Asymptotic analysis of double-carrier, space-charge-limited transport in organic light-emitting diodes

Abstract

We analyse electron and hole transport in organic light-emitting diodes (OLEDs) via the drift-diffusion equations. We focus on space-charge-limited transport, in which rapid variations in charge carrier density occur near the injecting electrodes, and in which the electric field is highly non-uniform. This motivates our application of singular asymptotic analysis to the drift-diffusion equations. In the absence of electronhole recombination, our analysis reveals three regions within the OLED: (i) 'space-charge layers' near each electrode whose widthλ s is much smaller than the device widthL, wherein carrier densities decay rapidly and the electric field is intense; (ii) a 'bulk' region whose width is on the scale ofL, where carrier densities are small; and (iii) intermediate regions bridging (i) and (ii). Our analysis shows that the currentĴ scales asĴ ∝εμV 2 /L 2λ s , whereV is the applied voltage,ε is the permittivity andμ is the electric mobility, in contrast to the familiar diffusionfree scalingĴ ∝εμV 2 /L 3 . Thus, diffusion is seen to lead to a large O(L/λ s ) increase in current. Finally, we derive an asymptotic recombination-voltage relation for a kinetically limited OLED, in which charge recombination occurs on a much longer time scale than diffusion and drift.

Effect of Optical and Morphological Control of Single-Structured LEC Device

“…It can be seen that an irregular increase regardless of the emission layer thickness can be determined from the current-voltage relationship in the device with a double carrier. When the emission layer formed a thin film, the ion involved in the charge transfer is activated and follows the relational formula below [26]:…”

“…It can be seen that an irregular increase regardless of the emission layer thickness can be determined from the current–voltage relationship in the device with a double carrier. When the emission layer formed a thin film, the ion involved in the charge transfer is activated and follows the relational formula below [ 26 ]: ε is the dielectric constant, μ is the mobility, and V is the applied voltage; k B is the Boltzmann constant, T is the temperature, e is the charge of excitons, d is the thickness of the emission layer, and J is the current density. The λ s is defined as Equation (6): …”

Revisiting the methodological approach to some application oriented unipolar corona investigations focusing interfacial properties of the ionised region

“…A certain touch of cross-disciplinary view takes steps to give unintentional support to the line of reasoning stemming from (10). In short, the structure of this expression approximately evokes an improved formulation of the original Mott-Gurney (Child's law) [19]. In the realm of solid-state electronics, I q and I p are therefore representatives, in the same order, of a purely quadratic space-charge-limited current and a purely linear diffusional current.…”