Solar cells with Sb 2 S 3 absorber films Sarah Messina ⁎, M.T.S. Nair, P.K. Nair Department of Solar Energy Materials, Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Temixco, Morelos 62580, Mexico abstract article info Available online 14 November 2008 Keywords: Antimony sulfide Thin films Solar cells Chemical deposition CdS/Sb 2 S 3 /PbS structures were prepared by sequential chemical deposition of CdS, Sb 2 S 3 and PbS thin films on TEC-8 (Pilkington) transparent electrically conductive SnO 2 (TCO) coatings. CdS thin films (100 nm) were deposited with hexagonal structure from Cd-citrate bath and of cubic structure from Cd-ammine/ triethanolamine bath. Sb 2 S 3 thin films were deposited at 40 °C from a solution mixture of potassium antimony tartrate, triethanolamine, ammonia and thioacetamide(TA) or at 1 to 10 °C from a mixture of antimony trichloride and thiosulfate (TS). These films were made photoconductive by heating at temperatures 250 to 300 °C. When heated in the presence of a chemically deposited Se thin film of 300 nm, a solid solution Sb 2 S 1.8 Se 1.2 resulted. PbS thin films of 100–200 nm thickness were deposited on the TCO/CdS/Sb 2 S 3 or TCO/CdS/Sb 2 S 1.8 Se 1.2 structure. Graphite paint was applied on the PbS film prior to applying a silver epoxy paint. The cell structures were of area 0.4 cm 2 . The best results reported here is for a cell: TCO/ CdS(hex-100 nm)/Sb 2 S 3 (TS-100 nm)/PbS(200 nm) with open circuit voltage (V oc ) 640 mV, short circuit current density 3.73 mA/cm 2 , fill factor 0.29, and conversion efficiency 0.7% under 1000 Wm - 2 sunlight. Four series-connected cells of area 1 cm 2 each gave V oc of 2 V and short circuit current of 1.15 mA. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Two distinct chemical formulations have been reported for the deposition of Sb 2 S 3 thin films [1–3]. The one using antimony chloride and thiosulfate (TS) solution mixtures typically gives thin films of 200 nm thickness in about 4 h at 2 to 10 °C [1,2]. These films have been integrated into distinct photovoltaic structures, with open circuit voltage (V oc ) of up to 640 mV and conversion efficiency approaching 1% [4,5]. The other formulation, using potassium antimony tartrate and thioacetamide (TA) solutions produce films of about 300 nm in thickness at deposition temperatures near 30 °C [3]. The use of such films in heterojunction solar cells has been demonstrated in 1994 [6,7]. In a recent paper [8], we reported the application of such films in all-chemically deposited solar cell structures with V oc of 640 mV and short circuit current density (J sc ) of 1 mA/cm 2 under an intensity of illumination, 1 kW/m 2 . Over all, in that study we observed that the cell performance did not differ much if the Sb 2 S 3 films were deposited using TS or TA as the sulfide source. Nevertheless, many aspects of this cell structure still remain to be explored, such as the role of the individual films constituting the cell structure, the benefit of using a solid solution, Sb 2 S 3-x Se x , optimum thickness of the PbS thin film, etc. In this article we report some characteristics of the thin films, and of the cell structures which result from them. 2. Experimental details Two types of substrates were used for the experiments: (i) 25 mm × 75 mm Corning microscope glass slides of 1 mm thickness or (ii) TEC-8 transparent electrically conductive SnO 2 (TCO) coating with sheet resistance 8 Ω on 3 mm float glass sheet (Pilkington, Toledo). They were cut into 25 mm× 75 mm pieces. The substrates were cleaned in a neutral soap solution, rinsed in water and dried. 2.1. Thin film deposition 2.1.1. CdS window layer [8,9] CdS thin film of 100 nm thickness and of predominantly hexagonal (hex) crystal structure was deposited from a solution mixture contain- ing: 25 ml of 0.1 M cadmium nitrate, 15 ml of 1 M sodium citrate, 2 ml of 30% (15 M) ammonia (aq.), 5 ml of 1 M thiourea, and water to take the volume to 100 ml. Baker Analyzed reagents were used. Substrates were kept in the bath vertically and maintained at 60 °C for 3 h. In the case of CdS films of cubic (cub) structure [10], the bath consisted of 5 ml 0.1 M cadmium nitrate, 5 ml triethanolamine (TEA), 5 ml 16 M ammonia (aq.) and 5 ml 0.1 M of thiourea and water to complete a volume of 100 ml. A 100 nm film was obtained in 1 h at 80 °C. We shall refer to CdS(hex) or CdS(cub) for the CdS thin films deposited as above from the two baths. 2.1.2. Sb 2 S 3 film In the TA method [3,8], the solution mixture contained: 25 ml of 0.1 M potassium antimonyl tartrate (K 2 Sb 2 C 8 H 4 O 12 ·3H 2 O), 10 ml of Thin Solid Films 517 (2009) 2503–2507 ⁎ Corresponding author. E-mail address: srmf@cie.unam.mx (S. Messina). 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.11.060 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf