• The adsorbed dye
molecule absorbs a
photon forming an
excited state. [dye*]
• The excited state of the
dye can be thought of
as an electron-hole
pair (exciton).
• The excited dye transfers an electron to the semiconducting TiO
2
(electron
injection). This separates the electron-hole pair leaving the hole on the
dye. [dye*
+
]
• The hole is filled by an electron from an iodide ion.
[2dye*
+
+ 3I
-
2dye + I
3
-
]
Theory