Effect of Co-Solvent Percentages on the Exfoliation Rate of NiTe2 Thin Film for Transparent Electrodes

Abstract

We attempted to maximize the transmittance of 2D NiTe2 thin film using the liquid-phase exfoliation (LPE) process to confirm the applicability of NiTe2 as a transparent electrode. The LPE process, using a co-solvent of organic solvent and water, is a stable and efficient method of increasing transmittance at low cost. In this report, the effect of 12 different co-solvents, mixtures of acetone, ethanol, isopropyl alcohol, and water, on exfoliation rate was studied. NiTe2 thin film with a thickness of 6.3 nm prepared by sputtering, and exhibited a highest transmittance of 68% and a lowest resistivity of 291 μΩ·cm after 12 hrs sonication in ethanol/water co-solvent (ethanol : water = 60 : 40 vol. %). Three physical properties, polarization and dispersion ratio (p/d ratio), boiling point, and water contents, were compared to determine which property was the main control factor for the LPE process. Unlike previous LPE processes for powders of 2D materials, it was revealed that the improvement in the transmittance of the NiTe2 thin film was more strongly dependent on both of vol.% of water and boiling point of the solvents. This was because the transmittance improved after removing the NiTe2 thin film from the substrate, rather than layer by layer exfoliation. We believe that NiTe2 thin film prepared by sputtering followed by exfoliation process can be one of the potential candidates for transparent electrode.