## 3 Results and Discussion
### Bifacial Study on Two Different Electrolytes and Dyes
#### 3.2.2 The Bifacial Factor  
In the case of front-side irradiation, the electron path in the TiO\({}_{2}\) conduction band is shorter, and the hole path in the electrolyte, which span from the reduced dye to the platinum counter electrode, is longer in comparison to those for the case of rear-side irradiation. This effect can reduce the difference between the conversion efficiencies for front- and rear-side irradiation, resulting in high performance and enabling cost-effective application in large-scale solar power generation systems [42]. On the other hand, in the case of rear-side irradiation, the incident light is filtered by the iodide electrolyte [43], resulting in blocking the blue-light region and passing the red-light region. All rear-side measured devices show an increment in FF. From the rear side, fewer photons can reach the sensitized TiO\({}_{2}\), due to the platinum/electrolyte as middle layers that can absorb part of the photons. A minor number of photons reaching the sensitized TiO\({}_{2}\) leads to a more efficient electron injection and less charge recombination, which results in a FF increment.  
All measured cell on a white background show better results in comparison to the respective measurement on a dark one. Indeed, the white background works as a scattering layer that can amplify the light effect, thus more photons can reach the device. Consequently, a current increment is observed on measured devices on white background. In the column \"bifaciality factor\" in Table 1, the ratio of each measured cell from the rear to the front side is reported for each dye, electrolyte, and background. With a black background, the BF is lower than the respective cell in the white one. A maximum BF of 93% has been obtained with C106 dye, J8* electrolyte, and a white background.  
Considering the results in Table 1, it is possible to notice that BF is influenced by the electrolyte and by the dye. J8-electrolyte-based devices have a BF higher than HSE-based ones, and this depends on the different viscosity of the employed solvents. As discussed previously, J8 solvent allows a faster regeneration of the redox couple, and this bringsbetter performances in the rear side also. Analyzing BF differences for both electrolytes, we notice that the most influenced parameter is the current density; indeed, considering HSE-C106 device from rear to front, the current doubles (from 6.42 to 11.99 mA/cm\({}^{2}\)), different to the case of J8-C106, where Jsc increment is less evident (from 9.62 to 13.94 mA/cm\({}^{2}\)). A BF of 93% was achieved due to the exploitation of the albedo effect with C106 on a white background: more scattered photons and less differences between Jsc from rear to front (from 19.34 to 21.07 mA/cm\({}^{2}\)). It is worth highlighting that exploiting the albedo effect, a standard DSSC cell reached the bifaciality factor of 93%, and this is mandatory to understand the great potential of this technology when used as BIPV in windows or indoor environment, even with different angle inclinations.  
C106 has a higher BF than Y123 (and therefore less differences between front- and rear-side measurements) and it is possible to find the explanation when observing their absorbance spectra (Figure 2b). A sensitized C106 dye in a TiO\({}_{2}\) surface shows two maximum peaks at 401 and 541 nm. Iodine/iodide electrolyte absorbs from 300 to 400 nm [44]; therefore, in the rear side, when the electrolyte first filters the light, this cannot block the C106 excitation in the second band at 540 nm. On the other hand, Y123 has one absorption band from 400 to 500 nm, partially influenced by the filtered light from the electrolyte; from the rear side, this probably leads to higher PCE differences from front to rear for Y123 dye than for C106 dye.