AgSbSe 2 thin films for photovoltaic structures produced through reaction of chemically deposited selenium thin films wi
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AgSbSe2 thin films for photovoltaic structures produced through reaction of chemically deposited selenium thin films with Ag and Sb2S3 K. Bindu, M. T. S. Nair, and P. K. Nair Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Temixco, Morelos -62580, México [email protected]; [email protected] ABSTRACT Selenium thin films (350 nm) deposited from a 0.01 M solution of Na2SeSO3 of pH 4.5 maintained at 10 oC for 13 h, have been used as a source of selenium vapour for reaction with vacuum deposited Ag thin film on chemically deposited Sb2S3+Ag layers. When a stack of Sb2S3+Ag is heated in contact with Se film, AgSbSe2 is formed through solid state reaction of Sb2S3 and Ag2Se. The latter is formed at 80oC through the reaction of Ag-film in Se-vapour. This thin film is photoconductive and p-type. The optical band gap is nearly 1 eV and dark conductivity, 10-3 Ω-1cm-1. This thin film has been incorporated to form a photovoltaic structure, SnO2:F-(n)CdS:In-(i)Sb2S3(p)AgSbSe2-silver print. Voc> 400 mV and Jsc>12 mA/cm2 have been observed in this under an illumination intensity of 1 kWm-2.
INTRODUCTION I-III-VI2 compound thin films of chalcopyrite structure (I-Cu,Ag; III-In,Ga,Al; VI-Se,S) have been investigated during the past two decades motivated by the early success of CuInSe2 in the role of p-type absorber films in high efficiency solar cells [1]. The optical and electrical properties of some of I-V-VI2 compounds (I-Cu, Ag, V-As, Sb, Bi, VI-S, Se) are also promising [2]. The application of CuSbS2 thin films (Eg, 1.5 eV) as p-type absorber layer in a photovoltaic structure has been demonstrated [3]. For AgSbSe2 (NaCl structure), optical band gap of ~1 eV and p-type conductivity have been reported previously in thin films produced by thermal evaporation of powdered bulk material prepared by direct fusion of stoichiometric quantities of the elements [4]. In this paper, we report a novel method for producing AgSbSe2 thin films by heating a Sb2S3-Ag stack, with the Ag-side in contact with a chemically deposited Se thin film [5, 6], serving as a planar source for Se-vapour. Thin films of Sb2S3 have been prepared by chemical deposition [7] and the Ag thin films were deposited on it by vacuum evaporation. A two-stage process, consisting of the formation of Ag2Se films at about 80oC and its reaction with Sb2S3 film at 200-300oC lead to the formation of AgSbSe2 films. X-ray diffraction studies illustrate the evolution of the crystalline structure. Optical and electrical properties of the films are presented. The application of the films as a photovoltaic absorber layers is illustrated in the configuration, (n)CdS:Cl(i)Sb2S3-(p)AgSbSe2. EXPERIMENTAL DETAILS Deposition of Sb2S3 thin films, optical and electrical characteristics: Thin films of Sb2S3 were deposited on glass substrates (Corning, 75 mm x 25 mm x 1 mm) by chemical bath deposition, as reported earlier [7]. For this, 0.65 g of SbCl3 was dissolved in 5 ml of acetone in a 100 ml beaker. To this was added 25 ml (1 M) of Na2S2O3 (kept
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