title: Fluorinated copper phthalocyanine nanowires for enhancing interfacial electron transport in organic solar cells.
abstract: Zinc oxide is a promising candidate as an interfacial layer (IFL) in inverted organic photovoltaic (OPV) cells due to the n-type semiconducting properties as well as chemical and environmental stability. Such ZnO layers collect electrons at the transparent electrode, typically indium tin oxide (ITO). However, the significant resistivity of ZnO IFLs and an energetic mismatch between the ZnO and the ITO layers hinder optimum charge collection. Here we report that inserting nanoscopic copper hexadecafluorophthalocyanine (F(16)CuPc) layers, as thin films or nanowires, between the ITO anode and the ZnO IFL increases OPV performance by enhancing interfacial electron transport. In inverted P3HT:PC(61)BM cells, insertion of F(16)CuPc nanowires increases the short circuit current density (J(sc)) versus cells with only ZnO layers, yielding an enhanced power conversion efficiency (PCE) of ∼3.6% vs ∼3.0% for a control without the nanowire layer. Similar effects are observed for inverted PTB7:PC(71)BM cells where the PCE is increased from 8.1% to 8.6%. X-ray scattering, optical, and electrical measurements indicate that the performance enhancement is ascribable to both favorable alignment of the nanowire π-π stacking axes parallel to the photocurrent flow and to the increased interfacial layer-active layer contact area. These findings identify a promising strategy to enhance inverted OPV performance by inserting anisotropic nanostructures with π-π stacking aligned in the photocurrent flow direction.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors.forename: Seok Min
authors.initials: SM
authors.lastname: Yoon
authors.forename: Sylvia J
authors.initials: SJ
authors.lastname: Lou
authors.forename: Stephen
authors.initials: S
authors.lastname: Loser
authors.forename: Jeremy
authors.initials: J
authors.lastname: Smith
authors.forename: Lin X
authors.initials: LX
authors.lastname: Chen
authors.forename: Antonio
authors.initials: A
authors.lastname: Facchetti
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks
authors.forename: Tobin
authors.initials: T
authors.lastname: Marks
mesh_terms: D011211:Electric Power Supplies; D004566:Electrodes; D004579:Electron Transport; D054879:Halogenation; D007211:Indoles / Q000737:chemistry*; D053770:Nanowires / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D012993:Solar Energy; D017971:Tin Compounds / Q000737:chemistry; D015034:Zinc Oxide / Q000737:chemistry
chemical_list: D007211:Indoles; D009942:Organometallic Compounds; D017971:Tin Compounds; C015445:copper phthalocyanine; C109984:indium tin oxide; D015034:Zinc Oxide