2018 Fiscal Year Annual Research Report
High Performance Room-Temperature Thermoelectric Device using Colloidal Quantum Dot Superlattice
| Project/Area Number |
17H04802
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
Bisri Satria 国立研究開発法人理化学研究所, 創発物性科学研究センター, 研究員 (70748904)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | colloidal quantum dots / thermoelectric / self-assembly / hybrid materials |
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| Outline of Annual Research Achievements |
This project aims to develop high-performance thermoelectric generator based on colloidal quantum dot (QD) assemblies. In FY2018, specifically, the research focuses on the improvement of the QD assemblies quality to form a well-controlled 2D superlattices, and to formulate chemical doping strategies for the QD assemblies. We diversified our techniques in fabricating QD assemblies in addition to layer-by-layer spin coating method. The new methods include the deposition via dip coating and the establishment of liquid/air interface assembly. Through the comparisons of these three methods, we were able to identify the structures beneficial for different kinds of applications, including the thermoelectric direction. The liquid/air interface assembly enable the formation of large scale square and honeycomb-like superlattices via control of QD facet and ligand stripping. As results, we were able to obtain large-scale well-ordered superlattices with various forms reproducibly. Electrical properties were measured, where the filling of the discrete energy levels of the QDs were also demonstrated. We also developed several routes to perform chemical doping into the QD assemblies. Besides through development of new ligands, we performed remote doping methods, where some charge transfer molecules were used as dopant. Depending on the used molecules, the charge carrier type can be selected and the electrical conductivity significantly enhanced. However, we have not reached a capability to fill the QD discrete energy levels, similar to thing achieved by field-induced doping.
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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
So far, many aspects of the research project is running as planned. For many target that wanted to be achieved in FY2018 were realized. In particular those were related with the improvement of the assemblies and the exploration of doping methods. We have discovered the mechanism to form large scale square lattice assembly, with and without ligand exchange. Control of carrier types in QD assemblies were demonstrated by doping them using several different charge transfer molecules. Exclusive electron transport was demonstrated in core@shell QDs, beneficial for TE operation. However, there are several challenges. While electrical performance of these system are controlled, including the reproductions of band fillings, to have sample stable enough for Seebeck measurements under field-induced doping are still difficult. Therefore, the yield of measurement is still very low. On the other hand, while the measurements of the chemically-doped QD assemblies seem to be more straightforward, the current doping levels that have been achieved is still far from the filling of the QD discrete energy levels, where the enhanced Seebeck is expected. Also, in many of the chemically-doped system that we developed, some of the outcomes are counter-intuitive with we expected. This counter-intuitive results might stem from the fact we need to control the surface properties of the QDs, which seems much of the current knowledge is still inadequate. While it is challenging, this also show the potential to generate many new knowledge related with this material system.
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| Strategy for Future Research Activity |
In the next fiscal year, the focus of the research will refocus on the thermoelectric measurement of the much-improved QD assemblies. Related with the instability in the field-effect modulation of thermoelectric properties, as planned, we will employ some frozen ionic liquid gating method using the developed system. With this method, hopefully we can control the charge carrier density in much stable way in the electric-double-layer system. Selections of several ionic liquids, which have solidifying point close to room temperature and with large electrochemical window may be beneficial. Furthermore, effort to chemically-dope these QD assemblies will be intensify by optimizing the developed doping methods and trying several post-synthesis doping directly on the QD surface, including shelling. The use of our success long ligands to provide nanospace for remote chemical doping will be attempted. Also, in response to several feedback from publication reviewers which emphasize the importance to compare both 2D assemblies system and 3 assemblies system, we start performing preparation of QD inks where the ligand exchange is performed in solution, ideal for making thick film. Measurement of highly-doped thick QD film is also one target to be achieved in the next fiscal year.
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[Presentation] Morphology Control of Colloidal Quantum Dots Assembly and Its Implication towards Electronic Transport2018
Author(s)
Ricky Dwi Septianto, Satria Zulkarnaen Bisri, Liming Liu, Yasuhiro Ishida, Takuzo Aida, Maksym Kovalenko, Ferry Iskandar, Yoshihiro Iwasa
Organizer
3rd Materials Research Society of Indonesia (MRS-ID) Meetings, Denpasar, Bali, Indonesia
Int'l Joint Research
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