Alkyl effects on charge recombination in copper electrolyte-based dye-sensitized solar cells: Insights for targeted...

Two quinoxaline dyes utilized in copper-electrolyte-based dye-sensitized solar cells (Cu-DSSCs) are theoretically investigated to analyze the impact of alkyl chains on dye performance. The investigation shows that ZS4, known for its record efficiency of up to 13.2 %, exhibits higher electron coupling and fewer binding sites for dye-[Cu(tmby)₂]²⁺ interaction compared to ZS5. Contrary to common belief, alkyl chains are found to not only provide shielding but also hinder the interaction between dye and [Cu(tmby)₂]²⁺ by influencing the optimal conformation of dyes, thereby impeding the charge recombination process. It is crucial to consider the influence of alkyl chains on dye conformation when discussing the relationship between dye structure and performance, rather than oversimplifying it as often done traditionally. Building on these findings, eight dyes are strategically designed by adjusting the position of the alkyl chain to further decrease charge recombination compared to ZS4. Theoretical evaluation of these dyes reveals that changing the alkyl chain on the nitrogen atom from 2-ethylhexyl (ZS4) to 1-hexylheptyl (D3-2) not only reduces the charge recombination rate but also enhances light harvesting ability. Therefore, D3-2 shows potential as a candidate for experimental synthesis of high-performance Cu-DSSCs with improved efficiency.