Nanoscale Polarization‐Resolved Surface Photovoltage of a Pleochroic Squaraine Thin Film

Local polarized surface photovoltage (SPV) spectroscopy is used to characterize an organic squaraine-fullerene photovoltaic layer blend. The anisotropic optical response of the textured photoactive layer is dominated by the largely Davydov-split absorption within the deep red of the crystallized donor compound. Through knowledge of the crystallographic texture, the local molecular in-plane orientation is deduced. Kelvin probe force microscopy (KPFM) maps the differential SPV of the active layer on the nanoscale without complications by interfaces, which is spatially correlated with the pleochroic optical response of the thin film. The SPV shows a wavelength-dependent, bichromatic change upon rotating the polarization axis of the illuminating light. With that subtler, nanoscaled optoelectronic sensing or actuating platforms become possible.