4:00pm - 4:30pmInvited
The Role of Molecular to the Thermoelectric Properties of Hybrid Perovskites
Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), Singapore
The organic-inorganic hybrid perovskite has been a popular material of research for its potential in efficient and economical photovoltaic technology. Recent experimental reports shown that these materials also hold a very low thermal conductivity of 0.3 W/mK to 0.5W/mK for poly-crystals and millimeter-size single crystals, respectively, telling that these materials could be utilized as thermoelectric materials. Theoretical researches on ABI3 with A=CH3NH3, NH2CHNH2 and B = Pb, Sn reported that the thermoelectric figure of merit, ZT, of these materials can reach value of 1 and 2 when it is electron doped. In this presentation, we report a systematic theoretical study on the role of molecular, CH3NH3 and NH2CHNH2, to the thermoelectric properties of hybrid perovskites via the structural evolution. Our report is based on calculated transport functions obtained from Boltzmann transport theory applied to the first-principles electronic structures.
4:30pm - 4:45pmOral
Composite Molecular and Nanomaterials
Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
Composite materials integrate two- or multi-components together with regular interface and lattice structures have demonstrated facinating performance in energy conversion and utilizations. Metal oxide mateirals are particularly attractive because their high thermal stability, excellent catalytic activity and structural compatibility with other mateirals. In the past few years, a series of functional molecular materials through green catalysis have been synthesized and investigated in magnetism, catalysis and luminescence. In this presentation, a series of composite metal oxide materials were desgined and fabricated using template-synthesis and in-situ procedures, their catalytic performance in CO oxidation and water oxidation reactions were evaluated. Some conductive films have also been fabricated using non-traditional approaches with enhanced electrical conductivity.
We appreciate the Institute of Materials Research and Engineering, A*STAR of Singapore for financial support.
 H.-L. Wu, R. Sato, A. Yamaguchi, M. Kimura, M. Haruta, H. Kurata, T. Teranishi, Science, 2016, 351, 1306-1310.
 W. G. Zeier, A. Zevalkink, Z. M. Gibbs, G. Hautier, M. G. Kanatzidis, G. J. Snyder, Angew. Chem. Int. Ed. 2016, 55, 2–18.
 W. Liu, K. Tang, M. Lin, L. T. J. Ong, S. Bai, D. J. Young, X. Li, Y.-Z. Yang, T. S. A. Hor, Nanoscale, 2016, 8, 9521–9526.
 S. Bai, D. Kai, K. L. Ke, M. Lin, L. Jiang, Y. Jiang, D. J. Young,X. J. Loh, X. Li, T. S. A. Hor, ChemPlusChem, 2015, 80, 1235–1240.
4:45pm - 5:00pmOral
Field-Effect Doping on Colloidal Quantum Dot Assemblies and its Implication on Thermoelectric Applications
1RIKEN Center for Emergent Matter Science, Japan; 2The University of Tokyo, Japan; 3ETH Zurich, Switzerland; 4EMPA Materials Science and Technology, Switzerland
Nanomaterials is one of the most promising building blocks to overcome the challenges in developing high performance thermoelectric materials.One of the most important feature of colloidal quantum dots (CQDs) is the formation of quasi-atomic discrete energy levels resulting from the quantum confinement effect. This feature lead to sharp density of states that beneficial for thermoelectric, if we are able to fill them. On the other hands, well-ordered tightly-bonded monolayers of solid assemblies of nanoscale QDs might be transparent for electrons to diffuse, but with large amount of boundaries for phonons to scatter. This would lead to the decoupling of electronic and thermal conductivity. While so far the most common approach to utilize colloidal QDs for thermoelectricity is limited as material sources for hot-pressed nanocomposite pellets and relies much on metal intercalation to enhance its electrical conductivity, exploitation of the preserved quantum confinement effect has yet to be explored.
Here we demontrate charge-density control on PbS and PbTe crosslinked CQD assemblies by field-effect doping utilizing electric-double-layer (EDL) gating. EDL gating enables the filling of carrier traps that would enhance the charge carrier transport in the assemblies. FETs with high electron mobility are demonstrated with mobility reaches values in the order of >10 cm2/V.s. The EDL gating also allows the probing of QD electronic band-gap by transport measurement, and accessing the preserved discrete energy levels from the observation of negative differential transconductance. The preservation of the discrete energy levels despite the large scale array of the assembly would enable us to expect the observation of high Seebeck coefficient for high performance thermoelectric devices when we access them. Furthermore, the optimized high electrical conductivity that are achieved can produce high power factor value. This provide new approach to develop efficient thermoelectric materials by controlling the appropriate carrier density required to dope QD superlattice.
5:00pm - 5:15pmOral
Organic–Inorganic Perovskite Single Crystal: A Potential Candidate in TE Application
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2School of Materials Science and Engineering, Nanyang Technological University, Singapore; 3Department of Mechanical Engineering and Centre of Nanofibers and Nanotechnology (NUSCNN), National University of Singapore, Singapore
The perovskite materials have emerged as a strong candidate in photovoltaic and solar cells. Based on unique properties of these hybrid lead perovskite such as high charge carrier mobility and high diffusion length, they have attracted intense attention for possible thermoelectric (TE) applications. Recently, we optimized a similar MAPbI3 crystal growth method to obtain a perfect centimeter-sized organic–inorganic hybrid perovskite (MAPbI3) single crystal. And obtained the Seebeck coefficient of 920±91 mV K-1 almost remained unchanged from room temperature to 330 K and it progressively increased with the increase in temperature and reached 1693±146 mV K-1 at 351 K. In contrast, there was no very clear trend for thermal conductivities with changes in temperature. The thermal conductivities were maintained between 0.30 and 0.42 W m K-1 in the temperature range of 298–425 K. It is envisioned that the MAPbI3 single crystal could be considered as a new class of thermoelectric materials if proper elemental doping can be incorporated to improve the electrical conductivity and in turn increase the overall figure-of-merit value.
5:15pm - 5:30pmOral
Organometallic Materials for Thermoelectric Applications
Institute for Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore
While renewable energy sources, such as wind or solar power, have received much attention as the solution to the global depletion of fossil fuels, energy recycling is an often overlooked method to address today’s energy and climate change problems. Since waste energy is largely produced in the form of heat, converting waste heat into electricity with a thermoelectric generator is a clean way of harnessing large amounts of untapped energy.
The fundamental principle of thermoelectricity is the Seebeck effect, where a temperature gradient across a conductor is converted into electrical potential. The efficiency of this conversion in a thermoelectric material is measured by the figure of merit, zT = α2σT/κ, where σ and κ represent electrical and thermal conductivity respectively, while T represents temperature and α, the Seebeck coefficient.
Traditional homogenous inorganic thermoelectric materials suffer from the coupling of all three thermoelectric parameters (i.e. increasing σ usually results in decreasing α and increasing κ); thus it is difficult to maximise ZT in bulk inorganic materials. Meanwhile, organic thermoelectric materials have intrinsically low κ, meaning σ and α can be tuned with little change in κ. However, optimization of ZT is often hindered by low carrier mobilities and α.
In this work, we leverage on our experience in organic synthesis and coordination chemistry to focus on hybrid organic-inorganic thermoelectrics, in particular coordination complexes. The network of metal ions interlinked with organic molecules would have low κ due to phonon scattering; and both the components can be easily tuned to obtain high σ and α. These materials should also be light-weight, flexible and non-toxic.
 Q. Zhang, Y. Sun, W. Xu and D. Zhu, Adv. Mater. 2014, 26, 6829.
 S.S. Goh, G. Chaubet, B. Gockel, M.C.A. Cordonnier, H. Baars, A.W. Phillips and E.A. Anderson, Angew. Chem. Int. Ed. 2015, 54, 12618
5:30pm - 5:45pmOral
Theoretical Study of the Thermoelectric Properties of Main-Chain Organometallic Polymers
Institute of High Performance Computing, Agency for Science, Technology and Research (A*STAR), Singapore
Thermoelectric (TE) materials have attracted much attention in recent years due to the capability of interconverting heat and electricity. Conducting polymers are lightweight, flexible and exhibit low thermal conductivity. Hence, conducting polymers are expected to be a class of good TE materials and exhibit advantages over conventional TE materials. The best organic TE materials so far have been reported to have a figure of merit (ZT) at 0.42. The main approach to increase ZT of organic TE materials is to optimize the Seebeck coefficient and electrical conductivity while maintain the low thermal conductivity . This can be archived by independently tuning the electrical properties. By ncorporating metal into the conjugated main-chain forming coordination polymer is expected to increase the conductivity while mention the low thermal conductivity of organic materials. Recently, we have investigated three different coordination polymer as proposed and synthesized by our collaborator. Through rational choose of different metals (Ni, Pd, Pt) and conjugated backbones based on N-Heterocyclic carbene (NHC) linker, we have successfully obtained some good TE materials with higher Seebeck coefficient than the reported results based on Poly(metal 1,1,2,2-ethenetetrathiolate). With Pd cation centers, the polymer have higher Seebeck coefficient. With Pt cation centers, the polymer have higher electrical conductivity. Meanwhile, by incorporating rigid pyridyl donor into NHC, the formed family of polymers have lower band gap. With further doping, the formed polymer might have better ZT.
 Kim, G.-H.; Shao, L.; Zhang, K.; Pipe, K. P. Engineered doping of organic semiconductors for enhanced thermoelectric efficiency. Nat. Mater. 2013, 12 (8), 719–723.
 Sun, Y.; Sheng, P.; Di, C.; Jiao, F.; Xu, W.; Qiu, D.; Zhu, D. Organic Thermoelectric Materials and Devices Based on p- and n-Type Poly(metal 1,1,2,2-ethenetetrathiolate)s. Adv. Mater. 2012, 24 (7), 932–937.