Role of Exciton Density in Organic Materials: Diffusion Length, Lifetime, and Quantum Efficiency

Exciton dynamics are of pivotal importance in the working of organic electronic devices. Under conditions under which efficient exciton diffusion is combined with high excitation densities, exciton-exciton interactions become relevant, affecting significantly the diffusion length and average lifetimes of these excitations. Employing a kinetic Monte Carlo model, we investigate singlet exciton diffusion under conditions that span a wide range of organic materials. The contributions from the different deexcitation pathways are identified by analyzing simulated time-resolved photoluminescence spectra, allowing us to calculate the exciton densities at which exciton-exciton annihilation effects become dominant. The connection with actual materials of interest in applications is made, and the effects on exciton diffusion length and average lifetime are discussed.