## 4 Conclusions  
In this work, we first investigated the differences between the optical properties of two dyes: a ruthenium complex, C106, and an organic donor-\(\pi\)-acceptor compound, Y123. The analysis of the absorption spectra shows that the Y123 photo-anode exhibits an absorption maximum peak at 485 nm, which, despite the highest molar extinction coefficient of this dye, has lower intensity values than those of the C106 photo-anode (401 and 541 nm). This evidence finds an explanation in the fact that C106 binds vertically to the TiO\({}_{2}\), with the bpy lying almost perpendicular to the TiO\({}_{2}\) surface, resulting as less sterically hindered, while the Y123 structure, more rigid and planar, binds vertically with a greater steric hindrance due to the presence of the lateral-OC\({}_{6}\)H\({}_{13}\) chains on the triphenylamine substituent. Moreover, we studied dyes' behavior when they were employed as sensitizers in a DSSC, focusing on several operating conditions, such as electrolyte composition, thickness of anode, and illumination environment. For this purpose, we performed measurements illuminating the cells both from the front and rear sides, discussing from a scientific point of view the change in electrical parameters. We achieved one of the highest bifaciality factors (BF) in the literature, of 93%, with C106 dye on a white background, to the best of our knowledge. This is important to highlight the great potential of a standard DSSC device when exploited in BIPV or in an indoor environment when the albedo effect can be present. We noticed an interesting effect concerning the devices' performances related to the TiO\({}_{2}\) thickness. C106 dye has a great absorption capacity, as seen from absorbance spectra, and its PCE trend is not significantly influenced by TiO\({}_{2}\) thickness. On the other hand, the organic dye, Y123, with a lower absorbance, is positively affected by TiO\({}_{2}\) thickness, increasing the PCE. Furthermore, when the albedo's effect was exploited, Y123 and C106 achieved PCE values of 12.8% and 10.3%, respectively.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **PCE (\%)** & **Jsc (mA/cm\({}^{2}\))** & **Voc (Volt)** & **FF (\%)** \\ \hline B\_C106 & 5.90 & 12.20 & 0.72 & 61 \\ \hline W\_C106 & 10.28 & 22.69 & 0.71 & 63 \\ \hline B\_Y123 & 6.34 & 12.50 & 0.70 & 70 \\ \hline W\_Y123 & 12.78 & 26.68 & 0.77 & 62 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Electrical parameters of J–V curves of C106 and Y123 devices (TiO\({}_{2}\) film thickness of 11.6 \(\upmu\)m) on white and black background.  
Figure 5: J–V of C106 and Y123 devices (TiO\({}_{2}\) film thickness of 11.6 \(\upmu\)m) on white and black background.  
**Author Contributions:** Conceptualization, J.B., S.G. and G.C.; formal analysis, J.B., S.G. and G.C.; investigation, J.B., S.G., A.C. and G.C.; resources, G.D.M., F.M. and G.C.; funding acquisition, G.D.M. and G.C.; methodology, J.B. and G.C.; visualization, J.B. and G.C.; data curation, J.B., S.G., A.C. and G.C.; writing--original draft preparation, J.B., S.G. and G.C.; writing--review and editing, J.B., S.G., F.M. and G.C.; supervision, J.B. and G.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The authors gratefully acknowledge the project Best4U--\"Tecnologia per celle solari bifacciali ad lata Efficionza a 4 terminali per utility scale\".  
**Institutional Review Board Statement:** Not Applicable.  
**Informed Consent Statement:** Not Applicable.  
**Data Availability Statement:** Not Applicable.  
**Acknowledgments:** We acknowledge the technical support by [PERSON], [PERSON], and [PERSON] for the electronic and mechanical apparatus used in the experiments.  
**Conflicts of Interest:** The authors declare no conflict of interest.