Alloys and Compounds for Thermoelectric and Solar Cell Applications VIII: Session II
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, Ensicaen University of Caen; Philippe Jund, Montpellier University; Yoshisato Kimura, Tokyo Institute of Technology; Lan Li, Boise State University; Takao Mori, National Institute For Materials Science; Hsin-jay Wu, National Chiao-tung University; Tiejun Zhu, Zhejiang University
Tuesday 2:00 PM
February 25, 2020
Room: Miramar
Location: Marriott Marquis Hotel
Session Chair: Albert Wu, National Central University; Yoshisato Kimura, Tokyo Institute of Technology
2:00 PM Invited
Gradient Composition Layered Microstructure Development in Thermoelectric Mg2(Si,Sn) Alloys Based on Phase Equilibrium: Yoshisato Kimura1; Narumi Sakamoto1; Zhifang Zhou1; Yaw Wang Chai1; Yu Ikuta2; Yonghoon Lee2; 1Tokyo Institute of Technology; 2KELK Ltd.
Thermoelectric properties are sensitively affected by microstructure which changes during high temperature fabrication processes and practical long term operation. We focused on microstructure development in the Mg2Si–Mg2Sn pseudo-binary system. It is governed by phase equilibrium while being affected by kinetic factors such as diffusion rate, and so forth. The objectives of the present work are to characterize gradient composition layered microstructure, and to evaluate its effect on thermoelectric properties. We determined the Mg–Si–Sn ternary phase diagram focusing on the solidification route regarding the Mg2Si–Mg2Sn pseudo-binary system. It has been found that Mg2(Si,Sn) alloys have gradient composition layered microstructure which is basically formed according to the peritectic reaction, Mg2Sn is synthesized from liquid phase and Mg2Si, under the influence of the rate controlling due to diffusion and nucleation. The lattice thermal conductivity can effectively be reduced by phase interfaces of gradient composition layered microstructure.
2:20 PM Cancelled
Thermoelectric Properties of Amorphous ZnOxNy Thin Films at Room Temperature: Yasushi Hirose1; Masato Tsuchii1; Kei Shigematsu2; Yohei Kakefuda3; Takao Mori3; Tetsuya Hasegawa1; 1University of Tokyo; 2Tokyo Tech.; 3NIMS
Amorphous oxide semiconductors are potential thermoelectric materials for IoT energy harvesting applications, having low processing temperatures suitable for plastic flexible substrates. In this study, we investigated thermoelectric properties of amorphous ZnOxNy (a-ZnON) thin films. The a-ZnON thin films fabricated by nitrogen-plasma assisted pulsed laser deposition exhibited good n-type thermoelectric properties of power factor up to 204 μW∙m−1∙K−2. This value was more than twice higher than those reported for known amorphous oxide semiconductors. The thermal conductivity of the a-ZnON thin films were in the range from 1.1±0.2 to 1.4±0.2 W∙m−1∙K−1, which was comparably low in comparison to amorphous oxide semiconductors. Due to the better properties, the thermoelectric figure of merit reached 0.042 at room temperature, which is significantly higher than those of known amorphous oxide semiconductors.
2:40 PM
Heat Stability of Mg2Si1-xSnx as Affected by Heat Treatment Temperature and Duration: Mahdi Mejri1; Yohann Thimont1; Benoit Malard2; Claude Estournes1; 1CIRIMAT, Université de Toulouse, CNRS; 2CIRIMAT, Université de Toulouse, CNRS, INP-ENSIACET
A thermoelectric generator is a static and autonomous system that converts thermal energy into electrical energy and vice-versa. Degenerated semiconductors, including Mg2Si1-xSnx belong to the family of the most promising thermoelectric materials for medium temperature applications. Fully dense Mg2Si1-xSnx based materials have been elaborated using spark plasma sintering process. After sintering, due to the short time process, they present heterogeneities of composition. In order to stabilize them, heat treatments were carried out at different temperatures and holding times. Annealing at 750°C for 3 hours, the material remains biphasic with the presence of a Si rich phase (x→0.1) distributed in a matrix Sn rich one (x→0.6). Porosities were evidence due to Sn diffusion leading to Kirkendall effect. A swelling of the material was observed due to the change in composition and porosities creation. The microstructure and properties of the different materials will be discussed.
3:00 PM
Transmission Electron Microscopy Study of Hole-selective Contacts Employed in Silicon Solar Cells: Haider Ali1; Geoffrey Gregory1; Kristopher Davis1; 1University of Central Florida
Molybdenum oxide (MoOx) and tungsten oxide (WOx) are often employed as hole-selective contacts in crystalline silicon (c-Si) solar cells. Typically, ultra-thin (<10 nm) MoOx/ WOx is sandwiched between a-Si:H(i)/SiO2 (< 5 nm) passivation layer and either a transparent conducting oxide (e.g. indium tin oxide) or a metal contact (e.g. Al, Ni). The resulting contact structures not only provide efficient hole-selectivity but also results in very low surface recombination and minimal optical parasitic absorption. However, such contacts are sensitive to low temperature (≈ 200°C) anneal resulting in loss of cell efficiencies. To understand the origin of these losses, nanoscale characterization of these contact structures was performed with the help of transmission electron microscopy (TEM). It emerged that high-resolution TEM (HRTEM) imaging in combination with analytical TEM techniques (i.e. EDS, EELS) can be employed to detect the formation of interlayers as well as any elemental diffusion occurring within such contact structures.
3:20 PM Break
3:40 PM Invited
Thermoelectric Properties of p-type Mg Doped CuMO2 Delafossite Thin Films and Modules: Yohann Thimont1; Inthuga Sinnarasa1; Antoine Barnabé1; Philippe Tailhades1; Lionel Presmanes1; 1CIRIMAT, Universite de Toulouse, CNRS, Universite Toulouse 3 Paul Sabatier
The interest of thin films for thermoelectric (TE) applications growths for TE devices miniaturization. The TE applications based on the oxide materials show also some interests as: environment friendly, high stability and some combined properties (as optical).To satisfy these conditions, we have chosen to deposit p type 3% Mg doped CuMO2 (M was Cr or Fe) compounds on fused silica thanks to RF magnetron sputtering and thin films were annealed at various temperatures under vacuum. The physical properties as the Seebeck coefficients, the electrical and thermal conductivities were measured. The optimized annealed films showed a maximum of power factor of 85µW.m-1.K-2 for the 300nm Mg doped CuFeO2 thin film. A transparent unileg TE module has been elaborated with 100nm thick Mg:CuCrO2 tracks and allowed to produce a power of 11 nW when a Thot of 225°C was applied. This type of TE device could be advantageous for microelectronic applications.
4:00 PM Invited
Interfacial Reactions Between Bi2Te3 Substrate with Cu, In, Sn and Ni: Sinn-wen Chen1; How-wei Shih1; Wei Wang1; 1National Tsing Hua University
Bi2Te3 and its based materials are the most commonly used thermoelectric materials, and it is fundamentally important to understand the interfacial reactions between Bi2Te3 and possible contact materials. Interfacial reactions between Bi2Te3 and Cu, In, Sn and Ni are systematically examined. Significant interfacial reactions are observed in all the Cu/Bi2Te3, In/Bi2Te3, Sn/Bi2Te3 and Ni/Bi2Te3 couples. Te compounds, Cu2-xTe, InTe, SnTe and NiTe, are formed in these couples, respectively. In the Cu/Bi2Te3 and Ni/Bi2Te3 couples, liquation phenomenon was observed at 300℃. Since the reaction products are primarily Te-compounds, it can be concluded that Te in the Bi2Te3 substrate reacted with the contact materials, and the excess Bi became molten at 300℃. In the Cu/Bi2Te3 couples, a metastable (Cu)x(Bi2Te3)1-x was formed in the early stage of the reaction, and the metastable phase decomposed later and formed the Cu2-xTe and liquid phases. Similar phenomenon is being investigated in the Ni/Bi2Te3 couples.
4:20 PM Cancelled
3D Printing of High-performance and Flexible Thermoelectric Materials and Devices using 2D Colloidal Nanocrystals: Yanliang Zhang1; 1University of Notre Dame
The flexible thermoelectric generator (f-TEG) is a very promising technology for energy harvesting to enable self-powered wireless sensors and wearable devices, an area of exponential growth. Here, we present a scalable and cost-effective additive manufacturing process to fabricate f-TEGs using colloidal nanocrystals, and an innovative and highly efficient photonic sintering method to sinter large areas of printed films using pulsed light. The p-type and n-type printed films demonstrate peak ZTs of 1 and 0.43 near room temperature along with superior flexibility, which is among the highest reported ZT values in flexible materials. A flexible device fabricated using the printed films produces a high power density above 19 mW/cm2 with 80 ºC temperature difference between the hot side and cold side. The additive printing and photonic sintering can enable a highly scalable and low-cost roll-to-roll manufacturing process to transform high-efficiency colloidal nanocrystals into high-performance and flexible TEG devices for widespread applications.
4:40 PM
Assessment of Interface in Bi2Te3 and Sb2Te3 Thin Film Thermoelectric Modules: Zhen-Wei Sun1; Kai-Wen Cheng1; Albert T. Wu1; 1National Central University
Two-dimensional structural thin film thermoelectric module attracts interests due to its wide applications on different configuration of heat sources and have high flexibility of the material selection for substrates. Bismuth telluride and antimony telluride (Bi2Te3 and Sb2Te3) are promising thermoelectric (TE) materials due to their intrinsic small band gap (approximately 0.2 eV) and excellent zT values at operating temperatures. However, the transition efficiency drastically reduces after assembling as modules. Cu is usually selected as the material for electrode. However, it is not clear if the reaction between Cu and Te would affect the thermoelectric properties. In this study, a diffusion barrier is sputtered between the electrodes and the thermoelectric thin films. The module is aged to simulate the operating conditions for different duration of times. The interfacial morphology and the composition of the interaction layers are investigated. The stability of the interface and its effect on thermoelectric properties are assessed.
5:00 PM Invited
Synthesis, Processing and Characterizations of Functional Materials for Industrial Applications: David Berthebaud1; 1LINK (CNRS - Saint Gobain - NIMS)
LINK (Laboratory for Innovative Key Materials and Structures) is a Japanese-French joint laboratory between French CNRS, Saint-Gobain company, and National Institute for Materials Science, located at NIMS, Tsukuba, Japan. Our activity focus on the synthesis of new functional materials for energy and environment applications from functionalized glasses for building materials to high temperature thermoelectric materials for waste heat recovery in industrial furnaces. Here, I will briefly introduce our activities on functional nanocomposite materials (thin films), before presenting our work on thermoelectric materials with potential industrial applications to harvest waste heat and convert it into usable energy [1]. We focused our attention on environmentally-friendly thermoelectric compounds which not only exhibits high performance, but also possess the potential to be produced on large scale such as higher manganese silicide compounds. References[1] T. Mori, Novel Principles and Nanostructuring Methods for Enhanced Thermoelectrics. Small 2017, 13, 1702013
5:20 PM
High Reliability Package of Perovskite Solar Cell by SiNx Passivation Layer with Sn-Bi-In Low-melting Solder: Chun Kai Huang1; 1National Central University
Due to highly active of iodine ion, perovskite solar cell (MAPbI3) cannot withstand reflow temperature over 100℃ during package process. Therefore, low melting temperature of Sn-Bi-In solder was a promising material for the application on perovskite solar cell package. However, thin-film electrode of solar cell will be consumed during reflowing process, which is a great challenge to stability of perovskite solar cell. In this study, additional SiNx passivation layer and Ti/Ag metallization layers were deposited on electrode and enhanced 2.75 times lifetime of perovskite solar cell under atmosphere. We suggested that SiNx layer effectively avoided the solder diffusion to the Ag electrode and preventing the MAPbI3 from the environment. In addition, the mechanism of Sn-Bi-In solder bonding on SiNx layer will be further discussed. With proper packing structure, as-packing solar cell remains 94.1 % efficiency and 85.4 % efficiency after 24 hour sinking-water reliability test.