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Jpcl jz300652z diau presentation.pptx

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Design and Characterization of Heteroleptic Ruthenium Complexes Containing Benzimidazole Ligands for Dye-Sensitized Solar Cells: The Effect of Fluorine Substituents on Photovoltaic Performance
J. Phys. Chem. Lett., 2012, 3 (13), pp 1830–1835
DOI: 10.1021/jz300652z
We designed heteroleptic ruthenium complexes (RD12–RD15) containing fluoro-substituted benzimidazole ligands for dye-sensitized solar cells (DSSCs). These dyes were synthesized according to a typical one-pot procedure with the corresponding ancillary ligands produced in two simple steps; they were prepared into DSSC devices according to the same conditions of fabrication. The eventual devices show a systematic trend of increasing VOC and decreasing JSC with fluorine atoms of increasing number substituted on the ligand. The charge-extraction results show that upward shifts of the TiO2 potential occurred when the fluoro-substituted dyes were sensitized on TiO2 with a systematic trend of shift N719 > RD15 (with 5 F) > RD12 (with 2 F) >RD5 (no F); the intensity-modulated photovoltage spectra indicate that those fluoro substituents retard charge recombination with the electron lifetimes (τR) in the order RD15 > RD12 > RD5 > N719, consistent with the variation of VOC for the systems.

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  • Hello, I am Eric Diau from NCTU, Taiwan. I would like to take this opportunity to introduce our recent study on design and characterization of a series of novel heteroleptic ruthenium complexes containing benzimidazoleligands for dye-sensitized solar cells, and to highlight the effect of fluorine substituents to retard charge recombination for improved photovoltaic performance. The designed heteroleptic ruthenium complex involves a specific bidentate pyridine-benzimidazoleligand containing four substitutable functional groups labeled as A, B, C and D for which a structural modification can be easily achieved. Compared to other ancillary bipyridine-type ligands, the proposed pyridine-benzimidazoleligands have more flexibility for a structural design through proper molecular engineering to promote further the device performance.
  • In conclusion, novel heteroleptic ruthenium complexes containing fluoro-substituted benzimidazoleligands were applied to dye-sensitized solar cells. The corresponding devices show the increasing order of VOC consistent with the number of fluorine atoms on the substituted ligands; the trend of JSC is opposite. The charge-extraction and IMVS results indicate that the increase of VOC upon fluoro-substitution is determined by two factors – an upward shift of potential and a retardation of charge recombination. As a compromise for both VOC and JSC, the device made of RD12 gives the best performance because the potential shift, electron injection, charge recombination and charge collection are in a balance superior to that of the other systems.The synthesis and device characterizations were carried out by Mr. Wei-Kai Huang, and the charge extraction and IMVS measurements were performed by Ms. Hui-Ping Wu. This project is supported by National Science Council of Taiwan and Ministry of Education of Taiwan. Thank you for your attention.
  • Transcript

    • 1. Design and Characterization of Heteroleptic Ruthenium ComplexesContaining Benzimidazole Ligands for Dye-Sensitized Solar Cells: The Effect of Fluorine Substituents on Photovoltaic Performance Wei-Kai Huang, Hui-Ping Wu, Pi-Lun Lin, Yuan-Pern Lee, and Eric Wei-Guang Diau* Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan J. Phys. Chem. Lett. 2012, 31830-1832 1
    • 2. Synthetic ApproachProprietary and Confidential 2American Chemical Society
    • 3. Absorption and Emission Spectra RD5 Absorption Emission-1 RD12Absorption Coefficient /10 M cm 1.5 RD13-1 Emission Intensity /a.u. RD144 RD15 N719 1.0 0.5 0.0 300 400 500 600 700 800 900 Wavelength /nm The absorption spectra of RD12-RD15 resemble the spectrum of the RD5 dye, indicating that the effect of the fluoro substituents on the light-harvesting property is insignificant. The emission spectra of RD12-RD15 display blue shifts with respect to that of RD5. The positions of the intersection between the two spectra of each species determine the band gap energy of the dye. Proprietary and Confidential 3 American Chemical Society
    • 4. Potential Level DiagramThe potential level diagram of RD5, RD12-RD15 and N719 shows that theLUMO levels of the RD dyes become increasingly stabilized with anincreasing number of fluorine atoms, consistent with the electron-withdrawingnature of the fluoro substituents.Proprietary and Confidential 4American Chemical Society
    • 5. Photovoltaic Properties Voltage /V 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Our photovoltaic results demonstrate the 20-2 (a) same fluoro-substitution effect as those ofCurrent Density /mA cm 18 16 RD12-RD15 mentioned above (Table S2, 14 12 SI) with a systematic variation on VOC N719 10 RD5,  = 9.1 % > RD15 > RD12 > RD5 and an opposite RD12,  = 9.6 % 8 RD15,  = 9.2 % trend on JSC RD12 ~ RD5 > RD15 ~ N719. 6 4 N719,  = 9.3 % As a result, the overall device performance 2 exhibits a trend RD12 > N719 > RD15 ~ RD5, with the best device (RD12) attaining 80 (b) 70 an efficiency 9.5 % of power conversion, 60 superior to that of N719 ( = 9.3 %) under the same experimental conditions. IPCE /% 50 40 RD5 (DL = 270) 30 RD12 (DL = 260) Dye loading JSC VOC FF η Dye 20 RD15 (DL = 250) /nmol cm-2 /mA cm-2 /mV /% 10 N719 (DL = 170) RD5 270 17.150.26 73220 0.720.02 9.070.10 RD12 260 17.15±0.16 756±5 0.73±0.01 9.49±0.14 400 500 600 700 800 RD15 250 16.50±0.46 764±3 0.72±0.03 9.08±0.22 Wavelength /nm N719 170 16.57±0.16 776±5 0.72±0.01 9.30±0.12 Proprietary and Confidential 5 American Chemical Society
    • 6. Charge extraction and IMVS 0.80 The charge-extraction (CE) results (a) (a) indicate that the TiO2 potentials of the 0.75 devices show a systematic upward shiftVOC /V 0.70 with the order N719 > RD15 > RD12 > N719 RD5, consistent with the variation of their 0.65 RD15 VOC. Increasing substitution with fluorine RD12 atoms in the phenyl group hence shifts RD5 0.60 the potential of the conduction band edge of TiO2 in a more negative direction. The Intensity-modulated photovoltage 0.1 (b) spectral (IMVS) results indicate aR /s systematic trend with the electron lifetimes (corresponding to the degree of charge recombination) showing the order RD15 > RD12 > RD5 > N719, which is 0.01 3 4 5 6 7 8 consistent with the variation of VOC 18 -3 showing the same order for the fluoro- Ne /10 cm substituted devices. Proprietary and Confidential 6 American Chemical Society
    • 7. Conclusion RD12-RD15 containing fluoro-substituted benzimidazole ligands were designed and synthesized for dye-sensitized solar cells (DSSC). we measured charge-extraction (CE) and intensity-modulated photovoltage spectra (IMVS) at each VOC level. The CE and IMVS results indicate that the increase of VOC upon fluoro-substitution is determined by two factors – an upward shift of potential and a retardation of charge recombination. Increasing substitution with fluorine atoms produces to a more negative potential shift, but excess substituted fluorine atoms also result in a decreased JSC because of the lower LUMO level and the smaller amount of dye loading.AcknowledgmentsWe thank Prof. Chien-Chon Chen forproviding the Zahner equipment for theCE and IMVS measurements. NationalScience Council of Taiwan and Ministry ofEducation of Taiwan, under the ATUprogram, provided support for this project.Proprietary and Confidential 7American Chemical Society