2019 Fiscal Year Annual Research Report
量子ドットー有機分子複合系におけるアップコンバージョン機構に基づく太陽電池
| Project/Area Number |
19J14834
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| Research Institution | Kyoto University |
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Principal Investigator |
張 傑 京都大学, 理学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2019-04-25 – 2021-03-31
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| Keywords | Photon upconversion / Triplet energy transfer / Triplet annihilation / Quantum dots / Perylene |
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| Outline of Annual Research Achievements |
In this project, a triplet-triplet annihilation photon upconversion (TTA-UC) system based on the composites of organic molecules and inorganic quantum dots (QDs) was successfully established. QDs coordinated with the controlled number of surface-attached perylene-3-carboxylic acid (Pe) ligands were developed as a composite system for sensitizing TTA-UC. The mechanism and efficiency of triplet energy transfer at the QD-Pe interface were systematically investigated by transient absorption measurements. The UC efficiency of the composite system was measured by the UC measurements. Transient absorption measurements reveal that energy transfer efficiency increases with increasing n. The trend was heavily reflected in UC efficiency. Based on the finding, we propose that the intrinsic energy transfer efficiency from the QD to a surface-bound acceptor ligand provides a rational performance index for acceptor/QD composites. The result provides us with a useful guideline to achieve ideal UC efficiency. This work was presented on The 100th CSJ Annual Meeting, entitled “Number of Surface-Attached Acceptor Molecules on a Quantum Dot Impacts Energy Transfer and Photon Upconversion Efficiencies”.
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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
The progress of this research has gone well with our expectation. The mechanism of energy transfer was revealed by transient absorption measurements. As for charge transfer or Forster energy transfer in QD/organic molecule systems, the number of acceptor molecules attached on surface (n) plays an important role. In contrast, the effect of n on Dexter energy transfer is still unclear and remains controversial. In this project, we systematically investigate the effect of n on not only energy transfer at the QD/acceptor interface but also photon upconversion efficiency of the acceptor/QD composite annihilator system. Meanwhile, we also established a photon upconversion system that can upconvert near infrared (NIR) into visible light. A composite system was established by functinalizing PbS QDs with 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (TPP) molecules. NIR light (700 nm) was successfully upconverted into visible light (480 nm). Now the UC efficiency is still low (~1%) than the potential value as expected. I am planning to improve the UC efficiency to 10% by adjusting the parameter of the composite system.
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| Strategy for Future Research Activity |
Next year, I will construct photon upconversion assisted solar cells with photoelectric conversion efficiency over 15% by improving light-harvesting of NIR light. The photon upconversion assisted solar cell can be fabricated by assembling the efficient photon upconversion system into dye-sensitized solar cell. Low energy photons below the HOMO-LUMO gap of dye molecules (NIR light) can be absorbed by PbS QDs to suffer from photon upconversion to produce high energy excitons. Free electrons produced by photon upconversion are injected into the conduction band of the TiO2 nanocrystal. The photocurrent density-voltage (J-V) curves of solar cells is obtained by a Keithly model 2400 source measure unit and a solar simulator equipped as a light source. The incident-photon-to-current conversion efficiency (IPCE) spectra is measured as a function of wavelength using a specially designed IPCE system. The photoelectric conversion efficiency of the solar cell is expected to be improved from 10% to 15%.
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