Importance of indium tin oxide surface acido basicity for charge injection into organic materials based light emitting diodes

Abstract

The influence of the indium tin oxide (ITO) electrode surface acido basicity on organic electroluminescent device characteristics is studied. As measured by photoelectron spectroscopy, acid and base treatments produce large work function shifts of the oxide compared to standard ITO treated by an oxygen plasma or water. The current onsets for triphenyldiamine (TPD) single layer diodes sandwiched between ITO and a silver electrode are in qualitative agreement with the work function of the hole injecting oxide electrode. However, saturated photovoltage measurements on single layer diodes built on acid and water treated ITO disagree with the work function obtained from photoelectron experiments. This is explained by protonation of the diamine layer close to the electrode surface producing a charged double layer. It suggests that even acidic surface hydroxyl groups of the oxide electrode are able to protonate the diamine layer, explaining the importance of plasma cleaning to remove surface hydroxyls. The same ITO treatments are investigated in tris(8-hydroxyquinoline) (Alq) aluminum single layer diodes as well as hybrid TPD/Alq light emitting devices. Implications of metal–oxide surface acido basicity on electrode treatment and molecular material design are discussed.

Formation of metallic indium-tin phase from indium-tin-oxide nanoparticles under reducing conditions and its influence on the electrical properties

“…For reducing atmospheres either forming gas 10,19,20,22,23,[26][27][28][29][30] or low oxygen partial pressures 1,14,17,26,[31][32][33][34][35][36] are used. Furthermore, plasma treatments [37][38][39] as well as wet-chemical treatments [40][41][42] are ways to influence ITO's surface properties. The compilation in Table I shows the change of conductivity depending on the deposition method and postdeposition treatment.…”

Direct Measurement of Surface Complex Loading and Surface Dipole and Their Effect on Simple Device Behavior

“…[1][2][3][4][5][6][7] The Helmholtz expression derived from simple electrostatics, ∆φ ) qn∆µ ⊥ / r 0 , provides the conceptual basis for many practical attempts to enable this change in work function; here, q is the elementary charge, n is the surface dipole density, ∆µ ⊥ is the dipole moment perpendicular to the surface, r is the relative dielectric constant, and 0 is the vacuum permittivity. 8 An elegant model that has been proposed 9 within this context is based on an introduced dipole layer on the surface of the ITO: 10,11 If the negative end of the surface dipole species points away from the ITO surface, the work function of ITO is increased, and the hole injection barrier is decreased.…”

Electrical Characterizations of Schottky Diodes οn ITO Modified by Aromatic SAMs

“…Finally high purity Al (99%) was thermally evaporated to form the top contact cathode layer with a thickness of 120 nm at a pressure of 4 × 10 −6 Torr and a deposition rate of 3 Å/s in the same evaporation system. 3. Results and discussions 3.1.…”

“…The organic semiconductors and their derivatives are used as active components in the Schottky diode in recent years [2]. The rectication performance of the diodes depends on their electronic characteristics and interface properties [3]. The dierence between work functions of anode electrode and the adjacent organic layer determines the Schottky barrier properties at the metal/organic interface.…”