Solid holes

For the QD-sensitised cell, QDs are substituted for the dye molecules, as shown in Fig. 3.19b they can be adsorbed from a colloidal QD solution (Zaban et al, 1998) or produced in situ (Weller, 1991 Liu and Kamat, 1993 Vogel et al, 1994 Hoyer and Konenkamp, 1995). Successful PV effects in such cells have been reported for several semiconductor QDs including InP, CdSe, CdS, PbS and InAs (Weller, 1991 Liu and Kamat, 1993 Vogel et al, 1994 Hoyer and Konenkamp, 1995 Zaban et al, 1998 Nozik, 2001a Robel et al, 2006 Yu et al, 2006 Tachibana et al, 2007). Possible advantages of QDs over dye molecules are the tunability of optical properties with size, better heterojunction formation with solid hole conductors, and the unique potential capability of the QD-sensitised solar cell to produce quantum yields greater than one by MEG (inverse Auger effect) (Nozik, 2002). 

Nanocrystals of wide bandgap p-type semiconductors from CuA102 and 6-CuSCN have been synthesized [209], Both types of nanocrystals were dispersed in PVK in dichloromethane solution. In this way, a nanocrystals embedded polymeric matrix was formed. The solution was finally cast by dip-coating. These materials were investigated as solid hole-transporters in dye-sensitized solar cells. 

Prakash T, Ramasamy S. Dye sensitized solar cells using nanocrystalline cual02/y6-cuSCN embedded poly(vi-nyl carbazole) composites as solid hole-transporter. Sci Adv Mater 2012 4(l) 29-34. 

Although the most commonly used redox couple to act as a hole transport medium is the I3 /I this does not mean the couple is necessarily unique. Actually the space for improvement for DSSCs that use this redox mediator is mostly limited to improvements in better light harvesting dyes [41]. Corrosion, light absorption and diffusion limitations had been identified for the l3 /I pair and it has been replaced successfully by cobalt-based redox systems [14], as well as by organic hole conductors [42]. Difficulties in sealing to prevent evaporation and water diffusion into the cell led to research into the substitution of liquid redox pair electrolyte, replacing the liquid for solid or quasi-solid hole-conduction media, such as polymeric, gel [43], or solid electrolytes [44]. 

Solid-state redox mediators or hole conductor materials would make it possible to construct completely solid-state DSSCs that will probably have considerable added commercial value. One of the main difficulties in substituting liquid electrolytes is the need for an interpenetration of the sensitised metal oxide by the electrolyte, in order to have efficient contact between the sensitiser cation (the hole) and the mediator. Additionally, prospective solid hole collectors should have the following properties the valence band of the hole collector material must be located above the bottom of the sensitiser dye ground state it must be transparent throughout the visible spectrum, where the dye absorbs fight and the deposition of the solid material should be done without degrading the monolayer of sensitiser dye adsorbed on Ti02. 

Permeable intervals can be identified from a number of logging tool measurements, the most basic of which is the caliper tool. The caliper tool is used to measure the borehole diameter which, in a gauge hole, is a function of the bit size and the mudcake thickness. Mudcake will only build up across permeable sections of the borehole where mud filtrate has invaded the formation and mud solids (which are too big to enter the formation pore system) plate out on the borehole wall. Therefore the presence of mudcake implies permeability. 

Dislocation theory as a portion of the subject of solid-state physics is somewhat beyond the scope of this book, but it is desirable to examine the subject briefly in terms of its implications in surface chemistry. Perhaps the most elementary type of defect is that of an extra or interstitial atom—Frenkel defect [110]—or a missing atom or vacancy—Schottky defect [111]. Such point defects play an important role in the treatment of diffusion and electrical conductivities in solids and the solubility of a salt in the host lattice of another or different valence type [112]. Point defects have a thermodynamic basis for their existence in terms of the energy and entropy of their formation, the situation is similar to the formation of isolated holes and erratic atoms on a surface. Dislocations, on the other hand, may be viewed as an organized concentration of point defects they are lattice defects and play an important role in the mechanism of the plastic deformation of solids. Lattice defects or dislocations are not thermodynamic in the sense of the point defects their formation is intimately connected with the mechanism of nucleation and crystal growth (see Section IX-4), and they constitute an important source of surface imperfection. 

A special case of adsorption in cavities is that of clatherate compounds. Here, cages are present, but without access windows, so for adsorption to occur the solid usually must be crystallized in the presence of the adsorbate. Thus quinol crystallizes in such a manner that holes several angstroms in diameter occur and, if crystallization takes place in the presence of solvent or gas... 

Zilker S J, Kador L, Friebel J, Vainer Y G, Kol chenko M A and Personov R I 1998 Comparison of photon echo, hole burning, and single molecule spectroscopy data on low-temperature dynamics of organic amorphous solids J. Phys. Chem 109 6780-90... 

In solid state materials, single-step electron transport between dopant species is well known. For example, electron-hole recombination accounts for luminescence in some materials [H]. Multistep hopping is also well known. Models for single and multistep transport are enjoying renewed interest in tlie context of DNA electron transfer [12, 13, 14 and 15]. Indeed, tliere are strong links between tire ET literature and tire literature of hopping conductivity in polymers [16]. 

Another method, which is especiafly suitable for low melting point solids or solids which decompose at low temperatures, is to place the material on a porous plate or pad of drying paper, and to cover the latter with another sheet of Alter paper perforated with a number of holes or with a large clock glass or sheet of glass supported upon corks. The air drying is continued until the solvent has been completely eliminated. 

This procedure is used to separate crystallized product from solvent or to remove crap and solids from a liquid. Figure 8 shows the proper apparatus to use. The collecting flask is called a side arm flask and to that extended nipple (tee heel) is attached a vacuum source. The thing that is shoved through the rubber stopper is called a Buchner funnel and is usually made of white porcelain or, preferably, PP. The Buchner funnel, when viewed from above, can be seen to have lots of pin holes in the bottom surface of its reservoir. Over this surface is layered a single sheet of rounded filter paper or paper towel. 

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