2019 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 / TD-DFT calculations / Dye sensitizers / Squaraine dyes / Anchoring group / DSSC |
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| Outline of Annual Research Achievements |
Combined theoretical and experimental approaches have been used for designing a series of novel NIR dyes having varying anchoring groups. Amongst newly designed NIR sensitizers, some of the potential candidates were not only synthesized but also subjected to their photophysical characterizations. In the fiscal year 2019 one paper was published in the international journals and eight presentations were made in the international as well as domestic conferences.
Success of computational molecular design relies on the accuracy of calculated results with that of the experimental values. Photophysical results for some of the experimentally synthesized dyes indicated only 60-70 nm (0.06 eV) in λmax and (±0.06 eV) in Eg difference between theoretical prediction and experiment results. At the same time, experimental energy diagram for six of the newly designed and synthesized dyes exhibits excellent match with the theoretically predicted results.
In order to utilize these newly designed dyes as sensitizer of dye-sensitized solar cells (DSSCs), kinetics of dye adsorption and their binding on to the mesoporous TiO2 was also conducted followed by fabrication and characterization of DSSCs using some of the selected dyes. It was demonstrated that nature of anchoring group not only controlled the rate of dye adsorption and their binding with TiO2 but also the overall stability of the DSSCs using them as sensitizer. Experimental results clearly revealed that bearing -PO3H anchoring group exhibited >70 times stronger binding as compared to the dyes with –COOH anchoring group.
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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
Energetic cascade amongst the sensitizer, mesoporous TiO2 and redox electrolyte is one of the important criteria for the optimal functioning of the DSSCs. We have used a new method to construct the theoretical energy band diagram utilizing QC calculations. Here HOMO energy level was calculated using 6-311G/DFT/B3PW91 and PCM model using Ethanol solvent. Optimized structures were then used for TD/DFT calculations and wavelength corresponding to the FWHM of calculated absorption spectrum was considered to be Eg followed by calculation of energy of LUMO. Out of 19 newly designed NIR dyes, six of them have been 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.
Phosphoric acid anchoring group containing dye (SQ-143) exhibited not only faster rate of dye adsorption, enhanced amount of dye loading, much higher binding strength on TiO2 and very high stability of the DSSC fabricated using this dye as compared to its –COOH anchoring group dye counterpart (SQ-138) but the photoconversion efficiency (PCE) was highly hampered (5-10 times lower). This was explained considering the intramolecular charge transfer (ICT) after the photoexcitation based on QC calculation. QC calculation results revealed that extent of the electronic coupling and ICT for SQ-143 bearing Phosphonic acid anchoring group was very much small as compared to that –COOH anchoring group bearing NIR dye (SQ-138), which could be responsible for the reduced PCE.
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| Strategy for Future Research Activity |
Our experimental results on some of designed NIR dyes bearing different anchoring groups revealed that nature of anchoring group not only affects the energetics but also the extent of electron density at LUMO, ICT and controlling the PCE as well as the stability. A good match between experiment and theory for some of the potential sensitizers motivated for the refinement of molecular framework aiming towards design of novel sensitizers having improved PCE in and stability of the DSSCs.
Based on feed of QC calculations on dyes with different anchoring groups, 8 of the NIR sensitizers out of 19 theoretically calculated have been already synthesized and rest of the potential sensitizers will 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, Photovoltaic performance and solar cell stability will be conducted.
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 the optimum molecular framework of the novel sensitizers having improved, PCE and stability.
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| Causes of Carryover |
Some of the materials were not able to be procured as planned and remaining money will be used in the next year.
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