Clarifying the mechanism of triplet–triplet annihilation in phosphorescent organic host–guest systems: A combined experimental and simulation study

Abstract

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Förster-type triplet-polaron quenching in disordered organic semiconductors

“…That may be viewed as a result of a "competition" between polarons that can each quench the nearby triplet. An analogous effect has been theoretically predicted [16] and experimentally found [13,17] for the case of TTA at high initial triplet volume densities and from a KMC simulation study of NN-type TPQ [8].…”

“…The method is analogous to an approach that we have developed theoretically and applied successfully when analyzing the results of time-resolved PL experiments of triplet-triplet annihilation in host-guest systems used in OLEDs [13,16,17]. In the absence of diffusion, the formation of a depleted region gives rise to a distinct time dependence of the TPQ rate, as given within the continuum theory by Eqs.…”

“…IV, we have shown how the results of transient PL experiments can be used to investigate whether the TPQ process is in the intermediatediffusion regime. We have successfully used an analogous approach to analyze the contribution of exciton diffusion to the triplet-triplet annihilation rate coefficient [13,16,17] and expect that the method will be similarly useful to study tripletpolaron quenching.…”

Effect of polaron diffusion on exciton-polaron quenching in disordered organic semiconductors

“…The enhancement may be viewed as the result of a crossover to a regime in which the quench rate is increased due to a "competition" between various nearby polarons. From kMC simulations [26] and from experiment [27] we have found an analogous high-density enhancement of the rate coefficient for steady-state excitonexciton annihilation occurring at high exciton densities. We find that this continuum approach is not in all cases a good first starting point, as it does not include the finite probability p NN that after exciton generation immediate quenching takes place due to the presence of a polaron on a nearestneighbor lattice site.…”

“…We study the quenching of excitons in disordered organic semiconductor materials using the kinetic Monte Carlo (kMC) tool BUMBLEBEE [24] which has been explained extensively in earlier work on the rolloff [21,22,25], degradation [25], and triplet-triplet annihilation [26,27] in phosphorescent OLEDs. The systems considered are 100 × 100 × 100 nm 3 boxes in which the molecular sites reside on a simple cubic lattice with a lattice constant a.…”