Jurnal Elektronika dan Telekomunikasi (JET), Vol. 20, No. 2, December 2020, pp. 82-88 Accredited by RISTEKDIKTI, Decree No: 32a/E/KPT/2017 doi: 10.14203/jet.v20.82-88 Thermopower Enhancement of Rutile-type SnO 2 Nanocrystalline Using Facile Co-Precipitation Method Nadya Larasati Kartika a, * , Budi Adiperdana b , Asep Ridwan Nugraha a , Ardita Septiani a , Dadang Mulyadi a , Pepen Sumpena a , Asep Rusmana a , Dedi a a Research Center for Electronics and Telecommunication Indonesian Institute of Sciences Kampus LIPI, Jl. Sangkuriang Building 20, 4 th Floor Bandung, Indonesia b Department of Physics, Faculty of Mathematics and Sciences Universitas Padjadjaran Sumedang, Indonesia Abstract Metal oxide semiconductor has attracted so much attention due to its high carrier mobility. Herein, thermoelectric study of nanocrystalline SnO2 through a simple co-precipitation method is conducted to enhance the Seebeck coefficient (S). X-ray diffraction, thermogravimetric analysis (TGA), resistivity (), Seebeck coefficient (S), and power factor (PF) measurements are conducted to analyze the thermoelectric properties of the material. The measurements show that there are two interesting results, which are the unusual resistivity behavior and the high value of the S. Resistivity behavior shows a non-reflective intermediate semiconductor-metals behavior where the turning point occurs at 250 o C. This behavior is strongly correlated to the surface oxide reaction due to annealing temperature. The maximum S likely occurs at 250 ºC, since the curve shows a slight thermopower peak at 250 ºC. The value of the S is quite high with around twenty times higher than other publications about SnO2 thermoelectric material, this happens due to the bandgap broadening. The energy gap of SnO2 calculated using density functional theory (DFT), which was performed by Quantum Espresso 6.6. The result shows that there is a broadening energy gap at different momentum or wave factor. Nanocrystalline semiconductors material is giving an impact to increase the width of bandgap due to quantum confinement and could enhance the thermopower especially in SnO2 nanocrystalline. Keywords: nanocrystalline, metal-oxide, thermoelectric, tin-dioxide, Seebeck, co-precipitation. I. INTRODUCTION Thermoelectric materials are promising candidates as harvesting energy devices for converting waste heat into electricity [1]. Thermoelectric could be applied as solid-state refrigerators or heat pumps. One advantage of thermoelectric is it does not use any moving parts and environmentally harmful fluids. Due to their high reliability and simplicity, thermoelectric materials are used extensively in fields such as space power generation and a variety of cooling applications [2]. Thermoelectric performance is determined by the dimensionless figure of merit (ZT) [2], [3], which is denoted by (1).  =  2   (1) where S is Seebeck coefficient representing a significant temperature difference which is required to generate electrical energy,  is electrical conductivity,  is thermal conductivity, and T is the absolute temperature. In order to increase thermoelectric material performance, elevating the optimization of the ZT value is required. To maximize ZT value, the S, large , and low  are needed simultaneously. However, there are conflicting parameters in optimizing ZT, since the S, , and  e are strongly coupled by carrier concentration (n), and difficult to control those variables independently following Wiedemann-Franz Law [4], [5]. Based on (1), to achieve a high ZT value, the enhancement of the S is needed. There are two conventional strategies to optimize the ZT values, which are: (1) enhancing the power factor (PF) by point defect engineering, and band engineering; (2) independently reducing the lattice thermal conductivity ( L) by structural nano-crystallization, interface engineering, and hierarchical architecting, or designing novel thermoelectric materials with intrinsically low  [6], [7]. A semiconductor material is a good candidate as a thermoelectric application since it can be doped to achieve a single n-type or p-type carrier for enhancing the S. A mixture of n-type and the p-type carrier will lead to lowering the S [8]. In other words, both low n and high n of semiconductor behavior can obtain large S. Several material types attracted so much attention in the thermoelectric application, such as chalcogenide metals [9], SiGe alloy [10], [11], silicon based thermoelectric materials [12], and skutterudites [13]. There are several thermoelectric materials commercially provided from low to high temperature, which are Bi 2 Te 3 (300–500 K) [14], PbTe (500–600 K) [15], and SiGe (600–800 K) [11]. The progress of thermoelectric material is still limited for practical application since * Corresponding Author. Email: nadya.larasati.kartika@lipi.go.id Received: October 14, 2020 ; Revised: November 25, 2020 Accepted: December 10, 2020 ; Published: December 31, 2020  2020 PPET - LIPI 25-32