Synthesis and characterization of novel heterocyclic π-conjugated systems for dye-sensitized solar cells (DSSCs)

The quality of human life depends to a large degree on the availability of energy, which is threatened unless clean and renewable energy sources are developed in the future. Science is expected to make important contributions to identify environmental friendly solutions for the energy problem. One attractive strategy is the development of photovoltaic cells, a promising source of renewable energy able to convert sunlight to electricity and with high potential to contribute significantly for solving the energy problem. Earlier, dye sensitizers applied in solar cells were mainly ruthenium complexes, consisting of the central metal ion with organic ligands containing an anchoring group. However, the lack of abundance of Ruthenium in nature, in addition with the latent risk to the environment, complicated synthetic processes and difficult purification methods, makes Ru-based dye sensitizers not suited in terms of cost efficiency and environmental friendliness. On the other hand, π-conjugated heterocyclic dyes of the type D-π-A are advantageous due to the structural diversity of the molecules that allows accurate adjustment of the photophysical and electronic properties, low cost of production, and environmental friendliness. The present communication reports the synthesis and evaluation of the DSSCs performance of a wide range of novel π-conjugated heterocyclic dyes bearing bithiophene or thienothiophene π-bridges functionalized with (hetero)aryl donor groups and cyanoacrylic acid or rhodanine acetic acid as anchoring groups. This multidisciplinary study shows that the improvement of the DSSCs performance can be achieved through the rational design of the dye in which several modifications on the π-bridge and/or on the donor and anchoring groups were performed.
Fundação para a Ciência e Tecnologia (FCT) and FEDER-COMPETE for financial support through the Centro de Química PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. We are also grateful to the Instituto da Educação of Universidade do Minho for providing the laboratory infrastructure necessary for the development of this work.