Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells

Oklobia, Ochai; Kartopu, Giray; Irvine, Stuart

doi:10.3390/ma12223706

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Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells

Ochai Oklobia, Giray Kartopu, Stuart Irvine

Materials, Volume: 12, Issue: 22, Start page: 3706

Swansea University Authors: Ochai Oklobia, Giray Kartopu, Stuart Irvine

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DOI (Published version): 10.3390/ma12223706

Abstract

As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe films were essentially insulating, the doped layers showed significant rise in conductivity with increasing As concentration....

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Published in:	Materials
ISSN:	1996-1944
Published:	MDPI AG 2019
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URI:	https://cronfa.swan.ac.uk/Record/cronfa52998
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first_indexed	2019-12-09T19:14:25Z
last_indexed	2021-08-19T03:24:28Z
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spelling	2021-08-18T14:36:47.4753760 v2 52998 2019-12-09 Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells d447e8d0345473fa625813546bccc592 Ochai Oklobia Ochai Oklobia true false 5c4917e0a29801844ec31737672f930c Giray Kartopu Giray Kartopu true false 1ddb966eccef99aa96e87f1ea4917f1f 0000-0002-1652-4496 Stuart Irvine Stuart Irvine true false 2019-12-09 MTLS As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe films were essentially insulating, the doped layers showed significant rise in conductivity with increasing As concentration. High p-type carrier densities up 4.5 × 1018 cm−3 was measured by the Hall-effect in heavily doped ZnTe:As films, displaying electrical properties comparable to epitaxial ZnTe single crystalline thin films in the literature. Device incorporation with as-deposited ZnTe:As yielded lower photovoltaic (PV) performance compared to reference devices, due to losses in the open-circuit potential (VOC) and fill factor (FF) related to reducing p-type doping density (NA) in the absorber layer. Some minor recovery observed in absorber doping following a Cl-free post–ZnTe:As deposition anneal in hydrogen at 420 °C contributed to a slight improvement in VOC and NA, highlighting the significance of back contact activation. A mild CdCl2 activation process on the ZnTe:As back contact layer via a sacrificial CdS cap layer has been assessed to suppress Zn losses, which occur in the case of standard CdCl2 anneal treatments (CHT) via formation of volatile ZnCl2. The CdS sacrificial cap was effective in minimising the Zn loss. Compared to untreated and non-capped, mild CHT processed ZnTe:As back contacted devices, mild CHT with a CdS barrier showed the highest recovery in absorber doping and an ~10 mV gain in VOC, with the best cell efficiency approaching the baseline devices. Journal Article Materials 12 22 3706 MDPI AG 1996-1944 ZnTe:As back contact; CdTe; thin films; solar cells; metalorganic chemical vapor deposition (MOCVD) 10 11 2019 2019-11-10 10.3390/ma12223706 COLLEGE NANME Materials Science and Engineering COLLEGE CODE MTLS Swansea University 2021-08-18T14:36:47.4753760 2019-12-09T13:30:25.6143077 Faculty of Science and Engineering School of Engineering and Applied Sciences - Materials Science and Engineering Ochai Oklobia 1 Giray Kartopu 2 Stuart Irvine 0000-0002-1652-4496 3 52998__16057__168534f6e3c44e33943b599ec0d30585.pdf oklobia2019.pdf 2019-12-09T13:32:23.2621319 Output 3165415 application/pdf Version of Record true Distributed under the terms of a Creative Commons Attribution (CC-BY-4.0) true eng http://creativecommons.org/licenses/by/4.0/
title	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
spellingShingle	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells Ochai Oklobia Giray Kartopu Stuart Irvine
title_short	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
title_full	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
title_fullStr	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
title_full_unstemmed	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
title_sort	Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells
author_id_str_mv	d447e8d0345473fa625813546bccc592 5c4917e0a29801844ec31737672f930c 1ddb966eccef99aa96e87f1ea4917f1f
author_id_fullname_str_mv	d447e8d0345473fa625813546bccc592_*_Ochai Oklobia 5c4917e0a29801844ec31737672f930c__Giray Kartopu 1ddb966eccef99aa96e87f1ea4917f1f_**_Stuart Irvine
author	Ochai Oklobia Giray Kartopu Stuart Irvine
author2	Ochai Oklobia Giray Kartopu Stuart Irvine
format	Journal article
container_title	Materials
container_volume	12
container_issue	22
container_start_page	3706
publishDate	2019
institution	Swansea University
issn	1996-1944
doi_str_mv	10.3390/ma12223706
publisher	MDPI AG
college_str	Faculty of Science and Engineering
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hierarchy_top_id	facultyofscienceandengineering
hierarchy_top_title	Faculty of Science and Engineering
hierarchy_parent_id	facultyofscienceandengineering
hierarchy_parent_title	Faculty of Science and Engineering
department_str	School of Engineering and Applied Sciences - Materials Science and Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Materials Science and Engineering
document_store_str	1
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description	As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe films were essentially insulating, the doped layers showed significant rise in conductivity with increasing As concentration. High p-type carrier densities up 4.5 × 1018 cm−3 was measured by the Hall-effect in heavily doped ZnTe:As films, displaying electrical properties comparable to epitaxial ZnTe single crystalline thin films in the literature. Device incorporation with as-deposited ZnTe:As yielded lower photovoltaic (PV) performance compared to reference devices, due to losses in the open-circuit potential (VOC) and fill factor (FF) related to reducing p-type doping density (NA) in the absorber layer. Some minor recovery observed in absorber doping following a Cl-free post–ZnTe:As deposition anneal in hydrogen at 420 °C contributed to a slight improvement in VOC and NA, highlighting the significance of back contact activation. A mild CdCl2 activation process on the ZnTe:As back contact layer via a sacrificial CdS cap layer has been assessed to suppress Zn losses, which occur in the case of standard CdCl2 anneal treatments (CHT) via formation of volatile ZnCl2. The CdS sacrificial cap was effective in minimising the Zn loss. Compared to untreated and non-capped, mild CHT processed ZnTe:As back contacted devices, mild CHT with a CdS barrier showed the highest recovery in absorber doping and an ~10 mV gain in VOC, with the best cell efficiency approaching the baseline devices.
published_date	2019-11-10T04:05:43Z
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score	11.037056

Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells

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