Recombination at heterojunctions in disordered organic media: Modeling and numerical simulations

Abstract

Multilayer organic electroluminescent devices derive their advantages over their single-layer counterparts from the processes occurring at heterojunctions in organic media. These processes significantly differ from those in the bulk of the material. This paper presents three-dimensional modeling, numerical simulations, and a discussion of transport and recombination in a system with a heterojunction. We consider partial cross sections for the creation of excitons and exciplexes, and probabilities for recombination in the respective channels. We examine the influence of the energy barrier, electric field, site-energy disorder, and structural disorder at an organic-organic interface on transport and recombination. In particular, we investigate optimal parameter domains for recombination in the exciton channel. The interface roughness, unlike the site-energy disorder, is found to strongly affect the partial cross sections.

Effects of Gaussian disorder on charge carrier transport and recombination in organic semiconductors

“…The emergence of a filamentary current density as a result of energetic disorder has been revealed from various 3D studies, e.g., for systems with a uniform field and a uniform (average) carrier density 16, 80, in studies of the injection from a metallic electrode 81, of the unipolar 82, and bipolar 83 transport across organic–organic heterojunctions, and in devices with two metallic electrodes with varying injection conditions 76, 84. The filamentarity is strongest at small fields, decreases with increasing field, and vanishes at very high fields when almost all forward hops are “downhill” so that disorder has no effect anymore on the hop rates 16, 80.…”

“…Jurić et al 83 investigated the effect of 3D‐disorder on the recombination rate near an organic–organic heterojunction at which there are equal hole and electron barriers. With increasing disorder energy, a decreased effective recombination cross‐section at the barrier (leading to exciton or exciplex charge‐pairs) was found, as may be expected from the presence of rare low‐energy states which lead to an increased transmission probability through the barrier.…”

Progress in p -shell Λ hypernuclear spectroscopy

“…The 7 Λ Li excitation spectrum has been measured with 7 Li(π + , K + ) 7 Λ Li reactions in the E336 experiment. The observed Λ binding energy, B Λ = 5.22 ±0.08 (stat) ±0.36 (syst) MeV, agrees well with the emulsion data, B Λ = 5.58±0.03 MeV [7] . Besides this, four peaks were identified as excited states with excitation energies 2.05, 3.88, 5.61 and 7.99 MeV.…”

Simulation of Charge Carriers in Organic Electronic Devices: Methods with their Fundamentals and Applications

“…In fact, the apparent rate coefficients k were found to depend on charge density (including n and p), disorder, morphology, electric fields, and the presence of heterojunctions. [118,119,121,122,167] Though there are analytic expressions [168][169][170][171][172] that emerge from the theory of encounter, essentially based on Onsagers work [173] and on recent findings of Burke et al, [174] their use is, strictly speaking, limited to participating materials that are isotropic and homogeneous. Possible alternatives are empirical rate expressions, provided that they are justified for material and morphology in question.…”