High-Resolution Kelvin Probe Force Microscopy Imaging of Interface Dipoles and Photogenerated Charges in Organic Donor–Acceptor Photovoltaic Blends

• Published in: ACS nano Vol. 10; no. 1; pp. 739 - 746
• Main Authors: Fuchs, Franz, Caffy, Florent, Demadrille, Renaud, Mélin, Thierry, Grévin, Benjamin
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26.01.2016
• Subjects: Chemical Sciences; Engineering Sciences; Material chemistry; or physical chemistry; Physics; Theoretical and; surface photovoltage; organic photovoltaics; donor−acceptor interfaces; NC-AFM; KPFM
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.5b05810

We present noncontact atomic force microscopy and Kelvin probe force microscopy studies of nanophase segregated photovoltaic blends based on an oligothiophene–fluorenone oligomer and [6,6]-phenyl C70 butyric acid methyl ester. We carried out a complete analysis of the influence of the tip–surface interaction regime on the topographic, in-dark contact potential and surface photovoltage contrasts. It is demonstrated that an optimal lateral resolution is achieved for all channels below the onset of a contrast in the damping images. With the support of electrostatic simulations, it is shown that in-dark contact potential difference contrasts above subsurface acceptor clusters are consistent with an uneven distribution of permanent charges at the donor–acceptor interfaces. A remarkable dependence of the surface photovoltage magnitude with respect to the tip–surface distance is evidenced and attributed to a local enhancement of the electromagnetic field at the tip apex.