2017 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 |
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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, demonstrating high Seebeck coefficient, high power factor and high ZT value. In FY2017, specifically, the research focuses on the development of a robust platform to measure thermoelectric parameters of PbS QD assemblies. We developed on-chip measurement system by which the Seebeck coefficient and electrical conductivity were measured while varying the carrier density. We can increase the fidelity of the measurements to demonstrate the gate-dependent Seebeck coefficient, which reflects the band-filling of the discrete energy level of the QDs, thought to be the origin of the enhanced Seebeck coefficient (in mV/K order). Electrical transport measurement justifies the band-filling. We could elaborate the electronic state degeneracy on each discrete energy level, to start formulating a quantitative approximation on how much electrons should be doped into QDs to achieve enhanced Seebeck coefficient by other means (i.e. chemical doping). We acquired the first measurement of the thermal conductivity of the QD, to estimate the high ZT value. Also, the capability to synthesis PbS QD in-house is acquired, beneficial for the further continuation of the project. Also, we are developing a cryostat connected onto a glovebox to measure the temperature-dependent thermoelectric properties of the system and also to do doping by the frozen ionic liquid to fix the amount of carrier density. One paper is in submission and another three are in preparation.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
So far the research project is running as planned. Indeed, there are challenges in enhancing the fidelity of the measurements due to the nature of the thermal transport of the colloidal QDs. This challenge forced us only to concentrate on one system only, which is PbS QDs. On the other hand, we postpone the plan to measure also another QD system (i.e. PbTe), since we only just been able to control the electrical transport and the material is less stable than PbS. Furthermore, the glovebox-connected cryostat still needs fine tuning to function as intended. On the other hand, despite this deficiency, we can partially achieve some of the goals for the subsequent FYs related to improving the crystallinity of the QDs. Recently, we can control the superlattice formations of the QDs to form not only hexagonal or random lattices but also square lattices and honeycomb superlattices, by optimising the methods to assemble and to deposit the QDs. Furthermore, we have also explored some routes to dope the QD chemically. Through ligand variations and dopant-in-QD-matrix, we can hole-dope the QDs to become p-type transporting materials. On the other hand, attempts to stoichiometrically change the general composition of the QDs able to tune the carrier type. Both assembly improvement and the chemical doping are things to be further explored in the subsequent fiscal year.
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| Strategy for Future Research Activity |
In the next fiscal year, focus on the thermoelectric measurement will be slightly shifted not only on the field-induced doping by the ionic liquid to modulate the carrier density, but we will start to measure the influence of the chemical doping. For these chemically-doped systems, the ionic liquid gating will be used to quantitatively measure the numbers of dopant that have been introduced and how much dopants are still needed to be added to achieve the “peak” of Seebeck coefficient and conductivity. Furthermore, we will start to systematically measure the influence of the assembly orders towards the electrical transport and the generated Seebeck coefficient. One of the main particular interest is how the square superlattice and honeycomb superlattice behave. Furthermore, the size of these superlattices is still needed to be enlarged to achieve, hopefully, a single domain within a test device. Corresponding temperature dependent electronic transport will also be measured. In addition to PbS QD as the model system, we will also explore the measurements of some other metal chalcogenide QDs, including PbTe QD.
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