New Insight of Li-Doped Cu2ZnSn(S,Se)4 Thin Films: Li-Induced Na Diffusion from Soda Lime Glass by a Cation-Exchange Reaction
2017
Yang, Yanchun | Tianhang, | Pan, Daocheng
In our recent report (ACS Appl. Mater. Interfaces 2016, 8, 5308), Li⁺ ions had been successfully incorporated into the lattice of the selenized Cu₂ZnSn(S,Se)₄ thin film on a quartz substrate by substituting equivalent Cu⁺ ions, and Li⁺ ions was also found to have the little effect on the crystal growth and defect passivation. To further improve the cell performance of Li-doped CZTSSe devices, we conducted the same experiments on the sodium-rich soda-lime glass (SLG) substrate in this study, instead of sodium-free quartz substrate. Surprisingly, only trace amounts of Li (Li/Cu molar ratio ∼1 × 10–⁴) were detected in the final CZTSSe thin films; meanwhile, a large amount of sodium was present on the surface and at the grain boundaries of the selenized thin films. A Li/Na exchange mechanism is used to explain this phenomenon. Only on the sodium-free substrate can Li⁺ ions enter the CZTSSe host lattice, and doping Li⁺ ions on the SLG substrate are nearly identical to doping Na⁺ ions.
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