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The role of entropy in charge separation processes is discussed with respect to the dimensionality of the organic semiconductor. In 1-D materials, the change in entropy, ΔS, plays no role, but at higher dimensions, it leads to a substantial decrease in the Coulomb barrier for charge separation. The effects of ΔS are highest in equilibrium systems but decrease and become time-dependent in illuminated organic photovoltaic (OPV) cells. Higher-dimensional semiconductors have inherent advantages for charge separation, and this may be one reason that C60 and its derivatives, the only truly three-dimensional organic semiconductors yet known, play such an important role in OPV cells.
Brian A. Gregg (Wed,) studied this question.