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

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

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


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 languageEnglish (US)
Article number565
Issue number3
StatePublished - 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.


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

MRSEC Support

  • Shared

PubMed: MeSH publication types

  • Journal Article


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