Investigations on structural, optical and thermoelectric parameters of spray deposited bismuth selenide thin films with different substrate temperature Sharmistha Anwar * , Shahid Anwar, Barada Kanta Mishra, Saroj kumar Singh CSIR e Institute of Minerals & Materials Technology, Bhubaneswar, Odisha 751013, India highlights  Influence of substrate temperature on the deposition of Bi 2 Se 3 has been shown.  Bi 2 Se 3 SEM microstructure strongly depends upon the change in substrate temperature.  Seebeck measurements at 300  Ce500  C confirms n-type conductivity.  Improved Seebeck coefficient has been observed at high temperature deposited film. article info Article history: Received 25 March 2014 Received in revised form 27 June 2014 Accepted 22 July 2014 Available online xxx Keywords: Thin films Chemical synthesis Electron microscopy Thermoelectric effects abstract A series of Bi 2 Se 3 films was deposited at different substrate temperature in 150e500  C temperature range using spray pyrolysis technique, in order to study the effect of substrate temperature on structural and thermoelectric properties. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of hexagonal Bi 2 Se 3 . Scanning electron microscopy examination indicates that the Bi 2 Se 3 microstructure strongly depends upon the change in substrate temperature. The optical absorption study shows that the direct band gap of the film decreases with increase in substrate temperature. The thermoelectrical measurements have shown n-type conductivity in as deposited films and the magnitude of Seebeck coefficient for films has been found to be increasing with increasing deposition temperature. Improved thermoelectric properties at higher substrate temperature shows promising aspect and Bi 2 Se 3 films could be a good thermoelectric material at lower temperature range. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Thermoelectric energy conversion, which directly transforms heat into electricity, has drawn much attention in recent years and found applications in a variety of areas such as renewable and clean energy, thermoelectric power generation, small scale cooling sys- tems for electronic devices, micro refrigerator devices, and micro- thermo-chemistry on a chip for microelectronic components, etc [1,2]. Seebeck coefficient (S) represents the rate of voltage variation per unit temperature change (DV/DT) for the materials. This coef- ficient is very low for metalsdmeasuring up to few mV/K and much larger for a semiconductor which is of the order of 100 mV/K. The performance of thermoelectric devices is evaluated by materials dimensionless figure of merit (ZT) or the power factor. ZT is defined as S 2 sT/k and the power factor is S 2 s, where S is the Seebeck co- efficient, s is the electrical conductivity, k is the thermal conduc- tivity and T is the temperature [3]. Compounds of the column V-A (Sb, Bi, etc) and VI-A (S, Se, Te, etc) elements in the periodic table with chemical formula A 2 V-A B 3 VI-A have bismuth sulphide type structure, which is one of the impor- tant material for photosensitive, photoconductive and thermo- electric applications [4e13]. Bi 2 Se 3 , with a band gap of ~0.3 eV, belongs to a same class of family with a narrow band gap layered semiconductors with tetradymite structure [14e16]. It is attractive for good electrical conduction due to the existing six valley de- generacy and the narrow energy band gap. Furthermore, its layered crystal structure gives rise to a poor thermal conductivity, making these layered materials suitable for thermoelectric applications [2]. Over the years, a wide variety of synthesis techniques have been * Corresponding author. E-mail addresses: bagchi.sharmistha@gmail.com, sharmisthabagchi@immt. res.in (S. Anwar). Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys http://dx.doi.org/10.1016/j.matchemphys.2014.07.039 0254-0584/© 2014 Elsevier B.V. All rights reserved. Materials Chemistry and Physics xxx (2014) 1e6 Please cite this article in press as: S. Anwar, et al., Investigations on structural, optical and thermoelectric parameters of spray deposited bismuth selenide thin films with different substrate temperature, Materials Chemistry and Physics (2014), http://dx.doi.org/10.1016/ j.matchemphys.2014.07.039