Gaussianly Distributed Traps

Here is the hole trap density, g is the degeneracy factor (taken as unity in the calculations), Etp is the ionization energy of the hole traps, Ev is the valence band edge (i.e. HOMO), Ny is the effective density of states for holes, at is the standard deviation of the Gaussian distribution of traps, and the factor expOS /F/fcr) arises due to the Poole-Frenkel effect. Analytical solution of (3.58) and (3.60) can not be obtained. Numerically computed results are shown in Fig. 3.29. 

In studies of low-mobility insulators, two types of continuous trap distributions are commonly used the exponential distribution of traps [364] and the Gaussian distribution of traps [365]. 

In principle the situation seems to be similar for energetically distributed traps with Gaussian or exponential density of states. But especially in the case of an exponential trap density of states in the gap with the maximum at a distance Eq above the valence band edge... 

Reversible energy transfer between monomeric and dimeric forms of rhoda-mine 6G in ethylene glycol has been observed" and the concentration dependence of the overall fluorescence quantum yield has been modelled by Monte-Carlo simulations. Triplet energy transfer in disordered polymers has been analyzed on the basis of Bassler s model in which the trap energies have a Gaussian distribution." Energy transfer has also been observed in mono-layers and for photoswitchable molecular triads." The structural requirements for efficient energy transfer from a carotenoid to chlorophyll have been... 

Fig. 8.28 Experimental values and a simulation out using a Gaussian distribution of traps with (solid lines) of the temperature-dependent j(V) a density A/t = 9 lo ...

Electrons in PPV The electron current in PPV is smaller than the hole current (Fig. 8.57). Its strong field dependence is typical of a trap dominated space-charge-limited current with an energy distribution of the traps. The experimental values of the characteristics (Fig. 8.57) obey Eq. (8.96) or (8.98) with a distribution parameter i = Et/kT for an exponential or m for a Gaussian distribution. The fit to the measurements shown in Fig. 8.57 yields the value Et/k = 1500 K, that is Et = 130 meV [56], [57], and thus again a value of the order of 100 me V. 

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