  We used broadband local dielectric spectroscopy (BLDS), an electric force
microscopy technique, to make non-contact measurements of conductivity in the
dark and under illumination of PM6:Y6 and Y6 prepared on ITO and PEDOT:PSS/ITO.
Over a range of illumination intensities, BLDS spectra were acquired and fit to
an impedance model of the tip-sample interaction to obtain a sample resistance
and capacitance. By comparing two descriptions of cantilever friction, an
impedance model and a microscopic model, we connected the sample resistance
inferred from impedance modeling to a microscopic sample conductivity. A charge
recombination rate was estimated from plots of the conductivity versus light
intensity and found to be sub-Langevin. The dark conductivity was orders of
magnitude higher than expected from Fermi-level equilibration of the PM6:Y6
with the substrate, suggesting that dark carriers may be a source of
open-circuit voltage loss in PM6:Y6.
