These studies support the model of thermally activated injection into a Gaussian DOS distribution of hopping sites and confirm the notion that disorder facilitates injection because it lowers the injection barrier, although the transport velocity decreases with increasing disorder. An analysis of experimental data yields consistent values for the width of the DOS distribution as well as for inter- site separation. compared injection limited currents and space-charge-limited currents in a copper-phthalocyanine sandwich cell with TTO and Al electrodes. Copyright (2005) by the American Institute of Physics.Ī textbook example for the successful application of the model of Arkhipov et al.
Gistpal limited charge full#
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. 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.
Based upon stationary space-charge-limited current measurement, where the charge carriers are in quasi equilibrium so that dispersion effects are absent, the authors determine a width a of the DOS for holes as large as 130 meV with negligible polaron contribution. This is supported by a strictly linear In p cx dependence covering a dynamic range of 15 decades with a temperature range from 150 to 315 K (Fig. conclude that in polyfluorene copolymers hole transport is entirely dominated by disorder. In fact, in their recent work, Mensfoort et al. Copyright (2008) by the American Institute of Physics. The data are inferred from space-charge-limited current experiments and analyzed in terms of the extended Gaussian disorder model (see Sect. 8 Temperature dependence of the zero field hole mobility in the low carrier density limit in a polyfluorene copolymer. Woo, Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injection contacts, Appl. (13.4), the monopolar SCLC current could be well approximated by. Muigatroyd was able to show that, for a mobility as in Eq. 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 on the voltage Land sample thickness L. A summary of the results for the hole mobility of PPV and PPV- related polymers is given in Table 11-1. 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. The charge density and potential are then given by
In 1940, Mott and Gurney derived an exact solution in the particular case where 7 = 0, for a semi infinite material, and assuming that the electric field is zero at X = 00. This second order differential equation cannot be analytically solved in the general case. The electric field created by the injected charges generates a current density J, which is the sum of a drift and a diffusion current
Gistpal limited charge free#
The resulting carrier profile can be calculated from Maxwell s equations, the more pertinent of which is Poisson s equation Į is the dielectric constant of the insulator, and o the permittivity of free space.
When charges diffuse into an insulating material, they give rise to an electrostatic field that acts against the penetration of additional charges into the material. Space-charge limited current (SCLC) occurs in materials with very low concentrations of free carriers (ideally, perfect insulators).
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