Review of the Development of Dyes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have attracted considerable attention over the last 25 years owing to their potential for the low-cost conversion of photovoltaic energy. The most important DSSC component is the sensitizer dye, which is largely responsible for light harvesting and charge separation. Although tremendous research efforts have been focused on dye development, many challenges remain and a deeper understanding of the design rules for DSSC sensitizers is required to obtain efficient and long-term stable DSSCs. State-of-the-art DSSCs based on single sensitizers have reached power conversion efficiencies (PCEs) of >11.5 % for ruthenium dyes, >13 % for porphyrin dyes, and >14 % for metal-free organic dyes. However, the highest efficiency officially recognized by the National Renewable Energy Laboratory is only 11.9 %, achieved by the Sharp Co., Japan, in 2013. Furthermore, there has been a lack of significant milestones in active commercialization, particularly with respect to exploiting the near-infrared region for higher PCEs and greater device durability. While ruthenium-based dyes have some disadvantages for practical application in DSSCs, both porphyrin and metal-free organic dyes have attracted considerable interest. In this review, we summarize recent progress in the rational design of ruthenium dyes, porphyrin dyes, metal-free organic dyes, and natural dyes for use in DSSCs.