title: Consequences of anode interfacial layer deletion. HCl-treated ITO in P3HT:PCBM-based bulk-heterojunction organic photovoltaic devices.
abstract: In studies to simplify the fabrication of bulk-heterojunction organic photovoltaic (OPV) devices, it was found that when glass/tin-doped indium oxide (ITO) substrates are treated with dilute aqueous HCl solutions, followed by UV ozone (UVO), and then used to fabricate devices of the structure glass/ITO/P3HT:PCBM/LiF/Al, device performance is greatly enhanced. Light-to-power conversion efficiency (Eff) increases from 2.4% for control devices in which the ITO surface is treated only with UVO to 3.8% with the HCl + UVO treatment--effectively matching the performance of an identical device having a PEDOT:PSS anode interfacial layer. The enhancement originates from increases in V(OC) from 463 to 554 mV and FF from 49% to 66%. The modified-ITO device also exhibits a 4x enhancement in thermal stability versus an identical device containing a PEDOT:PSS anode interfacial layer. To understand the origins of these effects, the ITO surface is analyzed as a function of treatment by ultraviolet photoelectron spectroscopy work function measurements, X-ray photoelectron spectroscopic composition analysis, and atomic force microscopic topography and conductivity imaging. Additionally, a diode-based device model is employed to further understand the effects of ITO surface treatment on device performance.
authors.affiliation: Department of Chemistry, the Materials Research Center, and the Argonne Northwestern Solar Energy Research Institute, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Irwin
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Leever
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Servaites
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hersam
authors.forename: Michael F
authors.initials: MF
authors.lastname: Durstock
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks