Ex-situ Ge-doping of CZTS Nanocrystals and CZTSSe Solar Absorber Films

Naylor, Matthew, Tiwari, Devendra, Sheppard, Alice, Laverock, Jude, Campbell, Stephen, Ford, Bethan, Xu, Xinya, Jones, Michael, Qu, Yongtao, Maiello, Pietro, Barrioz, Vincent, Beattie, Neil, Fox, Neil A., Fermin, David J. and Zoppi, Guillaume (2022) Ex-situ Ge-doping of CZTS Nanocrystals and CZTSSe Solar Absorber Films. Faraday Discussions. ISSN 1364-5498 (In Press)

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Abstract

Cu2ZnSn(S,Se)4 (CZTSSe) is a promising material for thin-film photovoltaics however the open-circuit voltage (VOC) deficit of CZTSSe prevents device performance to exceed 13 conversion efficiency. CZTSSe is a heavily compensated material that is rich in point defects and prone to the formation of secondary phases. The landscape of these defects is complex and some mitigation is possible by employing non-stoichiometric conditions. Another route used to reduce the effects of undesirable defects is doping and alloying of the material to suppress certain defects and improve crystallization such as germanium. The majority of works deposit Ge adjacent to a stacked metallic precursor deposited by physical vapour deposition before annealing in a selenium rich atmosphere. Here we use an established hot-injection process to synthesise Cu2ZnSnS4 nanocrystals of a pre-determined composition, subsequently doped with Ge during selenisation to aid recrystallisation and reduce the effects of Sn species. Through Ge incorporation we demonstrate structural changes with negligible change in energy bandgap but substantial increase in crystallinity and grain morphology which is associated to a Ge-Se growth mechanism and gains in both VOC and conversion efficiency. We use surface energy-filtered photoelectron emission microscopy (EF-PEEM) to map the surface work function terrains and show an improved electronic landscape which we attribute to a reduction in segregation of low local effective work function (LEWF) Sn(II) chalcogenide phases.

Item Type: Article
Additional Information: Funding information: This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) via grants EP/S023836/1, EP/V008692/1, EP/V008676/1, EP/L017792/1, and EP/T005491/1. We are thankful for EPSRC strategic equipment grants EP/K035746/1 and EP/M000605/1. The authors also appreciate the support from the North East Centre for Energy Materials (NECEM) (EP/R021503/1), the British Council Newton Fund Institutional Links Grant (CRP01286) and the Royal Society of Chemistry (E20-9404). The authors thank and acknowledge use of the University of Bristol NanoESCA II Laboratory.
Subjects: F100 Chemistry
F200 Materials Science
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 29 Apr 2022 10:57
Last Modified: 29 Apr 2022 11:09
URI: http://nrl.northumbria.ac.uk/id/eprint/49001

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