The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation

Matthew T. McDowell, Michael F. Lichterman, Azhar I. Carim, Rui Liu, Shu Hu, Bruce S. Brunschwig, Nathan S Lewis

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

Light absorbers with moderate band gaps (1-2 eV) are required for high-efficiency solar fuels devices, but most semiconducting photoanodes undergo photocorrosion or passivation in aqueous solution. Amorphous TiO2 deposited by atomic-layer deposition (ALD) onto various n-type semiconductors (Si, GaAs, GaP, and CdTe) and coated with thin films or islands of Ni produces efficient, stable photoanodes for water oxidation, with the TiO2 films protecting the underlying semiconductor from photocorrosion in pH = 14 KOH(aq). The links between the electronic properties of the TiO2 in these electrodes and the structure and energetic defect states of the material are not yet well-elucidated. We show herein that TiO2 films with a variety of crystal structures and midgap defect state distributions, deposited using both ALD and sputtering, form rectifying junctions with n-Si and are highly conductive toward photogenerated carriers in n-Si/TiO2/Ni photoanodes. Moreover, the photovoltage of these electrodes can be modified by annealing the TiO2 in reducing or oxidizing environments. All of the polycrystalline TiO2 films with compact grain boundaries investigated herein protected the n-Si photoanodes against photocorrosion in pH = 14 KOH(aq). Hence, in these devices, conduction through the TiO2 layer is neither specific to a particular amorphous or crystalline structure nor determined wholly by a particular extrinsic dopant impurity. The coupled structural and energetic properties of TiO2, and potentially other protective oxides, can therefore be controlled to yield optimized photoelectrode performance.

Original languageEnglish
Pages (from-to)15189-15199
Number of pages11
JournalACS Applied Materials and Interfaces
Volume7
Issue number28
DOIs
Publication statusPublished - Jul 22 2015

Fingerprint

Atomic layer deposition
Stabilization
Oxidation
Water
Processing
Semiconductor materials
Defects
Electrodes
Passivation
Electronic properties
Oxides
Sputtering
Grain boundaries
Energy gap
Crystal structure
Doping (additives)
Annealing
Impurities
Crystalline materials
Thin films

Keywords

  • heterojunction interfaces
  • oxygen evolution reaction
  • photocorrosion
  • photoelectrochemistry
  • solar fuels
  • water splitting

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation. / McDowell, Matthew T.; Lichterman, Michael F.; Carim, Azhar I.; Liu, Rui; Hu, Shu; Brunschwig, Bruce S.; Lewis, Nathan S.

In: ACS Applied Materials and Interfaces, Vol. 7, No. 28, 22.07.2015, p. 15189-15199.

Research output: Contribution to journalArticle

McDowell, Matthew T. ; Lichterman, Michael F. ; Carim, Azhar I. ; Liu, Rui ; Hu, Shu ; Brunschwig, Bruce S. ; Lewis, Nathan S. / The Influence of Structure and Processing on the Behavior of TiO2 Protective Layers for Stabilization of n-Si/TiO2/Ni Photoanodes for Water Oxidation. In: ACS Applied Materials and Interfaces. 2015 ; Vol. 7, No. 28. pp. 15189-15199.
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AU - Brunschwig, Bruce S.

AU - Lewis, Nathan S

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AB - Light absorbers with moderate band gaps (1-2 eV) are required for high-efficiency solar fuels devices, but most semiconducting photoanodes undergo photocorrosion or passivation in aqueous solution. Amorphous TiO2 deposited by atomic-layer deposition (ALD) onto various n-type semiconductors (Si, GaAs, GaP, and CdTe) and coated with thin films or islands of Ni produces efficient, stable photoanodes for water oxidation, with the TiO2 films protecting the underlying semiconductor from photocorrosion in pH = 14 KOH(aq). The links between the electronic properties of the TiO2 in these electrodes and the structure and energetic defect states of the material are not yet well-elucidated. We show herein that TiO2 films with a variety of crystal structures and midgap defect state distributions, deposited using both ALD and sputtering, form rectifying junctions with n-Si and are highly conductive toward photogenerated carriers in n-Si/TiO2/Ni photoanodes. Moreover, the photovoltage of these electrodes can be modified by annealing the TiO2 in reducing or oxidizing environments. All of the polycrystalline TiO2 films with compact grain boundaries investigated herein protected the n-Si photoanodes against photocorrosion in pH = 14 KOH(aq). Hence, in these devices, conduction through the TiO2 layer is neither specific to a particular amorphous or crystalline structure nor determined wholly by a particular extrinsic dopant impurity. The coupled structural and energetic properties of TiO2, and potentially other protective oxides, can therefore be controlled to yield optimized photoelectrode performance.

KW - heterojunction interfaces

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