title: Small molecule chemisorption on indium-tin oxide surfaces: enhancing probe molecule electron-transfer rates and the performance of organic light-emitting diodes.
abstract: Indium-tin oxide (ITO) surfaces have been modified by chemisorption of carboxylic acid functionalized small molecules: ferrocene dicarboxylic acid (1), 3-thiophene acetic acid (2), and 6-{4-[{4'-[[4-(5-carboxy-pentyloxy)-phenyl]-(4-methoxy-phenyl)-amino]-biphenyl-4-yl}-(4-methoxy-phenyl)-amino]-phenoxy}-hexanoic acid (p-OMe)2-TPD-(C5-COOH)2) (3). Voltammetrically determined surface coverages of 1-3 increased in two stages, the first stage completing in minutes, the latter stage taking several hours. Electron-transfer rate coefficients, kS, for the probe molecule ferrocene in acetonitrile likewise increased in two stages with increasing surface coverages of 1, 2, and 3. Fourier transform infrared spectroscopy of In2O3 powders, exposed for long periods to ethanol solutions of each modifier, confirmed the formation of indium oxalate-like surface species. X-ray photoelectron spectroscopy of carboxy-terminated alkanethiol-modified gold surfaces, exposed to these same In2O3(powder)/small molecule modifier solutions, showed the capture of trace levels of indium as a result of the chemisorption of these small molecules, suggesting that slow etching of the ITO surface also occurs during the chemisorption event. Conventional aluminum quinolate/bis-triarylamine organic light-emitting diodes (OLEDs) created on ITO surfaces modified with 1, 2, and 3, with and without an overlayer of PEDOT:PSS (a poly(thiophene)/poly(stryenesulfonate) ITO modifier), showed leakage currents lowered by several orders of magnitude and an increase in OLED device efficiency.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Chet
authors.initials: C
authors.lastname: Carter
authors.forename: Michael
authors.initials: M
authors.lastname: Brumbach
authors.forename: Carrie
authors.initials: C
authors.lastname: Donley
authors.forename: Richard D
authors.initials: RD
authors.lastname: Hreha
authors.forename: Seth R
authors.initials: SR
authors.lastname: Marder
authors.forename: Benoit
authors.initials: B
authors.lastname: Domercq
authors.forename: SeungHyup
authors.initials: S
authors.lastname: Yoo
authors.forename: Bernard
authors.initials: B
authors.lastname: Kippelen
authors.forename: Neal R
authors.initials: NR
authors.lastname: Armstrong
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000327:Adsorption; D001565:Benzoates / Q000737:chemistry*; D002208:Caproates / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D004159:Diphenylamine / Q000031:analogs & derivatives* / Q000737:chemistry; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D008027:Light; D000075163:Metallocenes; D015394:Molecular Structure; D010316:Particle Size; D012666:Semiconductors; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D013876:Thiophenes / Q000737:chemistry*; D017971:Tin Compounds / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: C517218:3-thiophene acetic acid; C517219:6-(4-((4'-((4-(5-carboxypentyloxy)phenyl)-(4-methoxyphenyl)amino)biphenyl-4-yl)-(4-methoxyphenyl)amino)phenoxy)hexanoic acid; D000085:Acetates; D001565:Benzoates; D002208:Caproates; D002264:Carboxylic Acids; D005296:Ferrous Compounds; D000075163:Metallocenes; D012996:Solutions; D013876:Thiophenes; D017971:Tin Compounds; C517217:ferrocene dicarboxylic acid; D014867:Water; C109984:indium tin oxide; D004159:Diphenylamine