Table 1. Specific surface area, porosity, and roughness factor of P25, HRT-1 and Dyesol-T materials.

Samples	Specific surface area (m2 g−1)	Porosity a) (%)	Roughness factor b) (μm−1)	Amount of dye c) (10−7 mol cm−2)
P25	42	34.9	118	2.4
HRT-1	67	56.6	125	2.7
Dyesol-T	74	64.2	103	3.4

^a)The porosities (P) of P25, HRT-1 and Dyesol-T were calculated according to: P = V_p/(ρ⁻¹ + V_p), where V_p is the specific cumulative pore volume (cm³ g⁻¹) and ρ is the density of TiO₂ (ρ = 4.3 g·cm⁻³)⁵⁰.

^b)An estimation of the roughness factor (R) per unit film thickness of the films is obtained by R = ρ (1 − P) S, where ρ is the density (g cm⁻³) of TiO₂, P is the porosity (%) of the film, and S is the specific surface area (m² g⁻¹)⁵¹.

^c)The dyed electrodes were soaked in a 0.4 M alkaline solution in methanol to desorb the dye from the electrodes. The amount of desorbed dye was quantified by measuring its optical absorption spectrum (Supplementary Fig. S6).