The effects of optical interference on exciton diffusion length measurements using photocurrent spectroscopy

Wavelength-dependent measurements of photocurrent in single-layer devices are commonly used to determine the exciton diffusion length of organic thin films by comparing the Feng-Ghosh model for photocurrent response to experimental data. However, this model assumes that optical interference effects are negligible. For film thicknesses relevant to practical organic solar structures, optical interference effects cannot be avoided, leading to inaccurate estimates of the exciton diffusion length or apparent observation of two different types of excitons. This is illustrated for diindenoperylene and merocyanine thin films. The conditions under which a modified Feng-Ghosh model can be used are outlined. (C) 2008 American Institute of Physics.