Electronic and chemical properties of molybdenum oxide doped hole injection layers in organic light emitting diodes

Abstract

The origins of barrier lowering leading to high efficient organic light emitting devices with incorporation of molybdenum oxide (MoOx) in anode structures are investigated. Ultraviolet and x-ray photoemission spectra reveal that p-type doping effects in the organic films and carrier concentration increase at the anode interfaces cause the hole injection barrier lowering. The gap states, which help carrier injection from the anodes, resulted from the oxygen deficiency in MoOx due to the interaction of organic materials and MoOx.

Electronic structure of MoO3−x/graphene interface

“…The hole injection barrier decreases from 2.78 to 0.53 eV owing to the presence of the defect state (gap state) in MoO 3Àx . This result is consistent with the previous report on the MoO 3Àx /ITO interfaces [21,22], and provides useful guidance in fabricating organic electronic devices using graphene as anode and MoO 3Àx as HIL. Charge density q (a. u) Thickness of MoO 3-x films (nm) …”

“…Among the oxides, MoO 3 is the most studied because of its easy processing and relatively high refractive index [18,19]. Several reports showed that the performance of organic electronic devices increased with the introduction of MoO 3 HIL [20,21]. The HIL is essential for better band alignment between the anode and organic hole transport layer in OLED or OPV devices.…”

Organic-inorganic heterojunction field-effect transistors

“…Moreover, the organic-inorganic heterojunction can improve the physical contact between the metal electrode and organic film, which was widely applied in OFET and organic diodes. [20][21][22][23][24][25][26] …”

“…16,17 Inorganic materials have also been introduced into various organic electronic devices. [18][19][20][21][22][23][24][25] For example, pentacene/ zinc oxide ͑ZnO͒ bilayer transistors with different operation modes have been obtained by varying the thickness of ZnO layer. 19 Transition metal oxides are often used as a buffer layer between organic semiconductor and metal for performance enhancement.…”

“…19 Transition metal oxides are often used as a buffer layer between organic semiconductor and metal for performance enhancement. [20][21][22][23][24][25] For OFETs, 26 inserting a transition metal oxide between the source-drain electrodes and organic active layer can greatly reduce contact resistance. Recently, the shift of threshold voltage was observed in single crystal OFET when molybdenum trioxide ͑MoO 3 ͒ was deposited on the surface of p-bis͓͑p-styryl͒styryl͔ benzene single crystal, and electron transfer was suggested to explain this phenomenon.…”