The Role of π Bridges in High‐Efficiency DSCs Based on Unsymmetrical Squaraines |
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Authors: | Dr Jared H Delcamp Dr Yanrong Shi Dr Jun‐Ho Yum Dr Tissa Sajoto Elisa Dell'Orto Dr Stephen Barlow Dr Mohammad K Nazeeruddin Prof Seth R Marder Prof Michael Grätzel |
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Institution: | 1. Laboratory for Photonics and Interfaces (LPI), Institution of Chemical Sciences and Engineering (ISIC), School of Basic Sciences, Swiss Federal Institute of Technology, CH‐1015 Lausanne (Switzerland), Fax: (+41)?21‐693‐41‐11;2. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332‐0400 (USA), Fax: (+01)?404‐894‐5909 |
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Abstract: | A series of squaraine‐based sensitizers with various π bridges and anchors were prepared and examined in dye‐sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4‐di‐n‐hexyl‐cyclopentadithiophene group that is directly attached onto the π bridge, JD10 , exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem‐di‐n‐hexyl substituents, which extend above and below the π‐conjugated dye plane. Dye JD10 demonstrates a power‐conversion efficiency of 7.3 % for liquid‐electrolyte dye‐sensitized solar cells and 7.9 % for cells that are co‐sensitized by another metal‐free dye, D35 , which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident‐photon‐to‐current‐conversion efficiency curve is realized for this dye with an excellent short‐circuit current of 18.0 mA cm?2. This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5 000 M ?1 cm?1 from 400 nm to the long‐wavelength onset of 724 nm for dye JD10 . |
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Keywords: | chromophores dyes/pigments photovoltaic cells sensitizers squaraines |
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