The diffusion of fullerenes such as C 60 and PCBM in organic semiconductors is a key factor in controlling the effi ciency of organic solar cells, though it is challenging to measure and to control. A simple optical method based on photoluminescence quenching is developed to assess the diffusion of a quencher molecule such as C 60 through a semiconducting polymer fi lm, in this case made with the polymer polyfl uorene. When the mobility of the polymer chains is reduced by chemical crosslinking, the diffusion coeffi cient of C 60 can be reduced by up to three orders of magnitude.
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