Abstract
We explore a facile and nontoxic hydrothermal route for synthesis of a Cu2ZnSnS4 nanocrystalline material by using l-cysteine as the sulfur source and ethylenediaminetetraacetic acid (EDTA) as the complexing agent. The effects of the amount of EDTA, the mole ratio of the three metal ions, and the hydrothermal temperature and time on the phase composition of the obtained product have been systematically investigated. The addition of EDTA and an excessive dose of ZnCl2 in the hydrothermal reaction system favor the generation of kesterite Cu2ZnSnS4. Pure kesterite Cu2ZnSnS4 has been synthesized at 180°C for 12 h from the reaction system containing 2 mmol of EDTA at 2:2:1 of Cu/Zn/Sn. It is confirmed by Raman spectroscopy that those binary and ternary phases are absent in the kesterite Cu2ZnSnS4 product. The kesterite Cu2ZnSnS4 material synthesized by the hydrothermal process consists of flower-like particles with 250 to 400 nm in size. It is revealed that the flower-like particles are assembled from single-crystal Cu2ZnSnS4 nanoflakes with ca. 20 nm in size. The band gap of the Cu2ZnSnS4 nanocrystalline material is estimated to be 1.55 eV. The films fabricated from the hierarchical Cu2ZnSnS4 particles exhibit fast photocurrent responses under intermittent visible-light irradiation, implying that they show potentials for use in solar cells and photocatalysis.
Highlights
The quaternary Cu2ZnSnS4 (CZTS) compound, derived from CuInS2 by replacing In(III) with Zn(II) and Sn(IV), has the advantages of optimum direct band gap for use in single-junction solar cells, abundance of the constituent elements, and high absorption coefficient (>104 cm−1) [1,2,3,4,5]
Effects of hydrothermal reaction conditions Amount of ethylenediaminetetraacetic acid (EDTA) In order to investigate the amount of EDTA on the phase composition of the obtained product, several samples have been synthesized at 180°C for 16 h by adding different amounts of EDTA into the reaction system with Cu/Zn/ Sn at 2:2:1
After 1 mmol of EDTA has been added into the reaction system, the obtained sample exhibits four main diffraction peaks of kesterite CZTS, together with one weak impurity peak located at 31.6°, which probably originates from CuS or Sn2S3
Summary
The quaternary Cu2ZnSnS4 (CZTS) compound, derived from CuInS2 by replacing In(III) with Zn(II) and Sn(IV), has the advantages of optimum direct band gap (around 1.5 eV) for use in single-junction solar cells, abundance of the constituent elements, and high absorption coefficient (>104 cm−1) [1,2,3,4,5]. If water is used to replace these organic solvents, a hydrothermal route will be developed, which is more desirable for the environment-friendly and low-cost synthesis of CZTS nanocrystalline materials. Few investigations on synthesis of CZTS nanocrystalline materials by the hydrothermal method have been reported, except the hydrothermal reactions with Na2S [31] or thiourea [32] as the sulfur source. In the current work, by the aid of ethylenediaminetetraacetic acid (EDTA) as a complexing agent, a low-cost and nontoxic hydrothermal route for synthesis of CZTS has been developed by using water as the solvent and L-cysteine as the sulfur source. The prepared CZTS nanocrystalline material has been employed to fabricate films, and the photoelectrochemical property of the obtained films has been evaluated
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