Single-Source Approach for The Growth of I-III-VI Thin Films
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Single-Source Approach for The Growth of I-III-VI Thin Films Mohammad Afzaal,a Theivanayagam C. Deivaraj,b Paul O’Brien,a Jin-Ho Park,a and Jagadese J. Vittalb a
The Manchester Materials Science Centre and Department of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, UK. b Dept of Chemistry, 3 Science Drive 3,National University of Singapore, Singapore. E-mail: [email protected]; [email protected]; [email protected] ABSTRACT The ternary chalcopyrite semiconductors I-III-VI are currently used for photovoltaic solar cell applications. In this study, AgIn5S8 thin films were prepared from a series of single-source bimetalorganic precursors, e.g. [(PPh3)2AgIn(SC{O}R)4] (R = alkyl) by aerosol assisted chemical vapour deposition (AA-CVD). The compounds can be used as single-source precursors for the deposition of ternary compounds (I-III-VI) by one-pot reaction using CVD process and they are found to be air stable, which is favourable in comparison with metal alkyl compounds, which are found to be pyrophoroic. The optimum growth temperature for the preparation of these films on glass and Si(100) substrates, was found to be above 350 oC in terms of crystallinity, although deposition occurred at low temperatures. The films have been investigated using XRD, SEM and EDS. SEM analysis shows that all films are microcrystalline but have different morphologies depending on the growth temperatures. XRD results show evidence of the crystalline nature of these films. The results of this comprehensive study are presented and discussed. INTRODUCTION Chemists have been interested in synthesizing effective molecular precursors for various metal chalcogenides[1-4] in the past two decades. However, the possibility of single-source precursors for silver indium sulfide materials has been unexplored. Both AgInS2 and AgIn5S8 are known to be semiconducting.[5-8] AgInS2 finds applications as linear and non-linear optical materials. The band gap of AgIn5S8 is 1.80 eV (300K) and has been identified as making it a suitable candidate for photovoltaic solar cell applications.[9] Various metal monothiocarboxylates have been used as single-source precursors for metal sulfides.[10-12] Hence we attempted to synthesize bimetallic examples of such compounds which could be used as precursors to deposit silver indium sulfides. There are also some initial reports concerning the use of single-source organometallic precursors for the deposition of CuInS2 films. Hepp and co-workers reported spray CVD of CuInS2 films using a single-source precursor [13], (Ph3P)2Cu(µ-SEt)2In(SEt)2, which was previously reported by Kanatzidis and co-workers[14]. In their study, highly oriented CuInS2 was deposited on Si(111) substrates at 400 oC. Recently they also prepared a number of ternary single-source precursors, based on the [{ER3}2Cu(YR’)2In(YR’)2] (E = P, As, Sb; Y = S, Se and R = alkyl, aryl). [15] In this paper we report the growth of silver indium sulfide thin films from single-source precursors of the type [(Ph3P)2AgIn(SCOR)4] [
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