Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups

Chengjian Zhang; Qiaomiao Tu; Lorraine F Francis; Uwe R. Kortshagen

doi:10.3390/nano12030565

Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups

Chengjian Zhang, Qiaomiao Tu, Lorraine F Francis, Uwe R. Kortshagen

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22 Scopus citations

Abstract

Transparent conductive oxides (TCOs) are widely used in optoelectronic devices such as flat-panel displays and solar cells. A significant optical property of TCOs is their band gap, which determines the spectral range of the transparency of the material. In this study, a tunable band gap range from 3.35 eV to 3.53 eV is achieved for zinc oxide (ZnO) nanocrystals (NCs) films synthesized by nonthermal plasmas through the removal of surface groups using atomic layer deposition (ALD) coating of Al₂ O₃ and intense pulsed light (IPL) photo-doping. The Al₂ O₃ coating is found to be necessary for band gap tuning, as it protects ZnO NCs from interactions with the ambient and prevents the formation of electron traps. With respect to the solar spectrum, the 0.18 eV band gap shift would allow ~4.1% more photons to pass through the transparent layer, for instance, into a CH₃ NH₃ PbX₃ solar cell beneath. The mechanism of band gap tuning via photo-doping appears to be related to a combination of the Burstein–Moss (BM) and band gap renormalization (BGN) effects due to the significant number of electrons released from trap states after the removal of hydroxyl groups. The BM effect shifts the conduction band edge and enlarges the band gap, while the BGN effect narrows the band gap.

Original language	English (US)
Article number	565
Journal	Nanomaterials
Volume	12
Issue number	3
DOIs	https://doi.org/10.3390/nano12030565
State	Published - Feb 1 2022

Bibliographical note

Funding Information:
Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award Number DMR-2011401) and the NNCI (Award Number ECCS-2025124) programs. Parts of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nanotechnology Coordinated Infrastructure (NNCI) under Award Number ECCS-2025124.

Publisher Copyright:
© 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Keywords

Atomic layer deposition
Band gap
Band gap renormalization
Burstein–Moss effect
Intense pulsed light
Metal oxide nanocrystals
Nonthermal plasmas

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title = "Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups",

abstract = "Transparent conductive oxides (TCOs) are widely used in optoelectronic devices such as flat-panel displays and solar cells. A significant optical property of TCOs is their band gap, which determines the spectral range of the transparency of the material. In this study, a tunable band gap range from 3.35 eV to 3.53 eV is achieved for zinc oxide (ZnO) nanocrystals (NCs) films synthesized by nonthermal plasmas through the removal of surface groups using atomic layer deposition (ALD) coating of Al2 O3 and intense pulsed light (IPL) photo-doping. The Al2 O3 coating is found to be necessary for band gap tuning, as it protects ZnO NCs from interactions with the ambient and prevents the formation of electron traps. With respect to the solar spectrum, the 0.18 eV band gap shift would allow \textasciitilde{}4.1\% more photons to pass through the transparent layer, for instance, into a CH3 NH3 PbX3 solar cell beneath. The mechanism of band gap tuning via photo-doping appears to be related to a combination of the Burstein–Moss (BM) and band gap renormalization (BGN) effects due to the significant number of electrons released from trap states after the removal of hydroxyl groups. The BM effect shifts the conduction band edge and enlarges the band gap, while the BGN effect narrows the band gap.",

keywords = "Atomic layer deposition, Band gap, Band gap renormalization, Burstein–Moss effect, Intense pulsed light, Metal oxide nanocrystals, Nonthermal plasmas",

author = "Chengjian Zhang and Qiaomiao Tu and Francis, \{Lorraine F\} and Kortshagen, \{Uwe R.\}",

note = "Funding Information: Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award Number DMR-2011401) and the NNCI (Award Number ECCS-2025124) programs. Parts of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nanotechnology Coordinated Infrastructure (NNCI) under Award Number ECCS-2025124. Publisher Copyright: {\textcopyright} 2022 by the authors. Licensee MDPI, Basel, Switzerland.",

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doi = "10.3390/nano12030565",

language = "English (US)",

volume = "12",

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AU - Zhang, Chengjian

AU - Tu, Qiaomiao

AU - Francis, Lorraine F

AU - Kortshagen, Uwe R.

N1 - Funding Information: Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award Number DMR-2011401) and the NNCI (Award Number ECCS-2025124) programs. Parts of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nanotechnology Coordinated Infrastructure (NNCI) under Award Number ECCS-2025124. Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - Transparent conductive oxides (TCOs) are widely used in optoelectronic devices such as flat-panel displays and solar cells. A significant optical property of TCOs is their band gap, which determines the spectral range of the transparency of the material. In this study, a tunable band gap range from 3.35 eV to 3.53 eV is achieved for zinc oxide (ZnO) nanocrystals (NCs) films synthesized by nonthermal plasmas through the removal of surface groups using atomic layer deposition (ALD) coating of Al2 O3 and intense pulsed light (IPL) photo-doping. The Al2 O3 coating is found to be necessary for band gap tuning, as it protects ZnO NCs from interactions with the ambient and prevents the formation of electron traps. With respect to the solar spectrum, the 0.18 eV band gap shift would allow ~4.1% more photons to pass through the transparent layer, for instance, into a CH3 NH3 PbX3 solar cell beneath. The mechanism of band gap tuning via photo-doping appears to be related to a combination of the Burstein–Moss (BM) and band gap renormalization (BGN) effects due to the significant number of electrons released from trap states after the removal of hydroxyl groups. The BM effect shifts the conduction band edge and enlarges the band gap, while the BGN effect narrows the band gap.

AB - Transparent conductive oxides (TCOs) are widely used in optoelectronic devices such as flat-panel displays and solar cells. A significant optical property of TCOs is their band gap, which determines the spectral range of the transparency of the material. In this study, a tunable band gap range from 3.35 eV to 3.53 eV is achieved for zinc oxide (ZnO) nanocrystals (NCs) films synthesized by nonthermal plasmas through the removal of surface groups using atomic layer deposition (ALD) coating of Al2 O3 and intense pulsed light (IPL) photo-doping. The Al2 O3 coating is found to be necessary for band gap tuning, as it protects ZnO NCs from interactions with the ambient and prevents the formation of electron traps. With respect to the solar spectrum, the 0.18 eV band gap shift would allow ~4.1% more photons to pass through the transparent layer, for instance, into a CH3 NH3 PbX3 solar cell beneath. The mechanism of band gap tuning via photo-doping appears to be related to a combination of the Burstein–Moss (BM) and band gap renormalization (BGN) effects due to the significant number of electrons released from trap states after the removal of hydroxyl groups. The BM effect shifts the conduction band edge and enlarges the band gap, while the BGN effect narrows the band gap.

KW - Atomic layer deposition

KW - Band gap

KW - Band gap renormalization

KW - Burstein–Moss effect

KW - Intense pulsed light

KW - Metal oxide nanocrystals

KW - Nonthermal plasmas

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DO - 10.3390/nano12030565

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SN - 2079-4991

VL - 12

JO - Nanomaterials

JF - Nanomaterials

IS - 3

M1 - 565

ER -

Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups

Abstract

Bibliographical note

Keywords

MRSEC Support

PubMed: MeSH publication types

UN SDGs

Publisher link

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University of Minnesota Materials Research Science and Engineering Center (DMR-2011401)

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Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups

Abstract

Bibliographical note

Keywords

MRSEC Support

PubMed: MeSH publication types

UN SDGs

Publisher link

Find It

Other files and links

Fingerprint

Projects

University of Minnesota Materials Research Science and Engineering Center (DMR-2011401)

Cite this