The Effect of Solvent Mixing Ratios on the Exfoliation of 2D NiTe 2 Thin Films for Transparent Electrodes

NiTe 2 thin films have been considered promising candidates for transparent electrodes due to their high electrical conductivity and 2-dimensional (2D) layered structure. The transparency of 2D thin films with layered structure can be further improved by the exfoliation process. In the process, the increase in electrical resistance should be minimized by maintaining electrical continuity in the thin film. In this study, the mixing ratio of ethanol, acetone, and DI water in the solvent for the liquid-phase exfoliation (LPE) process was optimized to achieve high transmittance while suppressing the increase in electrical resistance. We prepared three solvents by varying the mixing ratio (ethanol:acetone:DI water = 2:4:4, 3:3:4, and 4:2:4). In the three mixed solvents, NiTe 2 thin films were removed by two mechanisms: separation from the substrate and layer-by-layer exfoliation. Some of the NiTe 2 grains were separated from the glass substrate in the early stage of the LPE process, and layer-by-layer exfoliation became the major mechanism when LPE proceeded longer than 6 h in the three solvents. Among the three solvents, the one with a 3:3:4 ratio more effectively suppressed the increase in electrical resistance during the separation of the NiTe 2 thin film. The separation of NiTe 2 grains provided an advantageous condition for layer-by-layer exfoliation. Additionally, the similarity of the polarization and dispersion ratio of 3-3-4 with the one of NiTe 2 accelerated layer-by-layer exfoliation. The optimized solvent of 3-3-4 improved the transmittance of the NiTe 2 thin film from 59.6% to 68.4% after the 8-h LPE process. Graphic Abstract