Unsymmetrical squaraine sensitizers containing auxiliary arylamine donor for NIR-harvesting on dye-sensitized solar cell

• We develop three new squaraine dyes for DSSC.
• Auxiliary arylamine donor brings bathochromic shift of the absorption band.
• Auxiliary arylamine donor hinders electron recombination.
• A power conversion efficiency of 3.39% was achieved for the DSSC based on WH-SQ03.

Developing sensitizers capable of absorbing light intensely in the red to near-IR region is important to improve the performance of dye-sensitized solar cells. In this article, three new squaraine sensitizers containing diarylamines with varied alkyl or alkoxyl chain substituents as auxiliary donors were synthesized and utilized. The effects of different donor tail chains, i.e., methyl, methoxyl and hexyloxy groups on the photophysical, electrochemical and photovoltaic properties were investigated. Results indicated the alkoxyl chains brought about a more broadened photoresponse than the alkyl chain and the long hydrocarbon chain was superior to short chains in suppression of electron recombination. Therefore, with a bis(4-(hexyloxy) phenyl) amine substituent, a squaraine sensitized solar cell presented expansion of the incident photon-to-current conversion from the red to near infrared wavelength region up to 800 nm and hindered electron recombination, resulting in an efficiency of 3.39% under AM 1.5 irradiation.

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