Hole mobility evolution

FIGURE 1.1.8 Evolution of the hole mobility as a function of the magnitude of the electric field in a one-dimensional array of pentacene molecules separated by 4 A. 

Fig. 12 Evolution of P3HT nanofibril width Hafm and hole mobility fi as function of weight-average molecular weight and weight-average contour length L [79]. Thin films were prepared by drop-casting from toluene (1 mg/mL). (Reprinted with permission from Zhang et al. [79]. Copyright (2006) American Chemical Society)...

Here, the responses are normalized to the maximum concentration r>o of excitations. The signal evolution in a bi-exponential decay is therefore n(t) = Ani(t) + Bn2(t), where A and B are proportional to the radiative (or non-radiative) rates of the two levels. For solids, a monoexponential PL decay can be explained by the thermally activated recombination of highly mobile electrons and holes trapped onto radiative defects. Such a mechanism requires that the spatial separation of the trapped charge carriers be small. 

The electrons and holes generated by impact ionization drift in opposite directions. This generates a dipole field which counteracts the external field. Since y is a very steep function of F the self-fields have a regulation effect on the field distribution. Whenever F > F, then rapid impact ionization sets in which reduces the field. Since an avalanche never represents a stationary solution, the net result is not F = F, as in the threshold mobility situation (Hibma and Zeller, 1986). In practice, numerical simulation models have to be used to describe the evolution of an avalanche until destruction of a solid or liquid dielectric. 

Fig. 2 The evolution of the hole field-effect mobility of various organic semiconductors in time. The data of Table 1 are grouped into families of molecules with similar main chain. Additionally, hole field-effect mobilities of rubrene and pentacene in single crystals are depicted. For comparison, the electron mobilities of a-Si H and poly-Si are shown...

Fig. 8 The evolution of the electron and hole field-effect mobility of pentacene in time. For comparison, the electron mobility of a-Si H is shown. The data are listed in Table 2...

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