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1012-Y12-29

SnS Thin Films in Chemically Deposited Solar Cell Structures David Avellaneda, M. T. S. Nair, and P. K. Nair Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Av. Xochicalco S/N, Temixco, Morelos, 62580, Mexico ABSTRACT We report photovoltaic cell structures on SnO2:F (TCO) coated glass substrates. Thin films of CdS, SnS, and CuS or PbS were deposited sequentially from chemical baths to produce the solar cell structures: SnO2:F-CdS- SnS (A)-CuS-Ag; SnO2:F-CdS- SnS (A)PbS-Ag; and SnO2:F-CdS- SnS (B)-PbS-Ag. Heating SnS-CuS films results in the formation of Cu2SnS3, and sequential depositions of SnS and PbS to obtain solar cells produce stratified layers as required for solar cells. The photovoltaic characteristics, Voc 340 mV and Jsc 6 mA/cm2 in these structures suggest that absorber thin films based on tin sulfide are worth investigating as a relatively abundant and non-toxic material for solar cells. INTRODUCTION Tin(II) sulfide crystallizes in an orthorhombic structure (a = 0.399 nm, b = 0.434 nm, c = 1.12 nm) [1, 2]. The direct band gap, Eg, reported for this material is 1.6 or 1.3 eV for polarized light with electric vector parallel to a-axis and 1.3 or 1.59 eV for the electric vector parallel to b-axis [3]. The indirect band gaps are: for a, 1.076 eV and for b, 1.049 eV [1]. The material is of p-type conductivity [4, 5] that can be controlled by doping. Reports on thin film heterojunction structures of nCdS-pSnS prepared with spray pyrolytically coated SnS [6] showing an open circuit voltage (Voc) of 260 mV and a short circuit current density (Jsc) of 9.6 mA cm-2 and that prepared with vacuum evaporated SnS [7] showing a (Voc) of 120 mV and a short circuit current density (Jsc) of 7 mA cm-2, both under an illumination of 100 mW cm-2, demonstrate the possible use of SnS, a relatively abundant and non-toxic material, as an absorber in solar cells. Recently, we reported photovoltaic structures prepared by the sequential chemical deposition of CdS and SnS on to commercial TEC-8 or15 (Pilkington, Toledo) conductive tin oxide film SnO2:F [8,9]. The current ñ voltage characteristics in the best of such cells show Voc of up to 380 mV. In this work, we present solar cell structures involving SnS-CuS and SnS-PbS absorber films along with the material characteristics of these layers. EXPERIMENTAL DETAILS Deposition of thin films to form solar cell structures We prepared the cell structures on SnO2:F (TCO) coated glass substrates (TEC-8 from Pilkington, Toledo). Thin films of CdS, SnS, and CuS or PbS were deposited sequentially from chemical baths to produce the solar cell structures: SnO2:F-CdS- SnS (A)-CuS-Ag; SnO2:F-CdS- SnS (A)-PbS-Ag; SnO2:F-CdS- SnS (B)-PbS-Ag. The

deposition baths (100 ml volume) and the conditions of depositions for the films are given below, with data on the relevant properties of the films. CdS - 25ml of 0.1 M cadmium nitrate, 15 ml of 1 M sodium citrate, 2 ml of 30% ammonia (aq), 5 ml of 1M thiourea, and water to make the volume up; 80 ∫C, 3h (100 nm); p