2018 Fiscal Year Research-status Report
Elucidation of Stability of NIR Dyes Capable Efficient Photo-conversion by Logical Molecular Design
| Project/Area Number |
18K05300
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| Research Institution | Kyushu Institute of Technology |
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Principal Investigator |
PANDEY SHYAM S. 九州工業大学, 大学院生命体工学研究科, 准教授 (60457455)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Keywords | Structure optimization, / Dye sensitizers / TD-DFT calculations / Squaraine dyes / Anchoring group / DSSC |
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| Outline of Annual Research Achievements |
Combined theoretical and experimental approaches were used for design and development novel sensitizer of dye-sensitized solar cells (DSSCs) having same molecular framework but with varying anchoring groups. Amongst newly designed NIR sensitizers, some of them were also subjected to synthesis followed by their photophysical characterizations in order validate the accuracy of the calculated results. In the fiscal year 2018 one paper was published as conference proceeding, one submitted to international journals and seven presentations were made in the international and domestic conferences.
For practical application of DSSCs, kinetics of dye adsorption and strength of binding on the wide band gap semiconductor (TiO2 in present case) is highly desired. It has been found that nature of anchoring group controls the rate of dye adsorption which was found to be –OH<< -SO3H<PO3H<-COOH. Initial results on binding strength of newly designed dyes on mesoporous TiO2 has indicated that NIR dyes bearing -PO3H anchoring group exhibited much stronger binding as compared to the dyes with –COOH anchoring group.
Aiming towards validation of theoretical prediction for newly designed NIR sensitizers bearing varying anchoring groups, efforts were directed by taking unsymmetrical squaraine dyes in to consideration. It has been found that it is possible to predict the HOMO with in ± 0.1 eV, absorption maximum within 50-60 nm (0.05 eV) and energy band gap within ± 0.06 eV error with respect to the experimentally observed values utilizing suitable calculation parameters.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
A number of NIR light sensitive squaraine dyes with varying anchoring groups were designed using Gaussian program taking TD-DFT under 6-311G basis set along with their synthesis and photophysical characterizations for some of the completed dyes. Experimental results pertaining to the calculation of their energy band gap, HOMO/LUMO energies and electronic absorption spectra revealed that implementation functional like LSDA or B3PW91 functional the HOMO energy level within the accuracy of ± 0.1 eV and absorption maximum with only a difference of 50-60 nm (0.05 eV) as compared to the experimental data.
Considering the wide distribution in the width of the calculated absorption spectra, wavelength corresponding to full width at half maximum (FWHM) was assigned to energy band gap (Eg), which matches very well with the optical absorption edge of the experimental values obtained for the synthesized representative dyes. Using this calculated Eg and HOMO energy Value LUMO was calculated for all of the newly proposed dyes followed by construction of theoretical energy band diagram. Out of 15 newly designed NIR dyes, five of them were successfully synthesized and their experimental energy band diagram matches very well with that of the theoretically calculated counterparts having error of only ± 0.06 eV in the band gap.
Out of Efforts were also directed to investigate the implication of nature of anchoring groups on extent of intramolecular charge transfer (ICT) from HOMO to LUMO, rate of the dye adsorption behavior and binding strength on the mesoporous TiO2.
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| Strategy for Future Research Activity |
Our combined theoretical and experimental results on some of NIR dyes bearing different anchoring groups reveal that nature of anchoring group and their suitable positioning not only affects the energetics but also the extent of electron density at LUMO and ICT controlling the photovoltaic performance. A good match between experimental results and theoretical predictions for some of the potential sensitizers motivated for the refinement of molecular framework aiming towards design of novel sensitizers having improved photon harvesting in combination with good anchoring stability.
In parallel, rest of potential NIR sensitizers (10 out of 15) having different anchoring groups based on the feedback from our computational results, will also be synthesized and subjected to photophysical characterizations such as estimation of energies of HOMO & LUMO, energy band gap (Eg) and electronic absorption spectra. HOMO energy level will be experimentally determined using CV while Eg will be estimated taking the help of electronic absorption and fluorescence emission spectroscopies. Detailed investigation pertaining implications of nature of anchoring groups on the rate of dye adsorption, strength of binding on the mesoporous TiO2.
Finally, efforts will be directed to design and develop novel NIR dyes with extended pi-conjugation based on feed feedback from influence of anchoring group on ICT, energetics, adsorption behavior and binding strength in order to propose novel sensitizers with more effective NIR photon harvesting in combination with anchoring stability.
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