Device model investigation of bilayer organic light emitting diodes

Abstract

Organic materials that have desirable luminescence properties, such as a favorable emission spectrum and high luminescence efficiency, are not necessarily suitable for single layer organic light-emitting diodes (LEDs) because the material may have unequal carrier mobilities or contact limited injection properties. As a result, single layer LEDs made from such organic materials are inefficient. In this article, we present device model calculations of single layer and bilayer organic LED characteristics that demonstrate the improvements in device performance that can occur in bilayer devices. We first consider an organic material where the mobilities of the electrons and holes are significantly different. The role of the bilayer structure in this case is to move the recombination away from the electrode that injects the low mobility carrier. We then consider an organic material with equal electron and hole mobilities but where it is not possible to make a good contact for one carrier type, say electrons. The role of a bilayer structure in this case is to prevent the holes from traversing the device without recombining. In both cases, single layer device limitations can be overcome by employing a two organic layer structure. The results are discussed using the calculated spatial variation of the carrier densities, electric field, and recombination rate density in the structures.

The effect of morphology upon mobility: Implications for bulk heterojunction solar cells with nonuniform blend morphology

“…In both cases reducing the mobility reduces the current as expected. Our results are very similar to those of Crone et al, 23 who examined the consequence of a Case I type structure for light-emitting diodes. In the context of PV devices, SCL diodes are important because they are often used to derive mobilities for carriers within blend morphologies.…”

Device optimization of tris-aluminum (Alq3) based bilayer organic light emitting diode structures

“…While there has been significant progress in this area over recent years, comprehensive optical studies on device simulation and design have been scarce. The simulations of the charge transport and charge distribution in organic light emitting devices have been reported [3][4]. There have been several works on calculating the emission pattern [5] and external coupling in OLEDs [6].…”

Adaptive Finite Volume Simulation of Electrical Characteristics of Organic Light Emitting Diodes

“…1, we assume the length of anode (L A ) is equal to 20 nm, the length of cathode (L X ) is equal to 400 nm, and the thicknesses of Alq 3 layer (L y1 ) and TPD layer (L y2 ) are equal to 40 nm, respectively. We solve the steady-state DD model [11][12][13][14], which consists of ) (…”

“…We consider here the densities of trapped electrons and holes for the j th trap level where N tj (P tj ) is the electron (hole) trap density, E tj is the trap energy relative to the conduction band edge, g is the trap degeneracy, and E fn (E fp ) is the electron (hole) quasi-Fermi level. Boundary conditions are assumed for the DD model above [11][12][13][14].…”