Fig. 1. (Color online) (a) Schematic illustration of one-pot synthesis of CZTS nanocrystals. XRD patterns of CZTS nanocrystals obtained at (b) low Cu content, (c) high Cu content. (d) TEM images of hexagonal wurtzite CZTS. The inset is an enlarged view. (e) SAED pattern of hexagonal wurtzite CZTS. (f) HRTEM images of hexagonal wurtzite CZTS nanocrystals in (002) crystal plane and (g) in (101) crystal plane.

Fig. 2. (Color online) (a) SEM-EDS element distribution diagram of hexagonal wurtzite CZTS nanocrystals. (b) The cation percentages of CTZS nanocrystals obtained from EDS results. XPS signals of (c) Cu, (d) Sn, (e) Zn, and (f) S elements in hexagonal wurtzite CZTS nanocrystals.

Fig. 3. (Color online) (a) Diffuse reflectance spectra and (b) the plots of (αhv)² versus the photon energy of CZTS nanocrystals with different Cu content. UPS spectra of (c) high-binding energy secondary-electron cutoff and (d) valence-band edge regions of hexagonal wurtzite CZTS nanocrystals. (e) Energy level structure diagram of hexagonal wurtzite CZTS nanocrystals.

Fig. 4. (Color online) (a) Photocurrent of CZTS nanocrystals with different Cu content. (b) Impedance spectra of CZTS nanocrystals with different Cu content. (c) Photocatalytic hydrogen evolution for hydrogen amount variation with time. (d) Photocatalytic hydrogen production rates.

Table 1. Summary of the energy level information of wurtzite CZTS nanocrystals.