Imaging the Carrier Photogeneration in Nanoscale Phase Segregated Organic Heterojunctions by Kelvin Probe Force Microscopy

In this work, we spatially resolve by Kelvin probe force microscopy (KPFM) under ultrahigh vacuum (UHV) the surface photovoltage in high-efficiency nanoscale phase segregated photovoltaic blends of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester. The spatial resolution achieved represents a 10-fold improvement over previous KPFM reports on organic solar cells. By combining the damping contrast to the topographic data in noncontact atomic force microscopy under UHV, surface morphologies of the interpenetrated networks are clearly revealed. We show how the lateral resolution in KPFM can be significantly enhanced by optimizing the damping signal, allowing a direct visualization of the carrier generation at the donor acceptor interfaces and their transport through the percolation pathways in the nanometer range. Henceforth, high-resolution KPFM has the potential to become a routine characterization tool for organic and hybrid photovoltaics.