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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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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 College of Engineering 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 College of Engineering
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hierarchy_top_title College of Engineering
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hierarchy_parent_title College of Engineering
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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 2019-11-10T04:16:31Z
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