Molecularly doped polymer field

In molecular doped polymers the variance of the disorder potential that follows from a plot of In p versus T 2 is typically 0.1 eV, comprising contributions from the interaction of a charge carrier with induced as well as with permanent dipoles [64-66]. In molecules that suffer a major structural relaxation after removal or addition of an electron, the polaron contribution to the activation energy has to be taken into account in addition to the (temperature-dependent) disorder effect. In the weak-field limit it gives rise to an extra Boltzmann factor in the expression for p(T). More generally, Marcus-type rates may have to be invoked for the elementary jump process [67]. 

Dunlap DH, Parris PE, Kenkre VM (1996) Charge-dipole model for the universal field dependence of mobilities in molecularly doped polymers. Phys Rev Lett 77 542... 

Figure 109 Poole-Frenkel-type plots of the field dependent mobility in a molecular-doped polymer (TAPC PC) at different temperatures. A change from the negative to positive value of [see Eq. (265)] is well pronounced at T > 240 K. After Ref. 479. Copyright 1991 American Institute of Physics.

Figure 169 External quantum efficiency of molecularly doped-polymer-based SL LEDs from Fig. 151 as a function of electric field (a), and recombination-to-transit time ratio for three of them, obtained from Eqs. (315) and (317) with P = Ps = 0.25, = 0.6 and (pT = 11% for LEDs 1,2 and 3, respectively (b). After Ref. 389. Copyright 2001 Institute of Physics (GB), with permission.

A triplet exciton annihilation mechanism has been proposed for charge generation in molecularly doped polymers initiated with very fast, high-intensity, excitation [25b,c]. In this mechanism it is proposed that both charge separation, associated with the Onsager model, and the fusion process are very strongly field-dependent. This model has not been invoked in recent years. 

In molecularly doped polymers and polymers with nlo-active pendant groups the main polymer chain has a saturated chemical structure, which does not contribute significantly to the overall nlo properties. As noted earlier, it is necessary to induce polar order in such systems to obtain finite values of This is usually achieved by the application of an electric field while the polymer is heated above its glass transition temperature (Tg). This produces a partial ordering of the polar additive or pendent group. This order is then frozen in by cooling the polymer below Tg. For such poled films there are a limited number of finite, unequal components of the tensor The symmetry of such films is 00 mm, i.e. an infinite-fold rotation symmetry about the poling direction. The non-zero coefficients of the tensor are... 

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