Characterization of CuInS 2 thin films prepared by chemical bath deposition and their implementation in a solar cell S. Lugo a , I. López a , Y. Peña a, ⁎, M. Calixto b , T. Hernández a , S. Messina c , D. Avellaneda d a Universidad Autónoma de Nuevo León, UANL, Facultad de Ciencias Químicas, Laboratorio de Materiales I, Av. Universidad, Cd. Universitaria 66451, San Nicolás de los Garza, Nuevo León, México b Instituto de Energías Renovables, Universidad Nacional Autónoma de México, C.P. 62580, Temixco, Morelos, México c Universidad Autónoma de Nayarit, Ciudad de la Cultura “Amado Nervo”, S/N C.P. 63155, Tepic, Nayarit, México d Universidad Autónoma de Nuevo León, UANL, Facultad de Ingeniería Mecánica y Eléctrica, Av. Universidad, Ciudad Universitaria 66451, San Nicolás de Los Garza, Nuevo León, México abstract article info Article history: Received 28 January 2014 Received in revised form 27 August 2014 Accepted 29 August 2014 Available online 4 September 2014 Keywords: Copper indium sulfide Thin film absorber Chemical bath deposition Photovoltaics Solar energy CuInS 2 thin films were formed by the sequential deposition of In 2 S 3 –CuS layers on glass substrates, by chemical bath deposition technique, and heating these multilayer 1 h at 350 °C and 400 mPa. The morphology and thickness of the CuInS 2 thin films were analysed by scanning electron microscopy, showing particles with elongated shape and length about 40 nm, and thickness of 267 and 348 nm for samples from 15 and 24 h of deposition time in the chemical bath of In 2 S 3 , respectively. The energy band gap values of the films were around 1.4 eV, whereas the electrical conductivity showed values from 64.91 to 4.11 × 10 -3 Ω -1 cm -1 for the samples of 15 and 24 h of In 2 S 3 deposition bath, respectively. The obtained CuInS 2 films showed appropriate values for their application as an absorbing layer in photovoltaic structures of the type: glass/SnO 2 :F/CdS/Sb 2 S 3 /CuInS 2 /PbS/C/Ag. The whole structure was obtained through chemical bath deposition technique. The solar cell corresponding to 15 h of In 2 S 3 deposition duration bath showed energy-conversion efficiency (η) of 0.53% with open circuit voltage (V oc ) of 530 mV, short circuit current density (J sc ) of 2.43 mA cm -2 , and fill factor (FF) of 0.41. In the case of the structure with 24 h of deposition of In 2 S 3 bath, η = 0.43% was measured with the following parameters: V oc = 330 mV, J sc = 4.78 mA cm -2 and FF = 0.27. © 2014 Elsevier B.V. All rights reserved. 1. Introduction I–III–VI 2 ternary semiconductor compounds have been of great inter- est because of their potential application in the field of solar cells, light emitting devices, pigments, etc. [1]. Among the most studied of these semiconductor materials are CuInSe 2 [2], CuInS 2 [3] and AgInS 2 [4,5], because they are promising materials for photovoltaic applications, due to their suitable electrical and optical properties [6]. CuInS 2 films offer great advantages such as energy band gap (E g ) close to 1.5 eV at room temperature (in the optimal response zone for terrestrial photovoltaic conversion), high optical absorption coefficient in the visible region (10 5 cm -1 ), high thermal and electrical stabilities [7,8], high energy conversion efficiency in photovoltaic structures and low cost in the large area production [9]. This material has been applied in a solar cell prototype by Chen et al. [10]; the thin films of CuInS 2 were prepared by the deposition of Cu–In nanoparticles synthesized by a polyol method and chalcogenisation. The thin films were incorporated in the solar cell structure of the type: Mo/CuInS 2 /CdS/(i)-ZnO/SnO 2 :In/Ag showing the following values: open circuit voltage (V oc ) of 0.37 V, short circuit current density (J sc ) of 6 mA cm -2 , fill factor (FF) of 0.30 and energy-conversion efficiency (η) of 0.7%. Similarly, Nguyen et al. [11] used CuInS 2 films as ab- sorber layers, prepared by spray pyrolysis method, incorporated in struc- tures of the type: glass/SnO 2 :F/TiO 2 /In 2 S 3 /CuInS 2 /C, with: V oc = 0.50 V, J sc = 10.36 mA cm -2 , FF = 0.44 and η of 2.35%. Maier et al. [12] deposited the poly(3-(ethyl-4-butanoate)thiophene)/CuInS 2 :Zn nanocomposite on SnO 2 :In by spin-coating followed by thermal treatment at 180 °C, with the following results: V oc = 0.66 V, J sc = 1.4 mA cm -2 , FF = 0.27 and η of 0.4%. In the same way, Sandino et al. [13] fabricated a solar cell of the type: glass/Mo/CuInS 2 /ZnS/ZnO/Al depositing CuInS 2 films by co- evaporation and ZnS by chemical bath deposition (CBD); this solar cell showed an energy conversion efficiency of 5.4%. Other research groups have reported energy conversion efficiencies up to 12.5% [14], 11.4% [15] and 9.5% [16] with ternary material CuInS 2 as an absorbing layer. Thin films prepared by chemical methods are generally less expensive than those prepared by the capital-intensive physical techniques [17]. The CBD method as technique for the preparation of thin films has many advantages, which includes low cost of the required equipment and operation, simplicity, low energy consumption, and easily scalable to large area applications [18]. Up-to-date, CBD method has been widely used to deposit many different semiconductors thin films [17]. In this paper we reported the formation and characterization of thin films of CuInS 2 through the solid state reaction of In 2 S 3 –CuS stack films, heated at 350 °C during 1 h and their integration as an absorber layer in thin film solar cells, all prepared by CBD technique. Thin Solid Films 569 (2014) 76–80 ⁎ Corresponding author at: Av. Universidad S/N, Cd. Universitaria P.C. 66451, San Nicolás de los Garza, Nuevo León, México. Tel.: +52 81 8329 4000x6363. E-mail address: yolapm@gmail.com (Y. Peña). http://dx.doi.org/10.1016/j.tsf.2014.08.040 0040-6090/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf