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Neutron reflectivity and X-ray scattering have been used to characterise the structure of photovoltaic optimised PCDTBT:PCBM (1:4) blend films. A negative gradient of the PCBM forms spontaneously upon film casting – a fortuitous structure that is well matched for efficient charge extraction. Mild thermal annealing at 70 °C does not significantly modify the film structure, and any improvement in device efficiency is likely to be through the removal of trapped casting solvent.
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Staniec et al. (2011) studied this question.
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