Dendritic-based co-adsorbents for dye-sensitized solar cells: Effect of the generations and alkyl chain lengths

Series of dendritic building blocks (G series) with various periphery alkyl chain lengths (C3, C10 and C18) were prepared via convergent synthesis route through reaction-selective building block, (4-Isocyanato-4′(3,3-dimethyl-2,4-dioxo-azetidino)diphenylmethane, IDD) and diethylenetriamine (DETA) via alternative addition and ring-opening reaction. These azetidine-2,4-dione containing dendritic building blocks then reacted with several amino acid compounds to generate the corresponding dendritic co-adsorbents (GA series). GA series comprising different generations, various alkyl chain lengths closed to anchor and/or in the periphery are discussed and applied into dye-sensitized solar cells (DSSCs). The cells utilized similar phenothiazine-based dyes (HL5) as sensitizer with fixed concentration (0.3 mM) of co-adsorbents are fabricated to explore the effect on cell performances and interfacial charge properties. Power conversion efficiencies (PCEs) of 7.02–7.76% were achieved, which better than the commercially available CDCA co-adsorbent based cell (6.71% ± 0.14%). In addition, the highest conversion efficiency also reaches 95% of the standard cell based on N719 metal dye. Herein, several observations: (1) under various alkyl chain lengths closed to anchor, the longest one has efficient charge recombination; (2) under various alkyl chain lengths in the periphery, the moderate one has the best interfacial properties with the longest electron lifetime value; (3) under different generations, the largest one can reduce dye aggregation and charge recombination significantly. Based on our pervious initial study on dendritic co-adsorbents, we further investigated several molecular design on dendritic co-adsorbents to realize the structural effect on cell performance that might be useful for DSSC applications.