title: Double D-π-A dye linked by 2,2'-bipyridine dicarboxylic acid: influence of para- and meta-substituted carboxyl anchoring group.
abstract: Starting from 2,2'-bipyridine dicarboxylic acid, two new (D-π-A)2 sensitizers, including m-DA with the carboxyl anchoring group substituted meta to the donor-bridge moiety and p-DA with a para-substituted anchoring group, were synthesized in order to evaluate the impact of the position of the anchoring group on the optical, electrochemical, and photovoltaic properties of dye-sensitized solar cells. p-DA exhibits red-shifted absorption behavior compared to m-DA, owing to the more efficiently extended π-conjugation with para substitution. Both m-DA and p-DA are adsorbed on the mesoporous TiO2 surface by using both of their carboxylic acid groups in a bianchoring mode, which is confirmed through attenuated total reflectance FTIR analysis. Red-shifted absorption of p-DA assists the achievement of a red-shifted incident photon-to-electron conversion efficiency and a higher short-circuit current density than m-DA. The photogenerated electron lifetime in TiO2 is also found to be higher for para substituted p-DA than the meta-substituted m-DA, which results in a higher open-circuit voltage. All of the results suggest that dicarboxyl-2,2'-bipyridine can be used as an acceptor for metal-free organic sensitizers. However, the anchoring segments should be adjusted to the favorable position of the corresponding donor-bridge moieties for better conjugation.
authors: Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland); School of Chemistry, Bharathidasan University, Tiruchirappalli 620024, Tamilnadu (India).
authors: Paramaguru
authors: P
authors: Ganesan
authors: Aravind Kumar
authors: AK
authors: Chandiran
authors: Peng
authors: P
authors: Gao
authors: Renganathan
authors: R
authors: Rajalingam
authors: Michael
authors: M
authors: Grätzel
authors: Mohammad Khaja
authors: MK
authors: Nazeeruddin
keywords: 2,2′-bipyridine; bianchoring; double acceptor; dyes/pigments; solar cells