Characteristics of Chemically Deposited Thin Film Solar Cells using SnS and Sb2S3 Absorbers
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Characteristics of Chemically Deposited Thin Film Solar Cells using SnS and Sb2S3 Absorbers M. T. Santhamma Nair, David Avellaneda, Sarah Messina, and P. K. Nair Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Av. Xochicalco S/N, Temixco, Mexico ABSTRACT We use SnS and Sb2S3 thin films of about 500 nm in thickness deposited on glass substrates by chemical deposition to develop solar cell structures: glassSnO2:F/CdS/SnS/CuS/silver paint and SnO2:F/CdS/Sb2(S/Se)3/PbS/silver paint. Here, SnS and Sb2S3, and PbS are absorber materials suitable for large scale production, considering their abundance at 0.2 ppm (Sb) and 2 ppm (Sn) and 8ppm (pb) in the earth’s crust according to published data. SnS films deposited through distinct reaction routes have optical band gap of 1.1 eV or 1.7 eV. In SnO2:F/CdS/SnS(1.1eV)/SnS(1.7 eV)/CuS/silver paint, open circuit voltage (Voc) of ≈ 400 mV, and short circuit current (Jsc)of 7 mA/cm2 are obtained with a cell efficiency of 1%. Sb2S3 thin films have optical band gap 1.7 eV, but could be reduced through reaction in Se-vapor, upon which solid solutions of Sb2(S/Se)3 are formed. In SnO2:F/CdS/Sb2(S/Se)3/PbS/silver paint, Voc of ≈ 640 mV, Jsc of 7 mA/cm2 and conversion efficiency of 1.5% are obtained. INTRODUCTION Research on solar cells using Cu(In, Ga)Se2 and CdTe absorbers has led to laboratory scale devices with conversion efficiencies of >19.3 % and 16.5 %, respectively [1, 2]. However, cost-efficient processes in producing thin films on large areas, stability of back contacts in the case of CdTe cells, and scarcity of Indium and Te in the earth’s crust are important issues in large scale terrestrial application of photovoltaic modules based on these cells. Reports on thin film solar cells with Cu2ZnSnS4 of 4-5 % [3] conversion efficiency and with sulfosalts [4] with 1% conversion efficiency are encouraging results on alternate metal chalcogenides of more abundant elements as absorber components. Similar efforts with focus on low-cost processes and availability of materials for developing thin film solar cells from our group have produced promising results in chemically deposited photovoltaic structures incorporating chalcogenides of antimony [5-7] and tin [8] as absorbers. The present paper deals with the development of solar cell structures of SnS and Sb2S3 thin films of about 500 nm in thickness deposited on glass substrates by chemical deposition: glass-SnO2:F/CdS/SnS/CuS/silver paint and SnO2:F/CdS/Sb2(S/Se)3/PbS/silver paint. Here, SnS and Sb2(S/Se)3 are proposed as promising absorber materials for large scale production, considering their abundance at 0.2 ppm (Sb) and 2 ppm (Sn). We use chemically deposited PbS film also as an absorber layer. These are among the alternative materials to pursue new solar cell technologies.
EXPERIMENTAL DETAILS Deposition of thin films and solar cell structures: We deposited thin films of cadmium sulfide of approximately 100 nm or 200 nm thickness on to SnO2:F (transparent conducting oxide, TCO) coated
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