“…Hence, the V OC is enhanced either by (i) upshift of E CB or by (ii) downshift of W redox (this means by enhancement of the mediator's redox potential in the electrochemical scale). In the first case, the available shifts in band energetics are limited to tens to hundreds of meV through engineering of the TiO 2 structure [18] or by electrolyte additives [9,10] but the engineering of the mediator's W redox is theoretically limited only by the electrochemical potential of the dye's ground state, which is usually near 1 V vs. SHE. However, small overpotential (≈ 0.1 to 0.2 V) is needed as a driving force for dye regeneration [7,9,10,19].…”