Excitons in disordered organic semiconductors have been shown to diffuse only over the distances of 1-20 nm, thus limiting the efficiency of OPV cells.  Here, we show that diffusion of triplet excitons in highly ordered organic semiconductors (such as rubrene single crystals) can occur over macroscopic distances (2-8 �m), comparable to the light absorption length [H. Najafov et al., Nature Mater.  9, 938-943 (2010)]. Dissociation of these excitons at the surface of the crystal is found to be the main mechanism of photoconductivity in pristine highly ordered crystals. In combination with time-resolved measurements, optical functionalization of the surfaces with exciton splitters and modeling these observations strongly suggest that long-lived triplet excitons are indeed responsible for carrying the energy over macroscopic distances to the surface and surface dissociation into free charge carriers, representing an interesting concept for novel photovoltaic devices based on triplet organic materials.

Singlet exciton fission, long-range triplet exciton diffusion and   surface nature of photoconductivity in highly ordered organic semiconductors

243rd National Meeting (2012)

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