Injection of charge carriers

A light-emitting diode (LED) is a forward-biasedp—n junction in which the appHed bias enables the recombination of electrons and holes at the junction, resulting in the emission of photons. This type of light emission resulting from the injection of charged carriers is referred to as electroluminescence. A direct band gap semiconductor is optimal for efficient light emission and thus the majority of the compound semiconductors are potential candidates for efficient LEDs. 

In many cases, local details are not important and an overall balance of generation and recombination, of extraction and injection of charge carriers gives the correct results for electrical and energy currents originating from a solar cell, as we know from extensive experience. 

The hole mobility /u-h in OCiCio-PPV is 5 x 10-11 m2/V s. The electron mobility /xe in PCBM is 2 x 10-7 m2/V s. However, the transport of separate charge carriers in an interpenetrating network may be different than the transport in the individual compounds. In Ref. [65] the transport and injection of charge carriers in OCiCio-PPV PCBM bulk-heterojunction diodes are investigated. 

These observations along with the independence of the EL spikes on the applied voltage polarity13 suggests that the EL spikes appearance can not be directly related to regular injection of charge carriers from the electrodes and their transport across the device, as it is in the case of stationary EL. 

An important issue for the performance of an organic electronic device like an OFET is the injection of charge carriers, electrons or holes, from the electrode into the organic material. In case of the commonly used metal electrodes an efficient electron injection is possible only if the Fermi level of the metal and the energy of the lowest unoccupied molecular orbital (LUMO) of the organic material differs by a small amount only. A similar statement applies for hole injection, in this case the position of the highest occupied molecular orbital (HOMO) has to match with the position of the Fermi level. When noble metals, in particular Au, are being used for an electrode one may naively assume... 

Stationary dark currents in disordered thin films which contain no intrinsic charge carriers require the injection of charge carriers. If Ohmic contacts have been prepared, then the stationary dark current is not limited by the contact resistance, but instead by the mobility and the injected space charge. Since about 1985, stationary dark currents through disordered thin films have attracted great interest, especially since at that time, suitable contacting methods were developed to permit injection of both electrons from the one electrode as well as holes from the other. This made... 

With a DC field, there may be injection of charge carriers at the solid-liquid interface but its role in the electrohydrodynamics of the nematic phase is not yet fully understood. However, as remarked earlier, a frequency of about 10 Hz is enough to suppress charge injection. We shall therefore neglect it in the present discussion. 

Variations in Vbi will therefore have a profound effect on the current density vs. voltage (/-V) and EL (electroluminance) characteristics of the devices since <1>b controls injection of charged carriers. 

The process of charge carrier transport may occur in two steps (1) the injection of charge carriers into the material and (2) the movement of charge carriers through the material via hopping, tunneling, ballistic transport, diffusion, or metallic conduction. For composites with at least two phases, several aspects have to be considered the conduction in the polymer matrix, in the filler material, between adjacent filler... 

Measurement of the temporal variation of the conductivity after or during injection of charge carriers yields information on the transport properties of the charge carriers involved. 

The injection of charge carriers leads to bulk liquid motion. This effect is also known as electrohydrodynamic motion (EHD). From measurements of the liquid velocity and from calculations of the flow by means of the Navier-Stokes equations it was found that also in the presence of liquid flow. Equation 71 for the SCL currents remains valid (Takashima et al., 1988). The mobility obtained from the slope, however, is the hydrodynamic mobility. For the electrode arrangement — razor blade/plane electrode — the injection current depends on the applied voltage as. 

The injection of charge carriers in nonpolar liquids under the influence of a high electric field strength gives rise to a number of effects which may have some technological importance. 

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