Chemical Bath Deposition and characterization of CdS – PbS thin films.

Abstract

CdS–PbS thin films have been deposited on glass substrates by the chemical bath deposition technique. Cadmium sulphide thin layer was first deposited on glass substrate from a solution of cadmium chloride (CdCl₂) and thiourea (NH2CSNH2) with triethanolamine (TEA) as complexing agent. CdS – PbS films were obtained by depositing lead sulphide (PbS) films on the CdS – coated glass substrates from a solution of lead nitrate [Pb(NO₃)₂] and thioacetamide NH₃CSNH₂. Complexing agent again was TEA while in both cases aqueous ammonia (NH₃) created the necessary alkaline medium for the reaction to take place. The energy dispersive X – ray fluorescence (EDXRF) analysis confirmed the composition of the CdS and PbS thin films. Optical measurements were performed with a single-beam UNICAM Heλ 105 Spectrophotometer in the wavelength range of 195nm – 1000nm. The optical transmittance of CdS-PbS films is extremely low, in most cases zero within the UV and first half of the visible region but peaked at 49.4% (at λ = 994nm) for the 150^oC air-annealed samples and at 44.7% (at λ = 994nm) for the as grown samples in the near infra-red region. The absorbance is infinitely large in the UV and first half of the visible regions for both as-deposited films and annealed films, respectively but falls exponentially between the second half of the visible and near infra-red regions. The films have peak reflectance within the visible region. The films showed good characteristics for deployment not only as UV filters but also in solar control coating applications.

Keywords: Chemical bath, CdS, PbS, Thin Films, transmittance.