title: Surface characterization of polythiophene:fullerene blends on different electrodes using near edge X-ray absorption fine structure.
abstract: We study the top surface composition of blends of the conjugated polymer regioregular poly-3-hexylthiophene (P3HT) with the fullerene (6,6)-phenyl-C(61)-butyric acid methyl ester (PCBM), an important model system for organic photovoltaics (OPVs), using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). We compare the ratio of P3HT to PCBM near the air/film interface that results from preparing blend films on two sets of substrates: (1) poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) coated indium tin oxide (ITO) as is commonly used in conventional OPV structures and (2) ZnO substrates that are either unmodified or modified with a C(60)-like self-assembled monolayer, similar to those that have been recently reported in inverted OPV structures. We find that the top surface (the film/air interface) is enriched in P3HT compared to the bulk, regardless of substrate or annealing conditions, indicating that changes in device performance due to substrate modification treatments should be attributed to the buried substrate/film interface and the bulk of the film rather than the exposed film/air interface.
authors.affiliation: Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States.
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Tillack
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Noone
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Macleod
authors.forename: Dennis
authors.initials: D
authors.lastname: Nordlund
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Nagle
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Bradley
authors.forename: Steven K
authors.initials: SK
authors.lastname: Hau
authors.forename: Hin-Lap
authors.initials: HL
authors.lastname: Yip
authors.forename: Alex K-Y
authors.initials: AK
authors.lastname: Jen
authors.forename: Gerald T
authors.initials: GT
authors.lastname: Seidler
authors.forename: David S
authors.initials: DS
authors.lastname: Ginger
mesh_terms: D004566:Electrodes; D004867:Equipment Design; D019544:Equipment Failure Analysis; D037741:Fullerenes / Q000737:chemistry*; D008422:Materials Testing; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013876:Thiophenes / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D037741:Fullerenes; D011108:Polymers; D013876:Thiophenes; C066730:polythiophene