Developing high-efficiency Cu2ZnSnS4 (CZTS) solar cells by controlling element distribution

UNSW, Sydney 2023

Cu2ZnSnS4 (CZTS) is one of the promising absorber materials for green thin film solar cells owing to its earth-abundant element composition, high absorption coefficient, tenable electrical properties, and suitable band gap for single junction solar cell and top cell for Si-based tandem solar cells. However, the development of CZTS solar cells in the past few years is still hindered by band- or potential-fluctuation and heavy recombination in bulk and interfaces that cause efficiency loss. In this thesis, some novel strategies are proposed to modify the element distribution in CZTS devices, and thus tackling these tough problems in different ways while boosting the efficiency of CZTS solar cells. Firstly, post-deposition annealing treatment (PDT) with excess or enough amounts of Ag salts on CZTS surface has been studied based on the preliminary device simulation. Simulation result shows that Ag-substitution on the shallow surface of CZTS can significantly enhance the VOC and thus the device performance. PDT with excess AgCl or the least amount of Ag2S can alloy Ag into shallow surface of CZTS, though the introduced non-radiative recombination centers within interface and bulk region deteriorate the device performance. Secondly, a mild Ag surface alloying strategy via Ag2ZnSnS4 top layer and an Al2O3 intermediate layer on a pre-sulfurized CZTS layer is proposed. The interface acceptor defect density can be reduced by an Al2O3 layer though it could not confine the Ag distribution at the surface region of CZTS. A moderate pre-sulfurization temperature can reduce the recombination at interface and voids area, boosting the efficiency to 8.75% without anti-reflecting coating. Next, the detrimental horizontal grain boundaries have been significantly mitigated by liquid-phase-assisted grain growth strategies via controlled decomposition of Cu2Zn(Sn,Ge)S4 bottom layer during sulfurization. The grain growth mechanism is studied in detail. The improved carrier collection effici

doctoral thesis; http://purl.org/coar/resource_type/c_db06

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English

LJ1 oai:unsworks.library.unsw.edu.au:1959.4/101490
1458861345

UNIV OF NEW S WALES
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