Microstructural analysis of 9.7% efficient Cu2ZnSnSe4 thin film solar cells

Buffière, Marie; Brammertz, Guy; Batuk, Maria; Verbist, Christophe; Mangin, Denis; Köble, Ch.; Hadermann, Joke; Meuris, Marc; Poortmans, Jef

doi:10.1063/1.4901401

Cited by 24 publications

(25 citation statements)

References 22 publications

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“…It can be seen that after only 2 min of treatment, the Cu content drops from 10 at.% to less than 1 at.%. Similar evolution was observed for the Zn content which was found to decrease from about 25 at.% (the relatively high initial Zn content being due to the presence of ZnSe secondary phase at the surface of the samples) 23 to 10 at.%. 23 In the meantime, the Sn content drastically increases (from 9 at.% to 22 at.%) accompanied by a shift to higher binding energies of the Sn XPS peak indicating the formation of a Sn-based secondary phase.…”

Section: Cztse Layers Treated In Liquid Phase Ammonium Sulfidesupporting

confidence: 77%

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

et al. 2017

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In this contribution, we report on the impact of ammonium sulfide ((NH4)2Sx) chemical treatments done at room temperature on the surface properties of Cu2ZnSnSe4 (CZTSe) thin film. The first approach is based on the immersion of the absorber layer in a (NH4)2Sx solution (20 wt.%). This method results in the preferential etching of Se, Sn and Zn atoms from the absorber surface. After a treatment time of 1 minute, the performances of the solar cells are found to be improved. The second approach consists in the exposure of the CZTSe layer to ammonium sulfide vapors. In this case, it was found that the progressive sulfurization of the surface of absorber lead to the decomposition of the CZTSe phase into Sn(S,Se)x and Se 0 secondary phases. As a consequence, the short circuit current of the corresponding solar cells is reduced. Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films AbstractIn this contribution, we report on the impact of ammonium sulfide ((NH4)2Sx) chemical treatments done at room temperature on the surface properties of Cu2ZnSnSe4 (CZTSe) thin film. The first approach is based on the immersion of the absorber layer in a (NH4)2Sx solution (20 wt.%). This method results in the preferential etching of Se, Sn and Zn atoms from the absorber surface. After a

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Section: Cztse Layers Treated In Liquid Phase Ammonium Sulfidesupporting

confidence: 77%

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

et al. 2017

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“…Furthermore, it can be seen in Figure 7 that voids are present in the CZTSe layer and Cu and Zn rich secondary phases, possibly ZnSe and Cu x Se y , are segregated inside them as commonly observed. 6,38 In both non-annealed as well as annealed sample there are evidences for regions with enhanced Sn and O signal near the voids, suggesting the presents of SnOx, however different to recent auger nanoprobe studies of air annealed CZTSSe absorbers no SnOx is found in the grain boundaries. 9 The highest cell efficency achieved with the combination of KMnO 4 +H 2 SO 4 and Na 2 S etching together with a optimal full cell post deposition annealing treatment of 35 minutes at 200ºC is 8.3% as shown in Figure 7 which was below 3% before post deposition annealing.…”

Section: Influence Of Annealing Treatment On Cztse Bulkmentioning

confidence: 72%

Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices

et al. 2015

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A detailed study explaining the beneficial effects of low temperature post deposition annealing combined with selective surface etchings for Cu 2 ZnSnSe 4 (CZTSe) based solar cells is presented. After performing a selective oxidizing surface etching to remove ZnSe secondary phases typically formed during the synthesis processes an additional 200ºC annealing step is necessary to increase device performance from below 3% power conversion efficiency up to 8.3% for the best case. This significant increase in efficiency can be explained by changes in the surface chemistry which results in strong improvement of the CdS/CZTSe heterojunction commonly used in this kind of absorber/buffer/window heterojunction solar cells. XPS measurements reveal that the 200ºC annealing promotes a Cu depletion and Zn enrichment of the etched CZTSe absorber surface relative to the CZTSe bulk. Raman measurements confirm a change in Cu/Zn ordering and increase in defect density. Furthermore, TEM microstructural investigations indicate a change of grain boundaries composition by a reduction of their Cu content after the 200ºC annealing treatment. Additionally, insights in the CdS/CZTSe interface are gained showing a significant amount of Cu in the CdS buffer layer which further helps the formation of a Cu-depleted surface and seems to play an important role in the formation of the pn-heterojunction.

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“…Buffière et al . suggested that up to a 40‐nm diameter the ZnSe phase is located near the back contact, and smaller ZnSe phases are segregated at the grain boundaries and near the grains . The Cu‐rich spots and ZnSe phases have a tendency to decompose into the CZTSe phase .…”

Section: Resultsmentioning

confidence: 99%

Enhancement of photo‐conversion efficiency in Cu₂ZnSn(S,Se)₄ thin‐film solar cells by control of ZnS precursor‐layer thickness

Kim

Son

Nguyen

et al. 2015

Progress in Photovoltaics

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CZTSSe thin-film absorbers were grown by stacked ZnS/SnS/Cu sputtering with compound targets, and the precursors were annealed in a furnace with a Se atmosphere. We controlled the thickness of the ZnS precursor layer for the CZTSSe thin films in order to reduce the secondary phases and to improve the performance of the devices. The optimal value of the ZnS precursor thickness was determined for the CZTSSe absorbers, and this configuration showed an efficiency of up to 9.1%. In this study, we investigated the depth profiles of the samples in order to determine the presence of secondary phases in the CZTSSe thin films by Raman spectroscopy and Kelvin probe force microscopy. Cu 2 SnSe 3 , ZnSe, and MoSe 2 secondary phases appeared near the back contact, and the work function distribution of the CZTSSe thin-film surface and the secondary phase distribution were different depending on the depths of the absorber layer. This phase characterization allows us to describe the effects that changes in the thickness of the ZnS precursor can have on the performance of the CZTSSe thin-film solar cells. Although it is important to identify the phases, the effects of secondary phases and point defects are not yet fully understood, even in optimal devices. Therefore, phase identification that is based on the work function and the results obtained from the Raman spectra in terms of the depth profile are instrumental to improve the surface and interface of CZTSSe thin-film solar cells.

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Microstructural analysis of 9.7% efficient Cu2ZnSnSe4 thin film solar cells

Cited by 24 publications

References 22 publications

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices

Enhancement of photo‐conversion efficiency in Cu₂ZnSn(S,Se)₄ thin‐film solar cells by control of ZnS precursor‐layer thickness

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Microstructural analysis of 9.7% efficient Cu2ZnSnSe4 thin film solar cells

Cited by 24 publications

References 22 publications

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

Effect of ammonium sulfide treatments on the surface properties of Cu2ZnSnSe4 thin films

Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices

Enhancement of photo‐conversion efficiency in Cu2ZnSn(S,Se)4 thin‐film solar cells by control of ZnS precursor‐layer thickness

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Enhancement of photo‐conversion efficiency in Cu₂ZnSn(S,Se)₄ thin‐film solar cells by control of ZnS precursor‐layer thickness