Near-field photoconductivity imaging of a conjugated polymer blend

We report combined scanning near-field optical microscopy (SNOM) and near-field photocurrent (NPC) imaging of a binary conjugated polymer blend. We find phase separation on a scale of about 5 pm, with a good correspondence between topographic, fluorescence, and photocurrent images. We excited at 488 nm, a wavelength at which only one of the two polymers absorbs light. Under this illumination regions that are high in the topography image show high luminescence and photocurrent. The photoluminescence (PL) efficiencies in the different regions of the sample were determined by calculating the absorbed energy using the Bethe-Bouwkamp model, and knowledge about the chemical composition of the different phases of the polymer blend. The calculation also allowed us to conclude that the photocurrent generation efficiency (current/absorbed photons) of the different polymer phases is comparable within the limit of confidence of this experiment (+/-10%).