Space charge limited current experiments

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...

The conditions of the experiment discussed here are different than the restrictions imposed to obtain the Mott-Gurney equation. However, at least qualitatively, Equation 8.38 can describe the space charge-limited current effect. To test this hypothesis, Equation 8.38 was experimentally tested, and it was shown that it is approximately satisfied (see Figures 8.13 and 8.14) [112]. 

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. 

In 2014, Li, Hou, and co-workers synthesized a hydrazide polymer that mimics the ion transport of Gramicidin A. ° This polymer carried phenylalanine side chains, which allowed the polymer to be inserted into a lipid bilayer at low concentrations. Patch clamp experiments showed that this polymer could transport some alkali-metal ions such as Na , K , and also NH4 across the membrane. Patch-current traces up to 15 s showed that the structure was stable within the bilayer. As the NH4 selectivity was higher than that for K, the inner pore was estimated to be smaller than 1 nm. Another field where helical polymers have been used is the Space-Charge-Limited Current (SCLC) hole mobility. In 2015, a discotic polycyclic aromatic... 

Their existence in ultrapure organic crystals has been verified beyond a doubt (cf for example Fig. 8.27). Particularly in thin crystals such as those used in transistors (see Chap. 12), the currents are space-charge limited for the determination of mobilities, they are however seldom as reliable as TOF experiments using the photoconductivity, due to contact problems between the metal electrodes and the organic crystals. 

The polymerfilm was sdution coated onto a carbon loaded pdymer film substrate (MystR ) and then overcoated with an evaporated semi-transparent /d top contact Tlie darit current transient injection experiment is carried out by apidying the positive voltage step to the substrate contact and time resolving the transient response of the injected hde current The early time dark injection current is depicted in the insert and the time at which the maximum current occurs is denoted as t. According to the theory of transient space charge limited injection, the time tp can be rdated to the moUlity p of injected ludes from equation 3,... 

Three concentrations of each redox couple that ranged over two orders of magnitude were examined as well as a solution containing only electrolyte. The details of these comprehensive experiments will be published elsewhere (22.) however, several pertinent features are described here. The kinetic currents were measured at constant potential. In order to eliminate mass transfer limitations to the current, a jet electrode configuration was utilized (42). The capacitance of the space charge layer (Csc) was measured at the same potentials simultaneously with the kinetic currents. 

Mass accuracy is usually the most important parameter as it defines the most important data within an experiment. Mass accuracy is usually presented as parts per million (ppm) for example, 20 ppm means that the real mass of an ion measured to 1000 Da has a predicted error margin of 20mDa. While it is not usually specified, the best way to define this error is at 2 standard deviations in the errors on the calibration, which means that a measured mass is -95% likely to be within that range. It is not critically important how this expected error is defined, provided that it is clearly stated exactly how it is calculated. Mass accuracy is limited by the quality of the calibration (how accurate it was to start with, how much it drifts with time, how much space charge has shifted the current spectrum relative to the instrument calibration, etc.), and by how accurately the center of the peak can be determined (which is determined by the number of points on a peak and how accurately the peak follows a theoretical peak shape). 

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