Research Article Adv. Mat. Lett. 2014, 5(11), 639-644 ADVANCED MATERIALS Letters Adv. Mat. Lett. 2014, 5(11), 639-644 Copyright © 2014 VBRI press www.amlett.com, www.vbripress.com/aml, DOI: 10.5185/amlett.2014.7589 Published online by the VBRI press in 2014 Optimization of thickness of Sb 2 Te 3 thin film as back contact for CdTe thin film solar cells Shailaja Jeetendra, Naveen C. Shivappa, Raghu Patel, Mahesh H. Matt* Department of Electronic Science, Bangalore University, Jnanabharathi, Bangalore 560056, Karnataka, India * Corresponding author. Tel: (+91) 9448233962, Fax: (+91) 80 22961552; E-mail: hm_mahesh@rediffmail.com Received: 05 July 2014, Revised: 29 July 2014 and Accepted: 03 August 2014 ABSTRACT Sb 2 Te 3 thin films of different thickness ranging from 100 to 500 nm were prepared on glass substrate by thermal evaporation method. The effects of thickness on structural, optical and electrical properties of thin films were studied. XRD revealed that grain size increases from 1.1nm to 98.7 nm with increase in film thickness. The internal strain and dislocation density decreased with increase in film thickness. The optical band gap decreases from 1.3 to 0.9 eV with increase in film thickness. AFM images indicated crystalline nature of Sb 2 Te 3 . Surface roughness increased up to 400nm after which it decreased. The resistivity decreases with increase in thickness at room temperature ranging from 2.9×10 -3 to 1.35×10 -4 Ωcm. The work function and barrier height decreases as the film thickness increases from 5.45 to 5.05eV and barrier height from 0.3 to -0.1eV. The results elucidate that Sb 2 Te 3 back contact of 400 nm thickness is ideal and efficient to be used in CdTe solar cell. Copyright © 2014 VBRI press. Keywords: Antimony telluride; Sb 2 Te 3 ; thermal evaporation; optical band gap; work function; electrical characteristics. Shailaja Jeetendra is a research scholar in Department of Electronic Science, Bangalore University, Bangalore. She received Master’s degree and Master of Philosophy in Electronic Science from Kuvempu University, Shimoga, Karnataka, India. Her active areas of research interest include thin film technology especially back contact for solar cells. Naveen C. S. is a full time research scholar in the Department of Electronic Science, Bangalore University, Bangalore. He received Master’s degree in Electronics from Kuvempu University, Shimoga, Karnataka, India. He had worked under BRNS major research project in 2013 and has authored research papers in peer reviewed national and international journals. His active areas of research interests include thin film devices especially thin film solar cells and oxide based antireflective thin films. Presently he is a CSIR sponsored senior research fellow. Mahesh Hampapatna Matt is presently working as an Associate Professor at the Department of Electronic Science, Bangalore University, Jnana Bharathi, Bangalore, Karnataka, India. He is a member of various Indian and International research organizations such as INS, NTSI. His research interests are thin film electronic devices (organic and inorganic), radiation effects on electronic devices, advanced communication systems. He has published more than 40 research articles in journals and has 100 plus conference proceedings to his credit. Introduction Sb 2 Te 3 , a chalcogenide, is a binary compound of the form A 2 VB 3 VI having a narrow band gap of E g ~0.2eV [1]. Investigations on Sb 2 Te 3 have been carried out for its semiconductor properties viz. high Seebeck coefficient, low thermal conductivity, low electrical resistivity, low band gap and long-term stability and the results of the same have been reported elsewhere [2]. Because of these characteristics it has found its applications in numerous areas like television cameras with photo-conducting targets, infrared spectroscopy, electronic and optoelectronic devices and thermoelectric devices [3]. One of the crucial applications of Sb 2 Te 3 is high efficiency stable electrical back contacts for CdS/CdTe based solar cells. There are many back contact materials available today, of which Cu or even materials doped with Cu have been used to form back contacts, such as ZnTe:Cu, Cu/Au, Cu/graphite, and Cu/Mo [4]. But, these suffer with few limitations. Cu- diffusion in CdTe is very rapid and extends deep into the absorber, thereby affecting the stability of the device considerably. Therefore, Cu-free alternative back contact materials like Sb 2 Te 3 can be embraced [5]. Fabrication of CdS/CdTe solar cell using Sb 2 Te 3 thin film as a back contact has been reported elsewhere. These solar cells have shown high efficiency of 14.6% and long-term device stability [6]. Considerable reports on various properties of Sb 2 Te 3 viz. optical and electrical properties, photoconductivity,