title: Space charge limited current measurements on conjugated polymer films using conductive atomic force microscopy.
abstract: We describe local (~150 nm resolution), quantitative measurements of charge carrier mobility in conjugated polymer films that are commonly used in thin-film transistors and nanostructured solar cells. We measure space charge limited currents (SCLC) through these films using conductive atomic force microscopy (c-AFM) and in macroscopic diodes. The current densities we measure with c-AFM are substantially higher than those observed in planar devices at the same bias. This leads to an overestimation of carrier mobility by up to 3 orders of magnitude when using the standard Mott-Gurney law to fit the c-AFM data. We reconcile this apparent discrepancy between c-AFM and planar device measurements by accounting for the proper tip-sample geometry using finite element simulations of tip-sample currents. We show that a semiempirical scaling factor based on the ratio of the tip contact area diameter to the sample thickness can be used to correct c-AFM current-voltage curves and thus extract mobilities that are in good agreement with values measured in the conventional planar device geometry.
authors.affiliation: Department of Chemistry, University of Washington, Seattle, WA 98195-1700, USA.
authors.forename: Obadiah G
authors.initials: OG
authors.lastname: Reid
authors.forename: Keiko
authors.initials: K
authors.lastname: Munechika
authors.forename: David S
authors.initials: DS
authors.lastname: Ginger
mesh_terms: D003198:Computer Simulation; D017097:Electric Impedance; D004574:Electromagnetic Fields; D008422:Materials Testing / Q000379:methods*; D018625:Microscopy, Atomic Force / Q000379:methods*; D008956:Models, Chemical; D011108:Polymers / Q000737:chemistry*; D012666:Semiconductors
chemical_list: D011108:Polymers