Exciton dynamics at interfaces of organic semiconductors

We review recent progress of using time-resolved two-photon photoelectron spectroscopy (2PPE) to study the energetics and dynamics of excitons at surfaces and interfaces of two prototypical organic semiconductors: C(60) and pentacene. For C(60) thin films epitaxially grown on Au(1 1 1) and Cu(1 1 1) surfaces, we observe both charge transfer and exciton states. For excitons in C(60), the proximity of a metal Surface leads to rapid, exciton band-mediated quenching. At the surface of pentacene thin films we observe a series of charge-transfer excitons where the electron and the photohole are bound across the interface. The ability of 2PPE to measure and directly relate exciton levels to single-electron levels is illustrated. (C) 2009 Elsevier B.V. All rights reserved.