Chemically and electrochemically deposited thin films of tin sulfide for photovoltaic structures
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1165-M08-35
Chemically and electrochemically deposited thin films of tin sulfide for photovoltaic structures Nini R. Mathews, David Avellaneda, Hiran B. M. Anaya, José Campos, M. T. S. Nair, P. K. Nair Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Temixco, Morelos-62580, México.
Abstract Thin films of tin sulfide (SnS) were deposited on TCO-coated glass substrates by pulse electrodeposition. Cyclic voltammetry showed that SnS deposition occurs in the -0.8 V to –1 V range. The films deposited using the potential pulses of -0.95V (Von) and +0.1V (Voff) are of orthorhombic crystal structure with lattice parameters and grain size similar to those of the thin films of orthorhombic structure obtained by chemical deposition. The optical band gap of the films was 1.3 eV. In CdS/SnS heterojunctions an open circuit voltage110 mV, short circuit current density 0.72 mA/cm2 and fill factor of 0.32 are reported here.
1. Introduction SnS thin films have been deposited by electrochemical [1], chemical bath [2], and spray pyrolysis [3] methods. In bulk crystals as well as in most of the thin films, SnS is reported as having an orthorhombic structure, similar to that of the mineral herzenbergite. Recently, we have reported the formation of polymorphic SnS (ZB) thin films consisting of both orthorhombic and zinc blende structures [2]. With p-type conductivity and optical bandgaps (Eg) in the range of 1.1 to 1.7 eV [1-6] along with the non-toxic nature of SnS and reasonable abundance (Sn, 2.2 ppm), these films have prospects as absorber components in solar cells. In CdS/SnS heterojunctions formed conversion efficiencies of 1.3% and 0.43% have been reported for SnS deposited by spray pyrolysis [7] and electrochemical [8] methods, respectively. Avellaneda et al have prepared CdS/SnS photovoltaic structures with CdS and SnS obtained by chemical deposition. They reported effect of annealing the SnS films and of metal contacts on SnS on the cell characteristics [2, 9]. Photovoltaic structures consisting of chemically deposited orthorhombic and polymorphic SnS (ZB) have shown an open circuit voltage, VOC, of 370 mV and a short circuit current density, JSC of 1.23 mA/cm2 with a fill factor (FF ) of =0.44 [9]. In this work we have used pulse-electrodeposition method for obtaining thin films of SnS and investigated the structural, optical and electrical properties of the films with a view to compare these with those of the chemically deposited thin films reported from our group previously. We have also investigated the characteristics of photovoltaic structures incorporating these films.
2. Experimental 2.1 Deposition of thin films a) Electrodeposition of SnS thin films We used solutions containing Sn(II) salts and Na2S2O3, as generally used [3, 8] for the electrochemical deposition of SnS. A three-electrode electrochemical cell consisting of TCO (Pilkington TEC -15) coated glass as working (cathode), a saturated calomel electrode (SCE) as reference and a platinum mesh as counter electrode was used. The react
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