Organic sensitizers possessing carbazole donor and indeno[1,2-b] thiophene spacer for efficient dye sensitized solar cells

• Organic dyes for sensitized solar cells.
• Organic dyes consisting the carbazole moiety.
• Comparative analysis between iodine vs cobalt electrolyte.
• Chenodeoxycholic acid as a co-absorbent.
• Solar cell with highest conversion efficiency 6.66%.

Three organic sensitizers consisting of carbazole as an electron donor, indeno[1,2-b]thiophene as the bridging unit have been synthesized and characterized for use in dye-sensitized solar cells. Time-dependent density functional theory studies are indicated that large intramolecular charge transfer takes place from the highest occupied molecular orbital to the lowest unoccupied molecular orbital though the donor is twisted (∼50°) with respect to the π-linker. However, the introduction of indeno[1,2-b]thiophene as a planar π-linker unit is presumed to be the reason for a strong molar absorption coefficient and a red-shifted absorption band. Air mass 1.5 global illumination (100 mW cm−2), the 3-(5-(6-(3,6-bis(2,4-bis(hexyloxy)phenyl)-9H-carbazol-9-yl)-4,4-dimethyl-4H-indeno[1,2-b]thiophen-2-yl)thioph-2-yl)-2-cyanoacrylic acid based device displayed the best performance: an open-circuit voltage of 826 mV, a short-circuit current density of 9.16 mA cm−2, a fill factor of 0.777, and an overall conversion efficiency of 5.88%. Upon changing the electrolyte from iodine to cobalt electrolyte, 3-(5-(6-(3,6-bis(2,4-bis(hexyloxy)phenyl)-9H-carbazol-9-yl)-4,4-dimethyl-4H-indeno[1,2-b]thiophen-2-yl)thioph-2-yl)-2-cyanoacrylic acid based dye-sensitized solar cells gave the remarkably improved overall conversion efficiency (6.66%), which is one of the highest values based on carbazole sensitizers.

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