Subject photovoltaics

Concerning the photovoltaic devices, when subjected to solar emission at AM 1.5, the short-circuit current (Isc) signals were 480,530, and 600 pA for Morus nigra, Morus nigra plus P-carotene and Mix, respectively. This means that the best performances were observed in the case of the blend of all organic derivatives used. 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

The final two chapters deal with applications (in the scientific as well as commercial sense) of CD films. As already mentioned, photovoltaic cells is the one subject that has given CD a push in the last decade, while photoelectrochem-ical cells was probably the main driving force for such studies in the decade before that. Chapter 9 deals with Photovoltaic and Photoelectrochemical Properties. 

Chemical deposition of ZnS has been the subject of considerable activity, the main reason for which is its hoped-for substitution for CdS in thin-film photovoltaic cells. Since the chemistries of Zn and Cd are similar in many ways, it might be expected that deposition of their chalcogenides is also similar. However, there is a dominant difference in their properties that results in the fact that ZnS is considerably more difficult to deposit by CD than CdS. This difference is manifested by the difference in solubility products between the respective hydroxides and chalcogenides. Considering, for example, the sulphides, the relevant values of K p are ... 

Dye-sensitized solar cells (DSSCs) are photoelectrochemical solar devices, currently subject of intense research in the framework of renewable energies as a low-cost photovoltaic device. DSSCs are based upon the sensitization of mesoporous nanocrystalline metal oxide films to visible light by the adsorption of molecular dyes.5"7 Photoinduced electron injection from the sensitizer dye (D) into the metal oxide conduction band initiates charge separation. Subsequently, the injected electrons are transported through the metal oxide film to a transparent electrode, while a redox-active electrolyte, such as I /I , is employed to reduce the dye cation and transport the resulting positive charge to a counter electrode (Fig. 17.4). 

As mentioned earlier, the DSSC is a very attractive and promising device for solar cell applications that has been intensively investigated worldwide, and its photovoltaic mechanism has also intensively investigated [11-20]. Moreover, commercial applications of the DSSC have been under investigation. In this chapter, we describe the DSSC, including its component materials, structure, working mechanism, efficient preparation procedure, current researches, and long-term stabilities. We also introduce the subjects for improvement of its performance and commercial applications. 

Applications of undoped (semiconducting) CPs fill only one line in Table 2. None has reached the market yet, and as for other classes of CPs, several applications that were advocated in the past have failed to meet the necessary requirements. In the early 1980s, for instance, a significant amount of work was invested in the study of CP photovoltaic cells [130], but the subject is no longer active. 

The development of amorphous silicon solar cells has progressed so well in recent years that they threaten to dominate the field of solar energy conversion. It is difficult to see how wet systems can compete with these cells, the only limitations of which arise from design problems. In the near future, it seems probable that their only failure wOl be the material used to support the cells. The progress and status of this subject does not come within the scope of this review and the interested reader should consult journals directed more towards solid-state physics than photochemistry. In this Section, we consider only aspects of photovoltaics that are directly relevant to photochemistry. 

Photovoltaic effects in polymers have continued to attract interest. Polyethylene films sandwiched between parallel transparent electrodes exhibit photocurrent pulses on illumination after being subjected to d.c. fields of up to 105 V mm-1 the effect is attributed to a hopping motion of detrapped electrons in the field of an injected space-charge.156 Similar studies have been carried out on polyethylene terephthalate),157 other organic polymers,168 and polymer- 158 ... 

Thermomechanlcal Behavior. Requirements for optical performance Impose unprecedented requirements for dimensional stability of polymers used In hlgh-concentratlon reflectors. Requirements for mechanical compatibility are also strict for photovoltaic systems subjected to moisture and thermal stresses. Moisture, temperature, and UV, separately and In combination, can change the volume and thus the stress state of polymers. For example, temperature and humidity cycles alone do not cause surface micro-cracks In polycarbonate. However, In the presence of UV radiation, such cycles cause microcracks, while UV alone does not [32]. An understanding of these relationships Is essential to permit reliable design of equipment that uses polymers. 

---