Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups
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...
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| Format: | Article |
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MDPI AG
2022-02-01
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| Series: | Nanomaterials |
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| Online Access: | https://www.mdpi.com/2079-4991/12/3/565 |
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| author | Chengjian Zhang Qiaomiao Tu Lorraine F. Francis Uwe R. Kortshagen |
| author_facet | Chengjian Zhang Qiaomiao Tu Lorraine F. Francis Uwe R. Kortshagen |
| author_sort | Chengjian Zhang |
| collection | DOAJ |
| description | 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 Al<sub>2</sub>O<sub>3</sub> and intense pulsed light (IPL) photo-doping. The Al<sub>2</sub>O<sub>3</sub> 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 CH<sub>3</sub>NH<sub>3</sub>PbX<sub>3</sub> 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. |
| first_indexed | 2024-03-09T23:23:47Z |
| format | Article |
| id | doaj.art-cda92964c6f8498aa4c18ed1b1157bdd |
| institution | Directory Open Access Journal |
| issn | 2079-4991 |
| language | English |
| last_indexed | 2024-03-09T23:23:47Z |
| publishDate | 2022-02-01 |
| publisher | MDPI AG |
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| series | Nanomaterials |
| spelling | doaj.art-cda92964c6f8498aa4c18ed1b1157bdd2023-11-23T17:22:52ZengMDPI AGNanomaterials2079-49912022-02-0112356510.3390/nano12030565Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface GroupsChengjian Zhang0Qiaomiao Tu1Lorraine F. Francis2Uwe R. Kortshagen3Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414, USADepartment of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414, USADepartment of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414, USADepartment of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55414, USATransparent 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 Al<sub>2</sub>O<sub>3</sub> and intense pulsed light (IPL) photo-doping. The Al<sub>2</sub>O<sub>3</sub> 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 CH<sub>3</sub>NH<sub>3</sub>PbX<sub>3</sub> 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.https://www.mdpi.com/2079-4991/12/3/565metal oxide nanocrystalsband gapBurstein–Moss effectband gap renormalizationnonthermal plasmasatomic layer deposition |
| spellingShingle | Chengjian Zhang Qiaomiao Tu Lorraine F. Francis Uwe R. Kortshagen Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups Nanomaterials metal oxide nanocrystals band gap Burstein–Moss effect band gap renormalization nonthermal plasmas atomic layer deposition |
| title | Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups |
| title_full | Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups |
| title_fullStr | Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups |
| title_full_unstemmed | Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups |
| title_short | Band Gap Tuning of Films of Undoped ZnO Nanocrystals by Removal of Surface Groups |
| title_sort | band gap tuning of films of undoped zno nanocrystals by removal of surface groups |
| topic | metal oxide nanocrystals band gap Burstein–Moss effect band gap renormalization nonthermal plasmas atomic layer deposition |
| url | https://www.mdpi.com/2079-4991/12/3/565 |
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