Influence of partially-oxidized silver back electrodes on the electrical properties and stability of organic semiconductor diodes

Zhongkai Cheng, Yan Wang, Deirdre M O'Carroll

Research output: Contribution to journalArticle

Abstract

Silver (Ag) is one of the most suitable metals for electrodes in high-performance organic optoelectronic devices due to its high conductivity and reflectivity, and low parasitic absorption loss at visible wavelengths. However, the electronic work function of Ag is not ideal for use as either the cathode or anode in many organic optoelectronic devices. In this report, we investigate the formation of an ultrathin surface oxide layer on a Ag electrode and its impact on hole injection into an organic conjugated polymer semiconductor. The surface oxide is formed by exposing the Ag electrode to a low-power O 2 /Ar plasma and which changes the electrical properties of the pure Ag electrode. We study the morphology and the chemical composition of the Ag surfaces after different plasma treatment times through X-ray photoelectron spectroscopy, scanning electron microscopy and dark-field optical microscopy. After plasma exposure the surface oxide is composed of both AgO x and Ag 2 CO 3 . As plasma exposure time increases from 1 s to 7 s, the fraction of AgO x increases while Ag 2 CO 3 decreases gradually. Both the turn-on voltages and barrier heights of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-only devices decrease with plasma treated Ag surfaces indicating that the work function of the Ag surface is increased by the surface oxide. F8BT hole-only devices with a thin MoO 3 layer and a thicker AgO x layer on the electrode are found to be stable compared to thinner surface oxides and un-treated Ag surfaces.

Original languageEnglish
Pages (from-to)179-185
Number of pages7
JournalOrganic Electronics: physics, materials, applications
Volume70
DOIs
Publication statusPublished - Jul 1 2019

Fingerprint

Semiconductor diodes
semiconductor diodes
Semiconducting organic compounds
organic semiconductors
Silver
Electric properties
electrical properties
silver
Electrodes
electrodes
Oxides
Plasmas
oxides
Carbon Monoxide
optoelectronic devices
Optoelectronic devices
Organic polymers
Conjugated polymers
Optical microscopy
Anodes

Keywords

  • Barrier height
  • Hole-only devices
  • Organic semiconductors
  • Plasma exposure
  • Silver oxide
  • Stability

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Chemistry(all)
  • Condensed Matter Physics
  • Materials Chemistry
  • Electrical and Electronic Engineering

Cite this

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title = "Influence of partially-oxidized silver back electrodes on the electrical properties and stability of organic semiconductor diodes",
abstract = "Silver (Ag) is one of the most suitable metals for electrodes in high-performance organic optoelectronic devices due to its high conductivity and reflectivity, and low parasitic absorption loss at visible wavelengths. However, the electronic work function of Ag is not ideal for use as either the cathode or anode in many organic optoelectronic devices. In this report, we investigate the formation of an ultrathin surface oxide layer on a Ag electrode and its impact on hole injection into an organic conjugated polymer semiconductor. The surface oxide is formed by exposing the Ag electrode to a low-power O 2 /Ar plasma and which changes the electrical properties of the pure Ag electrode. We study the morphology and the chemical composition of the Ag surfaces after different plasma treatment times through X-ray photoelectron spectroscopy, scanning electron microscopy and dark-field optical microscopy. After plasma exposure the surface oxide is composed of both AgO x and Ag 2 CO 3 . As plasma exposure time increases from 1 s to 7 s, the fraction of AgO x increases while Ag 2 CO 3 decreases gradually. Both the turn-on voltages and barrier heights of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-only devices decrease with plasma treated Ag surfaces indicating that the work function of the Ag surface is increased by the surface oxide. F8BT hole-only devices with a thin MoO 3 layer and a thicker AgO x layer on the electrode are found to be stable compared to thinner surface oxides and un-treated Ag surfaces.",
keywords = "Barrier height, Hole-only devices, Organic semiconductors, Plasma exposure, Silver oxide, Stability",
author = "Zhongkai Cheng and Yan Wang and O'Carroll, {Deirdre M}",
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T1 - Influence of partially-oxidized silver back electrodes on the electrical properties and stability of organic semiconductor diodes

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AU - Wang, Yan

AU - O'Carroll, Deirdre M

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N2 - Silver (Ag) is one of the most suitable metals for electrodes in high-performance organic optoelectronic devices due to its high conductivity and reflectivity, and low parasitic absorption loss at visible wavelengths. However, the electronic work function of Ag is not ideal for use as either the cathode or anode in many organic optoelectronic devices. In this report, we investigate the formation of an ultrathin surface oxide layer on a Ag electrode and its impact on hole injection into an organic conjugated polymer semiconductor. The surface oxide is formed by exposing the Ag electrode to a low-power O 2 /Ar plasma and which changes the electrical properties of the pure Ag electrode. We study the morphology and the chemical composition of the Ag surfaces after different plasma treatment times through X-ray photoelectron spectroscopy, scanning electron microscopy and dark-field optical microscopy. After plasma exposure the surface oxide is composed of both AgO x and Ag 2 CO 3 . As plasma exposure time increases from 1 s to 7 s, the fraction of AgO x increases while Ag 2 CO 3 decreases gradually. Both the turn-on voltages and barrier heights of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-only devices decrease with plasma treated Ag surfaces indicating that the work function of the Ag surface is increased by the surface oxide. F8BT hole-only devices with a thin MoO 3 layer and a thicker AgO x layer on the electrode are found to be stable compared to thinner surface oxides and un-treated Ag surfaces.

AB - Silver (Ag) is one of the most suitable metals for electrodes in high-performance organic optoelectronic devices due to its high conductivity and reflectivity, and low parasitic absorption loss at visible wavelengths. However, the electronic work function of Ag is not ideal for use as either the cathode or anode in many organic optoelectronic devices. In this report, we investigate the formation of an ultrathin surface oxide layer on a Ag electrode and its impact on hole injection into an organic conjugated polymer semiconductor. The surface oxide is formed by exposing the Ag electrode to a low-power O 2 /Ar plasma and which changes the electrical properties of the pure Ag electrode. We study the morphology and the chemical composition of the Ag surfaces after different plasma treatment times through X-ray photoelectron spectroscopy, scanning electron microscopy and dark-field optical microscopy. After plasma exposure the surface oxide is composed of both AgO x and Ag 2 CO 3 . As plasma exposure time increases from 1 s to 7 s, the fraction of AgO x increases while Ag 2 CO 3 decreases gradually. Both the turn-on voltages and barrier heights of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) hole-only devices decrease with plasma treated Ag surfaces indicating that the work function of the Ag surface is increased by the surface oxide. F8BT hole-only devices with a thin MoO 3 layer and a thicker AgO x layer on the electrode are found to be stable compared to thinner surface oxides and un-treated Ag surfaces.

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KW - Stability

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