Hole drift mobility field dependence

Fig. 5. Field dependence of hole drift mobilities for a range of TNF PVK molar ratios. Data taken at T = 24 °C17 ...

Fig. 3.13. Temperature dependence of the (a) electron and (b) hole drift mobility at different applied fields ranging from 5 x 10 V cm" to 5 X 10 V cm". The field dependence of is caused by the dispersion (Marshall et al. 1986, Nebel et al. 1989).

Strong Field Dependence of Drift Mobility. Hole drift mobility increases sharply with field, and with PVK, a characteristic E dependence of log (X is exhibited, as originally reported by Pai (36), whose data are displayed in Figure 5. Drift mobility values are low and fall into the range cm /V-s at room temperature. 

Strong Temperature Dependence of Drift Mobility. Figure 6 is an Arrhenius representation of hole drift mobility data on a 0.2 1 TNF-PVK film (iO). The apparent activation in this representation is field dependent,... 

Numerous studies of charge transport in amorphous molecular materials have shown that hole drift mobilities of amorphous molecular materials vary widely from 10 6 to 10 2 cm2 NT1 s 1 at an electric field of 1.0 X 105 V cm-1 at room temperature, greatly depending upon their molecular structures. Table 7.6 lists hole drift mobilities of some amorphous molecular materials that function as holetransporting materials in OLEDs. 

Fig. 3. Field dependence of the hole-drift mobilities in PDS(Th)4 at room temperature.

By using higher injection levels and the theories (Many and Rakavy (1962) Helfrich and Mark (1962)) which take account of the resulting space charges, Rossiter and Warfield (1971) were able to extend the drift velocity measurements to 78 K. As shown in Table 5.4 the observed activation energy for holes is 0.095 eV, considerably smaller than those of other workers. They find, moreover, a break in the T-dependence of for holes at 150 K. Below this temperature the activation energy is only 0.0093 eV. In addition, they report a small field dependence of the hole drift mobility for fields in excess of 10 V/cm. This had not been seen by the earlier groups. 

It was established that the elevated hole drift mobility of DCZB polymers is due to the reduced concentration of trapping sites which are in fact excimer-forming sites. This was confirmed by the temperature and electric field dependencies of the hole mobility. These observations support the idea that eharge transport and exciton transport have... 

The electric field dependence of the hole mobility in a series of PVK TNF films of varying composition is shown in Fig. 5(b)17. The carrier drift mobilities are extremely low and strongly dependent on the electric field. Similar electric field dependence was observed for electron drift mobilities. The mobilities obey the empirical relation... 

The drift mobility in this dispersive regime has an unusual electric field and thickness dependence. Fig. 3.13 shows the field dependence of the electron and hole mobility at different temperatures (Marshall et al. 1986, Nebel, Bauer, Gom and Lechner 1989). The electron drift... 

Mycielski and Lipinski (1978), Kania et al. (1979), Mycielski et al. (1983), and Bak et al. (1995) reported electron and hole mobilities of vapor-deposited polyciystalline layers of various hydrocarbons CuPc, coronene, / -terphenyl, p-quaterphenyl, and tetracene. The mobilities were in the range of 10-3 to 10 5 cm2/Vs and inversely proportional to the field. A mobility with an E-l field dependence is equivalent to a field-independent drift velocity. 

In the simplest embodiment of the time-of-flight experiment, electron-hole pairs are injected at one face of a dielectric material at i = 0 with a short flash of strongly absorbed light. The electrons (or holes depending on the sign of the applied field) are drawn across the material by an externally applied field, as shown in Fig. 1. The two-dimensional sheet of electrons, in the plane perpendicular to the plane of the figure, drifts across the sample with velocity I d = where is the drift mobility and F the applied field. For a fixed... 

Because both carriers, electrons and holes, can be mobile in a-Si H, blocking contacts for both electrodes are needed to prevent carrier injection from the electrodes. In this case the photocurrent is a primary current that saturates with unity collection efficiency when ptxE > d, where n is the mobility of the photocarriers that drift in a-Si H, r the lifetime of photocarriers, E is the electric field in a-Si H, and d the thickness of a-Si H. In the saturation photocurrent region, the photocurrent is not very dependent on a-Si H film quality and increases linearly with increasing light intensity. 

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