Exciton migration in organic thin films

Limitations of the analytical method for calculating the exciton distribution in organic thin films, attributed to the improper boundary conditions when the organic film approaches the exciton diffusion length, were analyzed by comparison with an exciton random walk simulation. The random walk simulation results are in better agreement with in situ photoluminescence measurements than predictions based on the one-dimensional (1D) diffusion equation, especially for thin films (< 15 nm). The three-dimensional exciton diffusion length in tris(8-hydroxyquinoline) aluminum is determined to be 26 nm, equivalent to 15 nm upon projection to 1D. The result is not sensitive to the molecular size, a parameter arbitrarily set in the simulation. In addition, the exciton distribution in operating organic light emitting devices was also simulated. (c) 2006 American Institute of Physics.