Charge transport traps

It is obvious, and verified by experiment [73], that above a critical trap concentration the mobility increases with concentration. This is due to the onset of intertrap transfer that alleviates thermal detrapping of a carrier as a necessary step for charge transport. The simulation results presented in Figure 12-22 are in accord with this notion. The data for p(c) at ,=0.195 eV, i.e. EJa—T), pass through a minimum at a trap concentration c—10. Location of the minimum on a concentration scale depends, of course, on , since the competition between thermal detrapping and inter-trap transport scales exponentially with ,. The field dependence of the mobility in a trap containing system characterized by an effective width aeff is similar to that of a trap-free system with the same width of the DOS. 

A T)n sequence. In double strand 21 (Scheme 5) the charge is trapped by a GGG triplet, and it turned out that the hole transport over 8 A T base pairs is nearly as efficient as the hole transport over 2 A T base pairs. 

In the perfectly paired double strand 22, the yield of product PGgg> which indicates the amount of charge that has reached the hole trap GGG, is 68%. But if the intermediate G C base pair is exchanged by a G T mismatch, the efficiency of the charge transport drops to 23%. With an abasic site (H) opposite to G the hole transport nearly stops at this mismatched site (Fig. 15). We have explained this influence of a mismatch on the efficiency of the charge transport by a proton transfer from the guanine radical cation (G2 +)... 

Important electrical informations about OLEDs, such as charge transport, charge injection, carrier mobility, etc., can be obtained from bias-dependent impedance spectroscopy, which in turn provides insight into the operating mechanisms of the OLED [14,15,73,75 78]. Campbell et al. reported electrical measurements of a PLED with a 50-nm-thick emissive layer [75], Marai et al. studied electrical measurement of capacitance-voltage and impedance frequency of ITO/l,4-Mv-(9-anthrylvinyl)-benzene/Al OLED under different bias voltage conditions [76], They found that the current is space-charge limited with traps and the conductivity exhibits power-law frequency dependence. 

The results taken as a whole reveal the existence of at least three different trap species in the band gap of Sb(As)j Sei noncrystaUine semiconductors. These species are located at energies 0.22, 0.34, and 0.45 eV, respectively, below the conduction band edge and control the electron transport properties of the material. It seemed that Sb and As introduce a new set of detectable charge-carrier traps. 

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