Mobility space-charge-limited current

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

One result of the field-dependent mobility is that the space charge-limited current (SCLC, the maximum current that can How in the bulk of the sample) does no longer follow a simple V2H scaling [132] on the voltage Land sample thickness L. Muigatroyd [133] was able to show that, for a mobility as in Eq. (13.4), the monopolar SCLC current could be well approximated by ... 

Fig. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 4.1). From [90] with permission. Copyright (2008) by the American Institute of Physics...

Fig. 13 Experimental (symbols) and theoretical (lines) data for the current-density as a function of applied voltage for a polymer film of a derivative of PPV under the condition of space-charge-limited current flow. Full curves are the solution of a transport equation that includes DOS filling (see text), dashed lines show the prediction of Child s law for space-charge-limited current flow assuming a constant charge carrier mobility. From [96] with permission. Copyright (2005) by the American Institute of Physics...

Young RH (1994) Trap-free space-charge-limited current - analytical solution for an arbitrary mobility law. Phil Mag Lett 70 331... 

The field-dependent mobility, would obviously modify the shape of the field characteristics of space-charge-limited currents [cf. Sec. 4.3.1 Eqs. (168), (175), (176) and (185) the first original work see Ref. 377]. For example, the Schottky-type... 

It is interesting to compare these values with the result of another method, the analysis of current-voltage relation for space-charge-limited currents. Such a study on a-sexithienyl [229] has given an effective mobility p, 2 x 10 2 cm2/V s, limited by traps 0.28 eV above the top of the valence band. Thus the trap-free microscopic mobility is likely to be at least two orders of magnitude larger, a typical value for a molecular crystal. 

The trap-free space-charge-limited current (TFSCLC) (22) is proportional to mobility, as shown by equation 5 ... 

The behavior of such a system is easy to predict in the absence of mobile ions. Ohmic contacts and a high resistivity bulk give rise to a bulk-controlled or space-charge limited currents (L3). A complete analysis of the space-charge limited transient current in insulating crystals has been given (14)- The analysis in polymers is modified by the presence of mobile ionic impurities in two ways. First, in thermal equilibrium the bulk ion and electron concentrations must be... 

Accordingly, in this contribution we will address the transport properties of selected materials, tetracene, diindeno[l,2,3-cd l, 2, 3 -lm]perylene (DIP), etc. (see Figure 25.1), which show different chemical stabilities and susceptibilities on (photo-)oxidation due to their respective aromaticity [11]. The temperature dependent charge carrier mobility proves to be an indicator of high sensitivity for chemical and structural irregularities and can be accessed by injection-free Time-Of-Flight (TOF) and injection-based Field-Effect Transistor (FET) and Space-Charge-Limited-Current (SCLC) studies. 

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