Effect of Cd Concentration on Characteristics of CdS Thin Films Prepared by Chemical Bath Deposition

화학용액증착법에 의하여 증착된 CdS 박막의 특성에 대한 Cd 농도의 영향

  • Jung, SungHee (Department of Chemical Engineering, Inha University) ;
  • Chung, CheeWon (Department of Chemical Engineering, Inha University)
  • 정성희 (인하대학교 화학공학과) ;
  • 정지원 (인하대학교 화학공학과)
  • Published : 2012.08.10

Abstract

CdS thin films have been widely used as a buffer layer of CIGS semiconductor solar cells to reduce the lattice mismatch between transparent electrode and absorber layer. In order to prepare the CdS films with high transparency and low resistivity, they were deposited by varying Cd concentration with the constant S concentration in the solution using chemical bath deposition method. They were analyzed in terms of structural, optical and electrical properties of CdS films according to the $[S^{2-}]/[Cd^{2+}]$ ratio. In the case of Cd concentration higher than S concectration, CdS thin films were formed mainly by cluster- by-cluster formation due to the homogeneous reaction between Cd and S in the solution. Therefore the grain size increased and the transmittance decreased. On the other hand, in the case of Cd concentration lower than S concentration, CdS films were formed by heterogeneous reaction on the substrate rather than in the solution. The CdS films have the grains with the uniform circular shape of a few hundreds ${\AA}$. As the Cd concentration increased in the solution, the $[S^{2-}]/[Cd^{2+}]$ ratio decreased and the resistivity decreased by the increase in the carrier concentration due to the formation S vacancy by the excess Cd.

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