencies of Si-single crystal cell and the poly crystalline cell reach 17 % and 12.5 %, respectively. The average cost of solar cell module is 3 per watt, which can be competitive with other conventional power sources [8],... 

Crystalline solar cells are heavy and expensive to manufacture. However, their efficiency in converting sunlight has historically been superior to thin-film. Crystalline cells are constructed with silicon semiconducting materials. 

Electrochemical polishing can be used for metallic materials including metals, alloys, and conductive metallic compounds to get a smooth and shiny surface. Bulk metal materials are normally polycrystalline, which are constructed by the repetition of identical structural units (crystalline cells) in space. The crystal periodicity is disrupted at grain boundaries and metal surfaces. However, their macroproperties are isotropic if the crystal grains are randomly orientated. 

The crystalline structure of the [3 form shows an orthorhombic unitary cell [11] and, like the a form, may assume two limiting ordered and disordered structures, named (3 and (3" respectively. Both the crystalline cells of the y and 8 forms are monoclinic [12]. The 8 form always has some solvent molecules trapped in the crystalline lattice, whereas the y form is empty. As widely reported, the formation of the above crystalline structures and the transitions between them may occur under appropriate thermal conditions either in the solid or from solutions phases [13]. 

Cellulose Homopolysaccharides Hemicelluloses Heteropolysaccharides Crystallinity Cell wall architecture Molecular interactions Cellulose derivatives Cellulose esters Cellulose ethers... 

The efficiency of the traditional crystalline cells (which are sawed laboriously out of pure silicone ingots) has increased from 4 percent to almost 25 percent for laboratory specimen commercial production modules are about 14 percent efficient. The newer thin-film photovoltaic materials have lower efficiencies so far—17.1 percent for laboratory samples and 10 percent for commercial production modules. However, the thin-film materials... 

Transition Temperature - This is a temperature (19°C for 100% homopolymer of tetrafluoro-ethylene) at which the unit crystalline cell of polytetrafluoroethylene changes from triclinic to hexagonal. 

Mineral Crystalline structure Polytype Parameter of crystalline cell a A b A c A /J... 

Employing tapping mode AFM phase contrast to distinguish between crystalline and amorphous cells, we observed in direct space that crystallization occurred in a random manner, cell-by-cell (see Fig. 14). Systematic AFM experiments [35] using samples held at - 23 °C for increasing times showed that the fraction of crystalline cells increased with crystallization time, following a relation which can be approximated by n = oo(l - Here, ttoo and... 

Fig. 14 AFM phase images (1x1 jjim ) showing the variation in the number and the distribution of crystalline cells in a thin PBh-PEO(21.1-4.3) film after crystallization at - 23 °C for a 5 min, b 15 min, and c 120 min, respectively, d Shows the percentage of stiU remaining molten cells as a function of time of crystallization...

As we show in Fig. 15, the independence of the individual crystalline cells can also be tested by local melting via a hot AFM tip. Under appropriate conditions (see [56] for more details), only crystalline cells in direct contact with this hot tip melt while neighboring cells stay crystalline. 

The crystalline structure of PHB is orthorhombic with dimensions of the basic crystalline cell a = 5.76 A, b = 13.20 A, c = 5.96 A. A partially planar zig-zag structure can be formed as a result of the mechanical uniaxial load from the amorphous phase between lamellae [117, 118]. PHB forms extremely thin lamellar crystals, with a thickness comprised between 4 and 7 nm and a prevailing size of 5 nm [98]. 

The main element of a crystalline polymer s structure is the crystalline cell, with various shapes and dimensions, as determining its morphology. 

On the other hand, in a perfect material, reaction (1) cannot occur in the bulk of the material. This would imply the formation of K and X interstitial particles which are not supposed to exist. Such a reaction can only occur on the surfaces where a unit crystalline cell can be created or consumed. Thence the corresponding rate vi is nil V] = 0. (49)... 

Polymers, depending on crystallization conditions, can order themselves according to different crystal unit cells, giving rise to the phenomenon of polymorphism. WAXD is the technique of choice for studying the polymorphism of polymers, because different crystalline phases display different diffractometric patterns. Sometimes, more than one phase coexist in the same material, and the areas of the characteristic peaks of each polymorph allow to quantify the abundance of each phase." By WAXD, the size of crystallites can also be measured from the width of the peak applying the Scherrer equation, and the characteristic dimensions of the crystalline cell can be assessed on the basis of the angular position of the peaks. 

Last, one should not neglect the very simple but all important density. The crystalline cell is usually about 10% more dense than the bulk amorphous polymer. Significant deviations from this density must mean an incorrect model. 

The crystallization rate of PHBV compared with most polymers used in industrial processes is very slow, due to the low nucleation that is a result of its high purity and stereoregularity and the slow nuclear growth rate, resulting from the HV units inclusion in the PHB crystalline cell (Reinsch and Kelley 1996). 

Fig. 10.3. Three types of equidistant crystalline cells with a centered O vacancy for the cubic phase of SrTiOs perovskite (a) simple cubic (sc) (b) face-centered cubic (fee) (c) body-centered cubic (bcc). Sticks between the oxygen and titanium ions indicate the partly covalent bonds between them. To construct the difference electron-density plots, each cell is sectioned along the Ti-O-Ti axis by the plane PP...

For the heterojunction system CdS-Cu S conversion efficiencies as high as 9 % have been demonstrated, a practical method of fabrication technology has been established and operational tests have been performed /3,4/. The results and experience obtained prove the CdS-Cu S thin film solar cell as an alternative to crystalline cells such as Si. The basic structure of the CdS-Cu S thin film solar cell is illustrated in figure 2. 

STRUCTURE Crystallinity Cell type (lattice) Cell dimensions... 

The crystalline cell is constructed from four Nd2Fe,4B units, 68 atoms, respectively. This structure is formed also with other lanthanides, yttrium and thorium. The R ions occupy two distinct crystallographic sites, the iron ions share six non-equivalent sites, while B is located on one site. The positions of the atoms in lattice are given in table 1 (Herbst et al. 1984). 

Materials in the solid phase are generally perceived to be crystalline with atoms arranged periodically on a lattice at positions defined by a symmetry group. This is because in thermodynamic equilibrium the state of lowest free energy is usually an ordered state. However, solid materials can be prepared which are disordered and do not exhibit atomic translational invariance, and as such are called amorphous. Such solids are generally meta-stable with respect to crystallization into one or more ordered phases. Spontaneous recrystallization is inhibited by nucleation barriers which limit the formation of crystalline cells and/or by kinetic effects which inhibit the rate of recrystallization. Both processes tend to be very temperature sensitive, which generally limits the range over which an amorphous solid can be maintained. 

Polyvinyl fluoride is a semicrystalline polymer and has a planar zigzag chain conformation. The extent of the polymer crystallinity is dependent on its polymerization method and thermal history. The degree of crystallinity can vary from 20-60%, apparently as a function of defects in the PVF structure. Studies have indicated the crystalline cell is orthorhombic and contains two monomer units. 

S-A Chen, S-J Lee. Application of molecular-dynamics in determination of conformation change with temperature of poly(3-dodecylthiophene) in crystalline cell. Synth Met 1995 72 253-260. 

WAXS measurements were taken at the different orientation of film position relative to X-ray irradiation beam. For all samples, the dififracto-grams reveal the existence of axial cylindrical texture in PVA. The axis of texture coincides with extrusion direction, and hence the PVA molecules in quasi-crystalline fields oriented along extrusion direction. In samples with 10 and 20 wt.% of PHB a well-defined axial texture of PHB crystallites is evident, where the texture axis coincides with direction of extrusion as well. However, the PHB crystallites oriented relative to the texture axes so that the extrusion direction in line with the axis a of elementary crystalline cell. Hence, the axes of PHB molecules are normally oriented relative to extrusion direction. 

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