A study of dye anchoring points in half-squarylium dyes for dye-sensitized solar cells

Connell, A., Holliman, P.J., Davies, M.L., Gwenin, C.D., Weiss, S., Pitak, M.B., Horton, P.N., Coles, S.J. and Cooke, G. (2014) A study of dye anchoring points in half-squarylium dyes for dye-sensitized solar cells. Journal of Materials Chemistry A, 2, pp. 4055-4066. (doi:10.1039/C3TA15278B)

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Abstract

This paper reports the synthesis of a series of new half-squaraine dyes (Hf-SQ) based around a common chromophoric unit consisting of linked indoline and squaric acid moieties. Carboxylate groups have been incorporated onto this core structure at four different points to study the influence of the anchoring group position on dye-sensitized solar cell (DSC) device performance. Dyes have been linked to TiO2 directly through the squaric acid moiety, through a modified squaric acid unit where a vinyl dicyano group has replaced one carbonyl, via an alkyl carboxylate attached to the indole N or through a carboxylate attached to the 4 position of a benzyl indole. Contact angle measurements have been studied to investigate the hydrophobic/hydrophilic properties of the dyes and the results have been compared to N719 and Z907. Full characterization data of all the dyes and synthetic intermediates are reported including single-crystal X-ray structural analysis for dye precursors; the indole (2a) and the half-squarylium esters (3a) and (6b), as well as the dyes (4c), (8) and (12). Dye colours range from yellow to red/brown in solution (λmax range from 430 to 476 nm) with ε ranging from 38000 to 133100 M−1 cm−1. The performance of the dyes in DSCs shows the highest efficiency yet reported for a Hf-SQ dye (η = 5.0%) for 1 cm2 devices with a spectral response ranging from 400 to 700 nm depending on the dye substituents. Co-sensitization of half-squarylium dye (7b) with squaraine dye (SQ2) resulted in a broader spectral response and an improved device efficiency (η = 6.1%). Density functional theory (DFT) calculations and cyclic voltammetry have been used to study the influence of linker position on dye HOMO–LUMO levels and the data has been correlated with I–V and EQE data.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Cooke, Professor Graeme
Authors: Connell, A., Holliman, P.J., Davies, M.L., Gwenin, C.D., Weiss, S., Pitak, M.B., Horton, P.N., Coles, S.J., and Cooke, G.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Journal of Materials Chemistry A
Publisher:Royal Society of Chemistry
ISSN:2050-7488
ISSN (Online):2050-7496
Copyright Holders:Copyright © 2014 Royal Society of Chemistry
First Published:First published in Journal of Materials Chemistry 2:4055-4066
Publisher Policy:Reproduced under a Creative Commons License

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