All-Chemically Deposited Solar Cells with Antimony Sulfide-Selenide/Lead Sulfide Thin Film Absorbers
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1012-Y12-23
All-Chemically Deposited Solar Cells with Antimony Sulfide-Selenide/Lead Sulfide Thin Film Absorbers Sarah Messina, M.T.S. Nair, and P. K. Nair Centro de InvestigaciÛn en EnergÌa, Universidad Nacional AutÛnoma de MÈxico, Av. Xochicalco S/N, Temixco, Morelos, 62580, Mexico ABSTRACT Solar cell structures with Sb2SxSe3-x and PbS as absorber layers were fabricated on commercial transparent conductive oxide coated glass by chemical deposition. The solid solution with a graded band gap of 1-1.8 eV was prepared by heating at 250°C an Sb2S3 thin film in contact with a chemically deposited Se-thin film. A PbS thin film deposited on this layer basically fulfils the role of a p+ layer; its role as an absorber is yet to be studied. Open circuit voltage of 560 mV and short circuit current density ≈ 0.5 mA/cm2 under 1 kW/m2 tungsten halogen radiation are characteristics of these cells. These results may form the basis for developing an alternative thin film solar cell technology. INTRODUCTION In this work we report the fabrication of solar cell structures by chemical deposition, which offers easy scale-up [1]. We choose here an absorber material Sb2SxSe3-x, which can have an optical band gap (Eg) between that of Sb2S3 (≈ 1.8 eV) and Sb2Se3 (≈ 1.0 eV). Even though PbS thin films have been used as absorber in CdSPbS junctions previously [2], its integration into the cell structure here is to serve as a p+ layer. Chemically deposited CdS window layers of ≈ 100 nm may be predominantly hexagonal [3] or cubic [4] and both would be tested in the cell structures. The first step in the formation of the solid solution is the deposition of Sb2S3 thin film of ≈ 500 nm in thickness from a solution mixture of antimony chloride and thiosulfate [5, 6]. When this film is heated in contact with a chemically deposited Se- thin film [7], a solid solution Sb2SxSe3-x would result [8]. A PbS thin film of ≈ 200 nm can be added on this by chemical deposition [9] to complete the cell structure. The absorber materials presented here may be optimized to improve upon the cell characteristics. EXPERIMENTAL Transparent conductive oxide (TCO) coatings, SnO2:F TEC-8 or TEC-15 from Pilkington, Toledo, were used as the substrates for the photovoltaic structures. CdS films of predominantly hexagonal phase [3] were deposited on these substrates using 25 ml 0.1 M cadmium nitrate, 15 ml 1 M sodium citrate, 2 ml 15 M ammonia (aq.) and 5 ml 1 M thiourea and added water to complete a volume of 100 ml. At 60°C in 3 h or at 80°C in1 h, a film thickness of 100 nm is obtained. For depositing CdS films of predominantly cubic phase [4], 5 ml 0.1 M cadmium nitrate, 5 ml triethanolamine (TEA), 5 ml 15 M ammonia (aq.) and 5 ml 0.1 M of thiourea were mixed and water was added to complete a volume of 100 ml. A 100 nm film was obtained in 1 h at 80°C. For depositing Sb2S3 thin films [5, 6], 650 mg of antimony trichloride was dissolved in 2.5 ml of acetone and 25 ml 1 M of sodium thiosulfate and water were added to complete a volume of 100 ml. At 1°C a film thickness ≈ 5
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