Enhanced thermoelectric properties of Al-doped ZnO thin films
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Enhanced thermoelectric properties of Al-doped ZnO thin films P. Mele1, S. Saini1, H. Abe2, H. Honda2, K. Matsumoto3, K. Miyazaki4, H. Hagino4, A. Ichinose5 1
Hiroshima University, Institute for Sustainable Sciences and Development, 739-8530 HigashiHiroshima, Japan, 2 Hiroshima University, Graduate School for Advanced Sciences of Matter, 739-8530 HigashiHiroshima, Japan, 3 Kyushu Institute of Technology, Department of Material Science, 804-8550 Kitakyushu, Japan, 4 Kyushu Institute of Technology, Department of Mechanical Engineering, 804-8550 Kitakyushu, Japan, 5 CRIEPI, Electric Power Engineering Research Laboratory, 240-0196 Yokosuka, Japan, ABSTRACT We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3 and Al2O3 substrates by Pulsed Laser Deposition (PLD) technique at various deposition temperatures (Tdep = 300 °C – 600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K - 600 K). AZO/STO films present superior performance respect to AZO/Al2O3 films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, with electrical conductivity 310 S/cm, Seebeck coefficient -65 μV/K and power factor 0.13 × 10-3 Wm-1K-2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to × 10-3 Wm-1K-2 at 600 K, surpassing the best AZO film previously reported in literature. INTRODUCTION The need for energy production and conservation in the industrialized world has generated interest in effective alternative energy approaches, to overcome the dependence of mankind from traditional energy sources (carbon, oil, and fossil fuel) and reduce the CO2 emission. Thermoelectric materials are considered extremely interesting from sustainable point of view because they can convert thermal energy to electrical energy [1]. The efficiency of thermoelectric energy conversion is determined by the dimensionless figure of merit ZT = ( σ.S2).T/κ
(1)
Where S: Seebeck coefficient; σ: electrical conductivity; κ thermal conductivity; T: absolute temperature [2]. Because of their poor conversion efficiency (below 20% for Bi2Te3-based devices [3]) thermoelectric materials have been restricted for a long time to a scientific scope. Efforts were made worldwide to enhance the performance of thermoelectric materials (i.e. the value of ZT) by increasing values of S, σ and at the same time lower the value of κ as much as possible. In past few decades materials such as silicon-germanium alloys, metal chalcogenides, boron compounds and many more were developed for thermoelectric applications. The performances of these materials were remarkable. For example, the value of ZT for metallic
thermoelectric Bi2Te3/Sb2Te3 multi layered films was reported up to 2.5 at T = 300 K [4]. However, their practical applications were limited because of low temperature decomposition, oxidation, vaporization or phase transition. These limitations have stimulated a lot of research on oxides as therm
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