Temperature Dependence of Cu$_{2}$ZnSnS$_{4}$ Photovoltaic Cell Properties

Tajima, S.; Katagiri, Hironori; Jimbo, Kazuo; Sugimoto, Noriaki; Fukano, Tohru

doi:10.1143/apex.5.082302

Cited by 21 publications

(15 citation statements)

References 11 publications

(16 reference statements)

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“…All the extrapolated V OC values at 0 K were approximately 1.2 V, regardless of the process conditions and compositions of the CZTS layers, which were lower than the E g of CZTS. 16) This result indicates that recombination processes at the interface of the CdS=CZTS layers, were dominant in these samples. Our two-layer structure is effective for improving V OC ; however, improvements to the interface of the CdS=CZTS layers are also imperative in order to achieve a higher V OC .…”

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confidence: 84%

Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure

Tajima

Itoh

Hazama

et al. 2015

Appl. Phys. Express

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In Cu 2 ZnSnS 4 (CZTS) photovoltaic cells, a low open-circuit voltage (V OC ) principally causes low conversion efficiency. We investigated the deposition of a CZTS layer by a two-layer process to improve the V OC of the CZTS cells. In this process, the first CZTS layers near a Mo electrode have a high Cu content and the second layer near the surface has a low Cu content. The two-layer process improved the V OC of the CZTS cells from 0.66 to 0.78 V. Finally, the best CZTS cell showed a conversion efficiency of 8.8%. R ecently, the production of compound thin-film photovoltaic cells, for example, the Cu(In,Ga)Se 2 and CdTe types, has been increasing annually. However, the materials used to make these cells include rare metals (In and Ga), which significantly limits the volume that can be produced. The thin-film photovoltaic material Cu 2 ZnSnS x Se 4−x (CZTSSe) has recently become a candidate material for new photovoltaic cells. Wang et al. recently reported the production of CZTS 0.2 Se 0.8 thin-film solar cells with a conversion efficiency of 12.6%. 2) However, CZTSSe contains Se, a harmful element, and has a band-gap energy (E g ) of 1.1 eV, which is smaller than the optimum E g of 1.4-1.5 eV for the solar spectrum. On the other hand, Cu 2 ZnSnS 4 (CZTS) has been attracting increasing attention as a candidate material 1) because it contains no rare (In and Ga) or harmful (Se and Te) elements, and has a suitable E g of 1.4 eV. However, the CZTS cells that were previously reported have efficiencies below 10%. [3][4][5][6] Consequently, for the mass production of photovoltaic cells, it is clear that the development of CZTS cells with high efficiency is required.One of the main reasons for the poor photovoltaic properties of CZTS cells is their open-circuit voltage (V OC ), which is lower than that expected from the E g . The low V OC directly results in low conversion efficiency. To understand the V OC of the CZTS cells, the conduction band offset (CBO) at the interface between the buffer and the CZTS layers should be examined. In general, the interface between the buffer layer and the absorber layer is categorized into either a "cliff " or a "spike" type, where a large cliff lowers V OC and a large spike reduces the short-circuit current density (J SC ). 7,8) Researchers previously reported on the evaluation of the CBO value at the interface between the CdS and CZTS layers using methods such as hard X-ray photoelectron spectroscopy, 9) pump=probe methods [ultraviolet photoelectron spectroscopy (UPS)], 10) and UPS=inverse photoelectron spectroscopy (IPES), 11) and showed it to be sufficiently small, in the range from +0.4 to −0.2 eV, to realize a high-performance cell. Therefore, the CBO value is not the main reason for the low V OC in the CZTS cells.Another possible reason for the low V OC is the influence of an inner potential between the CZTS and window layers. In other words, the lower inner potential between the CZTS and window layers can cause a lower V OC when the hole carrier concentration (N c ) of the CZ...

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confidence: 84%

Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure

Tajima

Itoh

Hazama

et al. 2015

Appl. Phys. Express

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“…A trace amount of Cd(S,O,OH) and the resultant interfacial defects could contribute to recombination. 18 After the 573 K annealing step, the concentration of oxygen decreased and Cd(S,O,OH) transformed to CdS. Consequently, the crystallinity of the CdS layers was also improved with the annealing as shown in Fig.…”

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Atom-probe tomographic study of interfaces of Cu2ZnSnS4 photovoltaic cells

Tajima¹,

Asahi²,

Isheim³

et al. 2014

Applied Physics Letters

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The heterophase interfaces between the CdS buffer layer and the Cu2ZnSnS4 (CZTS) absorption layers are one of the main factors affecting photovoltaic performance of CZTS cells. We have studied the compositional distributions at heterophase interfaces in CZTS cells using three-dimensional atom-probe tomography. The results demonstrate: (a) diffusion of Cd into the CZTS layer; (b) segregation of Zn at the CdS/CZTS interface; and (c) a change of oxygen and hydrogen concentrations in the CdS layer depending on the heat treatment. Annealing at 573 K after deposition of CdS improves the photovoltaic properties of CZTS cells probably because of the formation of a heterophase epitaxial junction at the CdS/CZTS interface. Conversely, segregation of Zn at the CdS/CZTS interface after annealing at a higher temperature deteriorates the photovoltaic properties.

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“…evaporation and sputtering, or by non-vacuum method such as spray pyrolysis, printing, etc. [9][10][11][12]. The CZTS solar cells fabricated by vacuum method have shown/ show a lower efficiency than that of non-vacuum methods [13][14][15][16].…”

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confidence: 99%

Effects of annealing conditions on crystallization of the CZTS absorber and photovoltaic properties of Cu(Zn,Sn)(S,Se)2 solar cells

Nguyen

Ito

Dung

2015

Journal of Alloys and Compounds

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Temperature Dependence of Cu$_{2}$ZnSnS$_{4}$ Photovoltaic Cell Properties

Cited by 21 publications

References 11 publications

Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure

Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure

Atom-probe tomographic study of interfaces of Cu2ZnSnS4 photovoltaic cells

Effects of annealing conditions on crystallization of the CZTS absorber and photovoltaic properties of Cu(Zn,Sn)(S,Se)2 solar cells

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Temperature Dependence of Cu$_{2}$ZnSnS$_{4}$ Photovoltaic Cell Properties

Cited by 21 publications

References 11 publications

Improvement of the open-circuit voltage of Cu2ZnSnS4solar cells using a two-layer structure

Improvement of the open-circuit voltage of Cu2ZnSnS4solar cells using a two-layer structure

Atom-probe tomographic study of interfaces of Cu2ZnSnS4 photovoltaic cells

Effects of annealing conditions on crystallization of the CZTS absorber and photovoltaic properties of Cu(Zn,Sn)(S,Se)2 solar cells

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Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure

Improvement of the open-circuit voltage of Cu₂ZnSnS₄solar cells using a two-layer structure