The phase transfer can be easily monitored by the color change of toluene (black to colorless) and FA (yellow to black) phases. Black-colored colloidal dispersion of CZTSe NCs capped with organic ligand undergoes the phase transfer from toluene to FA with the inorganic ligand of (NH4)2S in FA upon exchange of the original organic surface ligand with S2−. Figure 2 FTIR spectra of OLA and CZTSe NCs before and after ligand exchange. The inset shows the colloidal dispersion

of CZTSe NCs before and after Pexidartinib mw ligand exchange. Figure 3a shows the XRD patterns of CZTSe NC thin films before and after 550°C selenization for 30 min. CZTSe NC thin films were prepared by the dip-coating method. CZTSe NCs were dipped and dried on a silicon substrate from perchlorethylene before ligand exchange and aqueous dispersions after ligand exchange. All the diffraction peaks in the XRD pattern appear at 27.3°, 45.3°, 53.6°, 66.3°, and 72.8°, consistent with the (112), (220/204), (312), (400/008), anti-PD-1 monoclonal antibody and (316) planes, respectively, which match those of tetragonal-phase CTZSe (JCPDS 52-0868). These results confirmed that the ligand exchange does not change the structure of CZTSe NCs. The full width at half maximum (FWHM) of the (112)

peak before and after ligand exchange is 0.733° and 0.696°, respectively, while the value decreases to 0.222° and 0.120°, respectively, by selenization, indicating a high-quality crystalline structure [29]. From Figure 3a, we can see that the intensity of the diffraction peaks increased largely by selenization after ligand exchange and the FWHM of the (112) peak after ligand exchange was less than that before ligand exchange, indicating the improvement of the crystallinity. XRD patterns show the improvement of the crystallinity after ligand exchange benefits from the removal of the large organic molecules [29]. Figure 3 XRD patterns (a) and Raman spectra (b) of CZTSe nanocrystal thin films before and after 550°C selenization.

Herein, Raman spectroscopy was further employed for phase analysis, as shown in Figure 3b. Because (NH4)2S is used during ligand exchange, the CZTSe Depsipeptide manufacturer nanocrystal thin film shows one weak peak of Cu2ZnSnS4 at around 333 cm−1 after ligand exchange. There are no characteristic peaks of other impurities detected. CZTSe thin films prepared by selenization shows three peaks of CZTSe with Raman shift at 172, 192, and 232 cm−1, in agreement with previous reports [30]. These results further confirmed that the ligand exchange did not change the structure of CZTSe NCs. There are no observable secondary phases such as Cu2Se, SnSe, and Cu2SnSe3. The intensity of the Raman peaks increased largely after annealing due to the recrystallization of CZTSe NCs. The resistivity (ρ) of CZTSe NC thin films by selenization is listed in Table 1. The resistivity of CZTSe NC thin films before and after ligand exchange is 3.