International Journal of Science and Advanced Technology (ISSN 2221-8386) Volume 2 No 12 December 2012 http://www.ijsat.com 45 Influence of CdCl 2 Annealing Treatment on the Physical Properties of Chemical Bath Deposited CdS Thin Films J. Pantoja Enríquez*, G. R. Ibáñez Duharte, J. Moreira Acosta, L. A. Hernández, J. A. Reyes Nava Centro de Investigación y Desarrollo Tecnológico en Energías Renovables. Universidad de Ciencias y Artes de Chiapas. Libramiento Norte Poniente No 1150, 29039, Chiapas, México. e-mail: jpe2005@gmail.com G. Pérez Hernández Universidad Juárez Autónoma de Tabasco. Avenida Universidad S/N, Col. Magisterial, CP. 86040, Villahermosa, Tabasco, México P. J. Sebastian Centro de investigación en Energía-UNAM, Temixco, Morelos 62580, México. Abstract— Cadmium sulphide (CdS) thin films deposited onto glass substrates by chemical bath deposition (CBD) at 90 ºC were treated with a saturated solution of CdCl 2 and later annealed in air at temperatures of 350, 400 and 450 ºC for 60 minutes in order to investigate the influence of post- deposition annealing CdCl 2 treatments on the structural, optical and electrical properties. The structural parameters were investigated using XRD. The band gap of the films was calculated from the transmittance data. The electrical resistivity of the CdS films was measured at room temperature using the two-probe technique. The results showed that the structural, optical and electrical properties of CdS depend on the post-deposition annealing temperatures and CdCl 2 treatment. Keywords; Chemical bath deposition, CdCl 2 treatment, Cadmium sulphide, Thin films. I. INTRODUCTION Low series resistance, high transmittance and optimum band gap are very important requirements for CdS thin film to be considered a suitable window layer for solar cell. However, generally as deposited CdS thin films show high resistivity and optical transmittance, which can be improved. Post-deposition heat treatment is one of fundamental steps to improve the electrical and optical properties of CdS thin films. During the post-deposition heat treatments, fundamental structural changes happen for the film, which influence the optical and electrical properties of the semiconductor film and hence the device. Knowledge of the principal structural changes of the film during post-deposition treatments is very important in understanding and optimizing the performance of the photovoltaic device [1]. There are studies about the influence of heat treatments in different atmospheres on the physical properties of CdS thin films [2-12]. Hyeongnam Kim and Donghwan Kim [6] investigated the influence of the heat treatment on the microstructure of CdS and the performance of CdS/CdTe junctions. It was found that the annealing created pores in the chemically deposited CdS films; the performance of cells was improved after annealing CdS films; the CdS annealing time of 10 min was enough to obtain the optimum solar cell performance. No noticeable change in the optical transmittance and X-ray diffraction (XRD) patterns was observed after CdS annealing at temperature of 400, 450 and 530°C. H. Metin et al. [8] investigated the annealing effect on the structural, morphological, optical and electrical properties of the CdS films deposited on SnO 2 coated substrate. It was observed that the as-deposited and the film annealed at 423 and 523 K showed mixed phases dominated by cubic and hexagonal, respectively. The phase transformation from mix to pure stable hexagonal phase started at 623 K. The grain size of the films decreases from 45.67 to 28.30 nm with increasing annealing temperature, after that it increases from 41.00 to 141.00 nm when annealing temperature reaches to higher values of 623 K. The defects like dislocation density and strain in the films do not change regularly with increasing annealing temperature. The film annealed at 523 K shows the highest dislocation density (12.5×10 14 lines/m 2 ). Lei Wan et al. [10] annealed CdS films in air with or without a CdCl 2 coated layer. They concluded that: Air annealing without the CdCl 2 coating resulted in oxidation of the CdS films. The oxides of CdO and CdSO 4 presented on the CdS grain surface and at the grain boundaries. Lose of sulphur during annealing in air led to a significant sulphur deficiency. These two annealing effects hindered the coalescence and grain growth of CdS films when annealed in air without CdCl 2 pre-coating. The CdCl 2 coating protected the CdS films from oxidation during air annealing even at a temperature as high as 500°C. The anti-oxidation was attributed to the incorporation of a *Corresponding author (J. Pantoja Enríquez); e-mail: jpe2005@gmail.com