The influence of MoO{sub x} gap states on hole injection from aluminum doped zinc oxide with nanoscale MoO{sub x} surface layer anodes for organic light emitting diodes

Journal Article · Fri Aug 14 00:00:00 EDT 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4928171· OSTI ID:22499253

Jha, Jitendra Kumar; Santos-Ortiz, Reinaldo; Du, Jincheng

The effective workfunction of Al doped ZnO films (AZO) increased from 4.1 eV to 5.55 eV after surface modification with nanoscale molybdenum sub-oxides (MoO{sub x}). Hole only devices with anodes consisting of 3 nm of MoO{sub x} on AZO exhibited a lower turn-on voltage (1.5 vs 1.8 V), and larger charge injection (190 vs 118 mA/cm{sup 2}) at the reference voltage, compared to indium tin oxide (ITO). AZO devices with 10 nm of MoO{sub x} exhibited the highest workfunction but performed poorly compared to devices with 3 nm of MoO{sub x}, or standard ITO. Ultraviolet photoelectron, X-ray photoelectron, and optical spectroscopies indicate that the 3 nm MoO{sub x} films are more reduced and farther away from MoO{sub 3} stoichiometry than their 10 nm equivalents. The vacancies associated with non-stoichiometry result in donor-like gap states which we assign to partially occupied Mo 4d levels. We propose that Fowler-Nordheim tunneling from these levels is responsible for the reduction in threshold voltage measured in devices with 3 nm of MoO{sub x}. A schematic band diagram is proposed. The thicker MoO{sub x} layers are more stoichiometric and resistive, and the voltage drop across these layers dominates their electrical performance, leading to an increase in threshold voltage. The results indicate that AZO with MoO{sub x} layers of optimal thickness may be potential candidates for anode use in organic light emitting diodes.

• OSTI ID: 22499253
• Journal Information: Journal of Applied Physics, Vol. 118, Issue 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
ALUMINIUM
ANODES
DOPED MATERIALS
ELECTRIC POTENTIAL
ELECTRONIC STRUCTURE
EV RANGE
HOLES
INDIUM COMPOUNDS
LIGHT EMITTING DIODES
MOLYBDENUM OXIDES
NANOSTRUCTURES
SPECTROSCOPY
STOICHIOMETRY
THIN FILMS
TIN OXIDES
TUNNEL EFFECT
ULTRAVIOLET RADIATION
VACANCIES
VOLTAGE DROP
X RADIATION
ZINC OXIDES