Transport and Annihilation of the Triplets in Organic Phosphorescent Systems: Kinetic Monte Carlo Simulation and Modeling

We use kinetic Monte Carlo (kMC) simulations to study transport and annihilation of the triplet excitons in organic phosphorescent host-guest systems. By assuming a short-range hopping mechanism for the triplet transport and a long-range dipolar interaction for the triplet-triplet annihilation (TTA), we examine the effect of the relevant experimental parameters on the decay kinetics of the triplets in an energy-disordered system. It is shown that for the range of parameters typical of the organic host-guest systems, transport of the triplets at room temperature is dispersive during their lifetime, with a dispersion exponent of 0.4 < gamma < 0.6. We also provide a quantitative comparison between the kMC simulations and the traditional rate coefficients used to describe the TTA. We then suggest and justify a modified rate coefficient that can explain the TTA for a wide range of the system parameters. As the method of analysis, we focus on (a transformed) probability density function of the triplet decay and show that valuable insights into the statistics of the annihilation and the so-called efficiency roll-off can be obtained using this approach. We also discuss how and when describing the annihilation process in terms of an effective time-independent rate can be used to quantify the TTA in the host-guest systems. The results presented in this work are also relevant for other organic devices in which TTA plays a key role in the performance of the system.

Automated summary

The study uses kinetic Monte Carlo simulations to investigate the transport and annihilation of triplet excitons in organic phosphorescent host-guest systems. The results show that triplet transport in this system is dispersive during their lifetime under typical parameters, and a modified rate coefficient is proposed to explain the annihilation process. Valuable insights into the statistics of annihilation and efficiency roll-off are obtained through a probability density function analysis of triplet decay.