Working mechanisms of PECs and OPVs

While for a solar water splitting cell, light is directly absorbed by the semiconductor electrode (anode or cathode). The separation of electron-hole pairs is achieved in the built-in electric field near the semiconductor surface. The electric field is formed due to the charge transfer between the semiconductor electrode and the electrolyte as schematically shown in Fig. 17.5(b) [28]. Take an n-type semiconductor electrode for example 

HOMO = highest occupied molecular orbital (valence band) 

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