Figure 4

(a) The VB XPS spectra of porous-ZnO, CuPc and porous-ZnO:1% CuPc. Inset: The straight solid lines show the linear regions and the VBM can be determined by the intersections of the lines with the baselines. (b) The parts of VB XPS spectra of the porous-ZnO modified with different amount of CuPc. (c) Absorbance squared versus photon energy for porous-ZnO, CuPc and porous-ZnO:1% CuPc, respectively. The straight solid lines show the linear regions and the band gaps can be determined by the intersections of the lines with the horizontal axis. (d) Schematic showing the process of the photogenerated-electron transfer from the ZnO-CuPc composite to the adjacent porous-ZnO under 570-nm illumination. The black dots represent electrons.