Abstract
A new bipyridyl Ru(ii) sensitizer incorporating triphenylamine and the 3,4-ethylenedioxythiophene (EDOT) ancillary ligand IMA5 was synthesized for dye-sensitized solar cells (DSSCs). The performance of these DSSCs has been enhanced via di-anchoring metal-free organic sensitizers, denoted IMA1–4, with structural motif A–π–D–π–A and incorporating phenyl-dibenzothiophene-phenyl (Ph-DBT-Ph) as the main building block but with different anchoring groups (A). These new organic sensitizers were well-characterized and used as efficient co-sensitizers. Their photophysical, electrochemical and photovoltaic properties were studied. Furthermore, molecular modeling studies using DFT calculations were used to investigate their suitability as effective sensitizers/co-sensitizers. The molecular orbital isodensity showed distinguishable delocalization of the intramolecular charge in the DBT moiety. The photovoltaic characterization showed that IMA3 had the best DSSC performance (η = 2.41%). In addition, IMA1–4 was co-sensitized in conjunction with the newly synthesized IMA5 complex to enhance light harvesting across expanded spectral regions and thus improve efficiency. The solar cells co-sensitized with IMA2, IMA3 and IMA4 exhibited improved efficiency (η) of 6.25, 6.19 and 5.83%, respectively, which outperformed the device employing IMA5 alone (η = 5.54%) owing to the improvement in the loading of IMA2, IMA3 and IMA4 in the presence of IMA5 on the surface of the TiO2 nanoparticles, and charge recombination was suppressed.
Highlights
A new series of organic sensitizers IMA1–4 with A– p–D–p–A motif were synthesized and discussed along with the Ru(II) complex IMA5 to be used as effective sensitizers/cosensitizers for Dye-sensitized solar cells (DSSCs) and their performance, photophysics, electrochemistry and molecular modeling were compared
The DSSCs fabricated with sensitizers IMA1–4 showed photocurrent efficiency (PCE) performance that decreased in the order of IMA3 > IMA2 > IMA4 > IMA1, which depicts the anchoring nature (2-methylquinoline-6carboxylic acid, cyanoacetic acid, rhodamine-3-acetic acid, and 1phenyl-pyrazol-5-one-3-carboxylic acid)
IMA3 showed the highest PCE, which can be ascribed to the enhanced light harvesting coupled with better electron injection into the TiO2 conduction band, and, high electron injection efficiency owing to the presence of the quinoline ring between the anchoring group and the DBT center moiety
Summary
Compared to a single sensitizer.[26,27,28] This is attributed to preventing the aggregation of the dye and minimizing charge recombination, increasing the efficient accumulation of both types of dyes on the TiO2 surface owing to the difference in the molecular sizes of the dyes, facilitating the harvesting of a maximum number of incident photons by the cell.[29]. Scheme 1 Synthesis of bi-anchoring metal-free organic photosensitizers. The target molecules and all compounds were wellcharacterized using various spectral techniques, such as FT-IR, 1H-NMR and high-resolution mass spectroscopy analysis. Their optical bandgap (E0–0) and electronic energetics (GSOP and ESOP) were measured experimentally using cyclic voltammetry and the orbital charge distributions over the dye molecules were determined utilizing density functional theory (DFT)
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