CuIn 1 À x Ga x Se 2 thin-film absorber layers for solar photovoltaics fabricated by two-stage pulsed current electrodeposition Sreekanth Mandati a,b , Bulusu V. Sarada a,n , Suhash R. Dey b , Shrikant V. Joshi a a International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Balapur, Hyderabad 500005, Andhra Pradesh, India b Department of Materials Science and Engineering, Indian Institute of Technology Hyderabad, Yeddumailaram 502205, Andhra Pradesh, India article info Article history: Received 20 August 2013 Accepted 15 December 2013 Available online 22 December 2013 Keywords: Electrodeposition Thin films Solar energy materials Pulsed current Two-stage CIGS abstract Single phase polycrystalline Copper Indium Gallium Diselenide (CIGS) thin-films for solar photovoltaic applications were fabricated by an economical two-stage method of Pulsed Current (PC) electrodeposi- tion. Cu, Ga and Se were first co-deposited onto a Mo foil followed by deposition of In. The as-deposited films were annealed in Argon atmosphere at 550 1C for 30 min and were further characterized to study their morphology, phase constitution, and optical absorption. The results revealed that the films have a compact morphology and are comprised of a crystalline chalcopyrite single phase CIGS. The bandgap of the CIGS films was found to be 1.27 eV from absorption studies. The photoelectrochemical studies revealed the p-type nature of CIGS films with improved photocurrent over that obtained for one-stage PC electrodeposited CIGS thin-films. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Cu(In, Ga)Se 2 (CIGS) is one of the most promising semiconductor absorber layer materials among thin-film based solar cells, due to its suitable bandgap, large optical absorption coefficient and high stability [1]. CIGS alloys have been extensively prepared using several techniques [2,3]. However, an economical and simple method like electrodeposition is preferred for scaling up to industrial level. In this context, the advantages of Pulsed Current (PC) electrodeposition have been detailed in our previously reported work [4]. Electrodeposition of Cu–In–Ga–Se has been previously reported for fabrication of chalcopyrite CIGS thin-films. However, the film composition has been found to deviate from the ideal stoichio- metry, resulting in the formation of undesired phases [5]. Easier control over the composition of individual elements has been reported by several researchers using multi-stage Direct Current (DC) electrodeposition of CIGS thin-films resulting in higher efficiencies [6–8], but relies on use of additives and an additional selenization step to improve the morphology and stoichiometry of the films. In the present work, PC electrodeposition with a two-stage approach consisting of a two electrode system is employed for the first time to fabricate stoichiometric chalcopyrite CIGS (CGS/In) thin- films on a Mo foil. This technique is novel in that it overcomes the stoichiometry related problems associated with the single-step method and also obviates the use of complexing agents or an additional selenization step as employed in other previously reported multi-stage methods. The resulting films are found to exhibit a compact morphology devoid of undesirable phases, resulting in superior photoelectrochemical performance compared to the single-stage electrodeposited CIGS films reported previously [9]. 2. Materials and methods Electrodeposition of Cu–Ga–Se was carried out using a bath containing CuCl 2 (3 mM), GaCl 3 (8.5 mM), H 2 SeO 3 (8.5 mM) and LiCl (250 mM) dissolved in Hydrion buffer (pH 3), followed by In deposition in the second stage using InCl 3 (3.2 mM) in Hydrion buffer. Pulse electrodeposition (Dynatronix Pulse Power Supply) was performed in a vertical cell with high purity graphite plate as an anode and Mo foil (25 μm thick) as a cathode. An elaborate procedure was adopted for cleaning the Mo foil prior to deposition [4]. Such a two electrode system is more suitable for larger area thin- films and is commonly practiced by the electroplating industries. A pulse period of 20 ms, duty cycle of 50% and deposition potential of À 1.5 V were used in both stages. The depositions of Cu–Ga–Se and In were carried out for 15 min and 8 min respectively, while maintain- ing the bath at room temperature without stirring, in the first and second stages for achieving stoichiometric CIGS. In comparison to a classical three electrode system, no significant difference in the features of the electrodeposit was observed with the use of a two electrode system [4,9,10]. The electrodeposited films were annealed at 550 1C for 30 min under Ar atmosphere. Annealing at a Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.12.063 n Corresponding author. Tel.: þ91 40 24452448; fax: þ91 40 24442699. E-mail address: sarada@arci.res.in (B.V. Sarada). Materials Letters 118 (2014) 158–160