Charge carrier injection

The metallic electrode materials are characterized by their Fermi levels. The position of the Fermi level relative to the eneigetic levels of the organic layer determines the potential barrier for charge carrier injection. The workfunction of most metal electrodes relative to vacuum are tabulated [103]. However, this nominal value will usually strongly differ from the effective workfunction in the device due to interactions of the metallic- with the organic material, which can be of physical or chemical nature [104-106]. Therefore, to calculate the potential barrier height at the interface, the effective work function of the metal and the effective ionization potential and electron affinity of the organic material at the interface have to be measured [55, 107],... 

In electroluminescence devices (LEDs) ionized traps form space charges, which govern the charge carrier injection from metal electrodes into the active material [21]. The same states that trap charge carriers may also act as a recombination center for the non-radiative decay of excitons. Therefore, the luminescence efficiency as well as charge earner transport in LEDs are influenced by traps. Both factors determine the quantum efficiency of LEDs. 

In the following section an overview, of several models describing the charge carrier injection and transport of LEDs based on polymers and organic materials, is presented. The focus will be set on mctal/polymer (organic material)/nictal contacts based on a polymer with a low defect concentration will be discussed. A description of LEDs, based on iolymers with a high defect concentration e-m U>... 

Blom et al. [85] stated that the l/V characteristics in LEDs based on ITO/di-alkoxy-PPVs/Ca are determined by the bulk conductivity and not by the charge carrier injection, which is attributed to the low barrier heights at the interface ITO/PPV and PPV/Ca. They observed that the current flow in so called hole-only devices [80], where the work function of electrodes are close to the valence band of the polymer, with 1TO and Au as the electrodes, depends quadratically on the voltage in a logl/logV plot and can be described with following equation, which is characteristic for a space-charge-limitcd current (SCL) flow (s. Fig. 9-26) ... 

Charle, K. P. Spin-Dependent Kinetics in Dye-Sensitized Charge-Carrier Injection into Organic Crystal Electrodes 19... 

Charge-Carrier Injection into Organic Crystal Electrodes... 

The photocurrent is cathodic or anodic depending on the sign of the minority charge carriers injected from the semiconductor electrode into the electrolyte, i.e. the n-semiconductor electrode behaves as a photoanode and... 

No charge injection Minimum bias for charge Carriers injected... 

The existence of two types of mobile charge carriers in semiconductors enables us to distinguish between a majority charge carrier transferred from the electrode into the electrolyte and a minority charge carrier injected from the electrolyte into the electrode. Minority carrier injection causes significant reverse currents, but may also contribute to the total current under forward conditions. 

Bock C, Pham DV, Kunze U, Kafer D, Witte G, Woll C (2006) Improved morphology and charge carrier injection in pentacene field-effect transistors with thiol-treated electrodes. J Appl Phys 100 114517... 

The electronic charge carriers injected into organic solids from ohmic contacts can build up a stable space charge by trapping in deep traps thus some dyes assume the properties of electrets on application of an electric field in the dark. According to Euler et al. 140>, this effect can be utilized for the storage of electrical energy. 

The electroluminescence was located in the part of the anthracene crystal next to the hole-injecting anode, which suggests an imbalance of charge-carrier injection and transport. The intensity of light was linearly proportional to the... 

Here, we define external EL quantum efficiency j (ext) by the ratio of the number of emitter photons outside the device divided by the number of charge carriers injected into the device. The internal EL quantum efficiency is defined by the number of photons produced within a device divided by the number of... 

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