title: Organic dipole layers for ultralow work function electrodes.
abstract: The alignment of the electrode Fermi level with the valence or conduction bands of organic semiconductors is a key parameter controlling the efficiency of organic light-emitting diodes, solar cells, and printed circuits. Here, we introduce a class of organic molecules that form highly robust dipole layers, capable of shifting the work function of noble metals (Au and Ag) down to 3.1 eV, that is, ∼1 eV lower than previously reported self-assembled monolayers. The physics behind the considerable interface dipole is elucidated by means of photoemission spectroscopy and density functional theory calculations, and a polymer diode exclusively based on the surface modification of a single electrode in a symmetric, two-terminal Au/poly(3-hexylthiophene)/Au junction is presented. The diode exhibits the remarkable rectification ratio of ∼2·10(3), showing high reproducibility, durability (>3 years), and excellent electrical stability. With this evidence, noble metal electrodes with work function values comparable to that of standard cathode materials used in optoelectronic applications are demonstrated.
authors.affiliation: Materials Science Laboratory, Sony Deutschland GmbH , Hedelfinger Strasse 61, 70327 Stuttgart, Germany.
authors.forename: William E
authors.initials: WE
authors.lastname: Ford
authors.forename: Deqing
authors.initials: D
authors.lastname: Gao
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Knorr
authors.forename: Rene
authors.initials: R
authors.lastname: Wirtz
authors.forename: Frank
authors.initials: F
authors.lastname: Scholz
authors.forename: Zoi
authors.initials: Z
authors.lastname: Karipidou
authors.forename: Kodo
authors.initials: K
authors.lastname: Ogasawara
authors.forename: Silvia
authors.initials: S
authors.lastname: Rosselli
authors.forename: Vadim
authors.initials: V
authors.lastname: Rodin
authors.forename: Gabriele
authors.initials: G
authors.lastname: Nelles
authors.forename: Florian
authors.initials: F
authors.lastname: von Wrochem
keywords: injection barrier; interface dipole; molecular dipole; organic electronics; self-assembled monolayer; work function