The influence of annihilation processes on the threshold current density of organic laser diodes

Abstract

We examine the impact of various annihilation processes on the laser threshold current density of a multilayer organic laser diode by numerical simulation. Our self-consistent numerical model treats the dynamics of electrons, holes, and singlet as well as triplet excitons in the framework of a drift-diffusion model. The resulting particle distributions enter into an optical model. In our approach, a three layer waveguide structure is taken into account and the resulting laser rate equations are solved. Various annihilation processes are included as reactions between the different particle species in the device employing typical annihilation rates and material properties of organic semiconductors. By systematically varying the device dimensions and the annihilation rate coefficients, the dominating quenching processes are identified. The threshold current density is found to depend sensitively on the thickness of the emission layer. The influence of annihilation processes on the threshold current density is quantified as a function of the emission layer thickness and various annihilation rate coefficients. Using typical annihilation rate coefficients singlet-polaron annihilation is found to be the dominating quenching process. Maximum annihilation rate coefficients are calculated allowing a threshold current density below 1kA∕cm2. Singlet-triplet annihilation is recognized as another main loss process for singlet excitons. In our model the singlet exciton density is increased by triplet-triplet annihilation whereas it is diminished by singlet-triplet annihilation. The ratio of the rate coefficients for singlet-triplet and triplet-triplet annihilations is identified to be critical for the total number of singlet excitons being quenched by triplet excitons.

Organic solid‐state integrated amplifiers and lasers

“…They are formed either by intersystem-crossing (ISC) from the singlet state or by recombination of polarons. Since radiative recombination is forbidden in triplet states due to the mismatch of the electron and hole spins, it follows that triplets have long lifetimes, which leads to a significant build-up of their population [149,150]. The accumulation of triplet excitons limits the prospects for laser operation [151] as it reduces the singlet density via singlet-triplet annihilation www.lpr-journal.org…”

Exciton interaction with a spatially defined charge accumulation layer in the organic semiconductor diindenoperylene

“…It is rationalized that these processes are preferentially mediated by trapped holes. 7,8,9 Despite their importance, studies on the exciton loss mechanisms in neat organic single layers together with an estimation of the pivotal cross-sections are rather the exception, due to difficulties in precisely controlling the underlying boundary-conditions and in achieving a response of suited size to quantify the occurring loss processes.…”

“…It is rationalized that these processes are preferentially mediated by trapped holes. 7,8,9 Despite their importance, studies on the exciton loss mechanisms in neat organic single layers together with an estimation of the pivotal cross-sections are rather the exception, due to difficulties in precisely controlling the underlying boundary-conditions and in achieving a response of suited size to quantify the occurring loss processes.In this paper we focus on microscopic exciton quenching mechanisms induced by charge carriers and their investigation by photoluminescence (PL) quenching measurements on organic thin film transistor (OTFT) devices. This novel approach offers two essential advantages compared to studies on real opto-electronic devices.…”

“…Amongst which are exciton-exciton annihilation, where by non-radiative recombination of one electron-hole pair the remaining pair gains sufficient energy to overcome the Coulomb-binding energy required for dissociation, or charge carrier exchange accompanied by the formation of an energetically lower-lying triplet state. 7,8,9 Despite their importance, studies on the exciton loss mechanisms in neat organic single layers together with an estimation of the pivotal cross-sections are rather the exception, due to difficulties in precisely controlling the underlying boundary-conditions and in achieving a response of suited size to quantify the occurring loss processes.…”

Transparent amorphous oxide semiconductors for organic electronics: Application to inverted OLEDs

“…inverted OLEDs | electron injection | electron transport | amorphous oxide semiconductor | low work function material E lectronic and photonic devices based on organic semiconductors have attracted much attention due to their intrinsic characteristics that are difficult to achieve in inorganic semiconductors, such as flexibility and the capability of precise molecular design of active organic layers (1)(2)(3). However, organic devices suffer from the material properties that organic semiconductors in general have: rather high lowest unoccupied molecular orbital (LUMO) levels and low electron mobilities, such as 10 −6 to 10 −3 cm 2 /(V·s).…”