Nanostructured Semiconductor Materials for Dye-Sensitized Solar Cells

Figure 9

Mechanisms of photoactivated CO₂ reduction on a -type semiconductor electrode: (a) heterogeneous photoelectrocatalysis occurring directly at the semiconductor electrode; (b) homogeneous catalysis mediated by a molecular catalyst in the electrolyte; (c) heterogeneous photoelectrocatalysis directly on a metal-decorated semiconductor electrode; (d) heterogeneous catalysis mediated by a molecular catalyst anchored on the semiconductor electrode. In all four examples, photoexcitation occurs at the semiconducting cathode. , , and indicate the upper edge of the semiconductor valence band (VB), the lower edge of the semiconductor conduction band (CB), and the Fermi level of the -type semiconductor, respectively. The illuminated electrode is reverse biased in these four examples, adapted from [282].

(a)

(b)

(c)

(d)