Charge carriers mobility

Data reproduced from the references cited, with permission from the Japan Society of Appiied Physics, Institute of Pure and Applied Physics, and Elsevier. 

One issue with rr-PHT is its low on/off ratio when exposed to air, which is attributed to its low ionization potential (IP 4.8 eV). Although high on/off ratios can be obtained under inert conditions or after dedoping the polymer film under vacuum, on/off ratios quickly decrease when the polymer is exposed to ambient air. Both water and oxygen are responsible for the lower on/off ratio, moisture being the dominant factor [223]. High on/off ratios and good stability can be obtained if rr-PHT is kept under an inert atmosphere [205, 224]. 

PAT = regioregular poly(3-alkylthiophene) PEG = poly(ethylene glycol) ATRP = atom transfer radical polymerization 

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The hyperbolic relaxation equation (A-5-2.4.1 a) contains charge carrier mobility as a variable, which should be sensitive to oil viscosity. This is found to be the case for some viscous nonconductive liquids. These have much slower rates of charge dissipation equivalent to an Ohmic liquid whose conductivity is 0.02 pS/m (5-2.5.4). 

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

In the above consideration it has been tacitly assumed that the charge carrier mobility docs not depend on the electric field. This is a good approximation for molecular crystals yet not for disordered systems in which transport occurs via hopping. Abkowitz et al. [37] have solved that problem for a field dependence of ft of the form p-po (FIFU) and trap-free SCL conduction. Their treatment predicts... 

Figure 12-16. Field dependence of die charge carrier mobility in an undiluted hopping system al various values of the disorder parameter a = a/kT (Kef. [67]).

Figure 3. (a) Representation of the hexagonal discotic mesophase formed by hexadodecyl substituted HBC 33. (b) The temperature dependence of the intracolumnar charge carrier mobilities for 33 and 34. Phase transition tempera-... 

S.H. Lee, T. Yasuda, and T. Tsutsui, Charge carrier mobility in blue-green emitting fluorenyl-substituted polyfp-phenylene vinylene)s, J. Appl. Phys., 95 3825-3827, 2004. 

WAXD, DSC, and vibrational studies on //-hexyl-substituted polysilanes with 5%, 33%, or 67% /z-hexylsilyne branching points showed that the introduction of branching partially reduced the high-crystallinity characteristic of PDHS.365 It was also found that the charge carrier mobilities decreased with increasing branching points, and... 

All of the above-mentioned active materials show a crystal structure characterized by a continuous network of corner shared octahedral units of metal cations (TaC>6, NbOg, Ti06), which presumably allows for high charge carriers mobilities and efficient charge separation. A relevant role of local electric dipole moments cannot be excluded [111] (see also below). 

It should also be briefly recalled that semiconductors can be added to nanocarbons in different ways, such as using sol-gel, hydrothermal, solvothermal and other methods (see Chapter 5). These procedures lead to different sizes and shapes in semiconductor particles resulting in different types of nanocarbon-semiconductor interactions which may significantly influence the electron-transfer charge carrier mobility, and interface states. The latter play a relevant role in introducing radiative paths (carrier-trapped-centers and electron-hole recombination centers), but also in strain-induced band gap modification [72]. These are aspects scarcely studied, particularly in relation to nanocarbon-semiconductor (Ti02) hybrids, but which are a critical element for their rational design. 

A key feature of our polyphenylene dendrimers is that they can be planarized and thus reduced in dimensionality by intramolecular dehydrogenation [29,35]. This results in large, fused polycyclic aromatic hydrocarbons (PAHs). PAHs serve as structurally distinct, two-dimensional subunits of graphite and show attractive properties such as high charge carrier mobility, liquid crystallinity, and a high thermal stability, which qualifies these materials as vectorial charge transport layers [81]. 

As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift. The charge-carrier mobility of different EHO-OPPE-Pt samples was determined by TOE measurements as described above for the neat EHO-OPPE. The shape of the photocurrent transients of all EHO-OPPE-Pt samples was similar to those shown in Figs. 6 and 7 for the neat EHO-OPPE. This indicates that these organometallic conjugated polymers networks are also characterized... 

These different modes of transport result in a dissimilar temperature dependence of the charge carrier mobility, and this often provides a convenient means to investigate which transport regime may apply. In this chapter, due attention is therefore given to experimental approaches that allow for an investigation of the transport mechanism, and concomitantly of the underlying electronic structure. 

Monte Carlo simulations [54], analytical effective medium theory [64], and stochastic hopping theory [46] predict a dependence of the charge carrier mobility as a function of temperature and electric field given in (3) ... 

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