Kelvin Probe Force Microscopy Study of Conjugated Polymer/Fullerene Organic Solar Cells

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Abstract
We conducted a comprehensive Kelvin probe force microscopy (KPFM) study of the "classical" organic solar cell system consisting of the MDMO-PPV:PCBM blend. The KPFM method yields detailed information of topography and local work function on the nanometer scale. Experiments were performed either in the dark or under laser illumination to extract locally resolved surface photovoltage. We identified distinct differences in energetics on the surface of chlorobenzene- and toluene-cast blend films. The electronic and structural behavior of the toluene-cast blend films were analyzed in relation to illumination and substrate temperature. Together with previous studies we were able to interpret the KPFM results and draw some conclusions regarding the correlation between the nanostructural properties and photovoltaic performance of organic solar cells.