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The Role of π Bridges in High‐Efficiency DSCs Based on Unsymmetrical Squaraines
Author(s) -
Delcamp Jared H.,
Shi Yanrong,
Yum JunHo,
Sajoto Tissa,
Dell'Orto Elisa,
Barlow Stephen,
Nazeeruddin Mohammad K.,
Marder Seth R.,
Grätzel Michael
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201202677
Subject(s) - dye sensitized solar cell , molar absorptivity , energy conversion efficiency , photochemistry , conjugated system , electrolyte , delocalized electron , chemistry , homo/lumo , materials science , optoelectronics , molecule , electrode , organic chemistry , optics , polymer , physics
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 .