Stage | Description |
Stage #1 | The incident light (photon) is absorbed via a photosensitizer, and therefore, due to the photon absorption, electrons get promoted from the ground state (S+/S) to the excited state (S+/S*) of the dye, where the absorption for most of the dye is in the domain of 700 nm which corresponds to the photon energy almost about 1.72 eV. |
Stage #2 | The excited electrons with a lifetime of nanosecond span are injected into the conduction band of nanoporous TiO2 electrode which lies below the excited state of the dye, where the TiO2 absorbs a small fraction of the solar photons from the UV region [43] . Consequently, the dye gets oxidized. (1) (2) |
Stage #3 | Such injected electrons are transported among TiO2 nanoparticles and diffuse towards the back contact (transparent conducting oxide [TCO]). Via the external circuit, electrons attain the CE. |
Stage #4 | The electrons at the CE reduce to I−; therefore, dye regeneration or the regeneration of the ground state of the dye occurs thanks to the acceptance of electrons from I− ion redox mediator, and I− gets oxidized to (oxidized state). (3) |
Stage #5 | Plus, the oxidized mediator ( ) diffuses towards the CE and reduces to I ion. (4) |