Demonstration of 12 Years Outdoor Working of Highly Durable Dye-Sensitized Solar Cell Modules Employing Hydrophobic Surface Passivation and Suppression of Biased Distribution of Iodine Ions

Dye-sensitized solar cells (DSCs) outperform conventional silicon solar cells in terms of weight and design flexibility. Therefore, besides standard rooftop installation, DSCs are suitable for new applications, including windows and walls. However, insufficient durability remains a critical issue, and outdoor working over 10 years is yet to be realized. In this study, we developed two approaches to improve the durability. The first involves hydrophobic surface passivation on the TiO2 surfaces by adopting alkylbenzimidazole (CnH2n+1BI) with long alkyl chains instead of the conventional additive (N-methylbenzimidazole) used for high open-circuit voltage in an ionic liquid-based electrolyte. The additive with a suitable alkyl-chain length (N-butylbenzimidazole and N-hexylbenzimidazole) notably improved the resistance against infiltrating water. The second approach refers to the DSC module arrangement. A unique problem of large sized modules is that the I3- distribution often becomes biased over time, lowering the conversion efficiency. Horizontal module arrangements and/or the strip-shaped single cells in the modules solved this problem. By adopting these two approaches, we have demonstrated that the 10 cm x 11 cm-sized DSC modules have high durability to maintain 75% of their initial performance after the 12 year outdoor working test. This is the longest demonstrated lifetime for DSC modules outdoors.