Space-charge-limited current SCLC

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 ... 

As soon as the concentration of free carriers (n ) injected from Ohmic contacts exceeds the concentration of carriers (no) produced by intrinsic or extrinsic excitation, space-charge-limited currents (SCLC) appear. In this case the Ohmic current... 

Steady-state space charge limited currents (SCLC) have been applied to study traps in organic solids since the early 1960 s (Mark and Helfrich, 1962 Thomas et al., 1968 Reucroft and Mullins, 1974). Superquadratic dependences of the currents upon voltage, J azVn where n > 2, have been interpreted assuming the presence of traps exponentially distributed over a wide energy range. This may be expressed by (20), where h(e) is the density of states per... 

Estimated from the trap-free space charge limited current (SCLC) method... 

Unambiguous steady-state measurements are carried out only in the trap-free space-charge-limited-current (SCLC) regime (23), when the average transit time (f j of any excess injected carrier across the sample bulk is shorter than the time required for the bulk to locally neutralize the carrier (22). The transit time ( r) has been defined in equation 1. The time to neutralize any excess injected carrier is the bulk dielectric relaxation time, Tr ( r = in which p is the bulk resistivity and e is the bulk dielectric... 

The observation of space charge limited currents (SCLC) in nanoscaled pure and chromium-doped titania was reported [310] and both the free-charge carrier density and the trapped-charge carrier density were given. 

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. 

The IV behaviour is described with a formation of a space charge upon the dominant electron-injection (space charge limited currents, SCLC). The current density follows a power law dependence, described with the Mott-Goumier formula in (1)... 

In this section, after a brief introduction of the OFET operation principles, we outline the main signatures of the intrinsic polaronic transport observed in the experiments with single-crystal OFETs. We compare them to the results of TOF and space-charge limited current (SCLC) experiments that probe charge transport in the bulk. 

Space-charge limited currents (SCLC) also lead to a field independence of the slope of Arrhenius (/ vis. /T) plots. Both behaviours are generally found (but see below) for not intentionally doped and therefore p-type oligothiophenes contacted by noble metals like Au (for the influence of the contact material see Section 6.1) [233,258,259]. The transition from the linear to the quadratic dependence of the I/V curve is often found around 1 V [258,259]. 

This simple but important equation is called Child s law and was originally derived for vacuum electron valves. The current which is flowing through the insulator (or through the vacuum) is termed the space-charge-limited current (SCLC) and will be treated in more detail in Sect. 8.4.4. It is proportional to the square of the voltage V and inversely proportional to the third power of the sample thickness d and therefore experimentally clearly distinguishable from an Ohmic current, which is proportional to V/d. 

The carrier mobility in the mixed CuPcC o films has been obtained by modeling the current density-voltage (j-V) characteristics for hole- and electron-only devices using the space-charge-limited current (SCLC) theory (Pope and Swenberg, 1999 Rand et al., 2005), viz. ... 

Space charge limited current (SCLC), 16-9, 16-19, 19-3 Spectral degradation, 5-22, 5-25-5-27 Spin density wave (SDW), 16-12, 16-14 Spiral morphology, 3-3, 3-7-3-S, 3-10-3-12 Spiro linkages, 5-6, 5-20, 5-22, 5-23, 5-24 Spiro-type oligoarylenes, 5-23, 5-24, 5-30 STABASE, 9-21... 

Dark conductivities ap allow a number of conclusions [199, 200] and are thus measured first. Since Iq = a U a linear dependence (s 1) of the dark current Id on the voltage U indicates ohmic behavior, a superlinear dependence (s 2) the presence of space charge limited currents (SCLC). The constant a is directly proportional to the proportion of free to trapped charge carriers, the dielectrical constant of the sample, the electrical field constant and the mobihty of the charge carriers. Finally a is also determined by the cell geometry. As a is proportional to the mobility p of the charge carriers it is in certain cases possible to calculate p from the slope of the Id/U curve. The dark conductivity of an ohmic conductor varies with the temperature in an Arrhenius type fashion. The... 

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