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Secondary Phase Formation Mechanism in the Mo-Back Contact Region during Sulfo-Selenization Using a Metal Precursor: Effect of Wettability between a Liquid Metal and Substrate on Secondary Phase Formation
- Secondary Phase Formation Mechanism in the Mo-Back Contact Region during Sulfo-Selenization Using a Metal Precursor: Effect of Wettability between a Liquid Metal and Substrate on Secondary Phase Formation
- Kim, Se-Yun; Kim, Seung-Hyun; Hong, Sanghun; Son, Dae-Ho; Kim, Young-ill; Kim, Sammi; Ahn, Kwangseok; Yang, Kee-Jeong; Kim, Dae-Hwan; Kang, Jin-Kyu
- DGIST Authors
- Son, Dae-Ho; Yang, Kee-Jeong; Kim, Dae-Hwan; Kang, Jin-Kyu
- Issue Date
- ACS Applied Materials and Interfaces, 11(26), 23160-23167
- Article Type
- Author Keywords
- CZTSSe; metal precursor; Mo back contact; secondary phase formation mechanism; wettability
- ZNO INTERMEDIATE LAYER; CU2ZNSNS4 SOLAR-CELLS; THIN-FILMS; SULFURIZATION; ABSORBER
- Recently, highly efficient CZTS solar cells using pure metal precursors have been reported, and our group created a cell with 12.6% efficiency, which is equivalent to the long-lasting world record of IBM. In this study, we report a new secondary phase formation mechanism in the back contact interface. Previously, CZTSSe decomposition with Mo has been proposed to explain the secondary phase and void formation in the Mo-back contact region. In our sulfo-selenization system, the formation of voids and secondary phases is well explained by the unique wetting properties of Mo and the liquid metal above the peritectic reaction (?-Cu6Sn5 → ϵ-Cu3Sn + liquid Sn) temperature. Good wetting between the liquid Sn and the Mo substrate was observed because of strong metallic bonding between the liquid metal and Mo layer. Thus, some ϵ-Cu3Sn and liquid Sn likely remained on the Mo layer during the sulfo-selenization process, and Cu-SSe and Cu-Sn-SSe phases formed on the Mo side. When bare soda lime glass (SLG) was used as a substrate, nonwetting adhesion was observed because of weak van der Walls interactions between the liquid metal and substrate. The Cu-Sn alloy did not remain on the SLG surface, and Cu-SSe and Cu-Sn-SSe phases were not observed after the final sulfo-selenization process. Additionally, Mo/SLG substrates coated with a thin Al2O3 layer (1-5 nm) were used to control secondary phase formation by changing the wetting properties between Mo and the liquid metal. A 1 nm Al2O3 layer was enough to control secondary phase formation at the CZTSSe/Mo and void/Mo interfaces, and a 2 nm Al2O3 layer was enough to perfectly control secondary phase formation at the Mo interface and Mo-SSe formation. © 2019 American Chemical Society.
- American Chemical Society
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- Division of Energy Technology1. Journal Articles
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