Photoelectrochemical Photocurrent Switching and Related Phenomena
‘In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before.’
‘But in poetry, it is the exact opposite.’
6.1 Photocurrent Generation and Switching in Neat Semiconductors
Organic and inorganic semiconducting materials generate photocurrent upon illumination with light of appropriate energy due to the Dember effect. Photoelectrochemical properties are usually studied in a three-electrode setup with the semiconducting material in contact with an electrolyte. In typical cases the polarity of the photocurrent depends on the conductivity type: n-type semiconductors generate anodic photocurrent (i.e. electrons are collected by the conducting support, while holes oxidize some components of the electrolyte), while with p-type semiconductors it is cathodic (Figure 6.1a, b). The latter case requires a sacrificial electron acceptor to be present in the electrolyte. These processes are utilized in dye-sensitized solar cells, where the electrolyte contains a reversible redox couple (iodide/triiodide is the most common) [1, 2].
Efficient charge separation is driven by the electric field within the semiconductor crystal. Therefore band bending in the electrolyte–semiconductor ...