Nano-crystalline thin films of lead chalcogenides (PbS, PbSe and PbTe) were deposited on transparent conducting oxide (TCO) coated glass substrates using a simple galvanic technique. The basic electrochemical cell consisted of a Pb strip as a self-decaying anode, with TCO coated glass substrate as the cathode and a Pb(CH₃COO)₂ solution. Na₂S₂O₃, H₂SeO₃ and HTeO₂⁺ were introduced in the cell for PbS, PbSe and PbTe thin film depositions, respectively. No external bias was applied for the depositions; instead, the two electrodes were short circuited externally by a copper wire. The deposition potential was achieved from the difference in the electrode potentials. The Pb²⁺ was complexed to Pb-EDTA in all the cases, so that, no other Pb salts are precipitated through chemical reactions. A pH of 3 for the working solution was found to be optimum for all the depositions. Depositions were carried out at room temperature, without stirring of the solution. The following are the cathode reactions for the three electrochemical processes:

For PbS:

At cathode: Pb²⁺ + 2e → Pb, S₂O₃^2- + 6H⁺ + 4e → 2S + 3H₂O

Overall: 2Pb²⁺ + S₂O₃^2- + 6H⁺ + 8e → 2PbS + 3H₂O

For PbSe:

At cathode: Pb²⁺ + 2e → Pb, SeO₃^2- + 6H⁺ + 4e → Se + 3H₂O

Overall: Pb²⁺ + SeO₃^2- + 6H⁺ + 6e → PbSe + 3H₂O

For PbTe:

At cathode: Pb²⁺ + 2e → Pb, HTeO₂⁺ + 3H⁺ + 4e → Te + 2H₂O

Overall: HTeO₂⁺ + Pb²⁺ + 3H⁺ + 6e → PbTe + 2H₂O

The anodic reaction Pb → Pb²⁺ + 2e is the same for all the three cases.

X-ray characterization revealed that PbS, PbSe and PbTe thin films were all of cubic phase. The formation of nano-crystallites with dense and compact surface morphology was detected from FESEM and AFM measurements. EDX analysis showed metal deficient compositions, indicating p-type nature of the films. The nano-crystalline films showed ‘blue shifted’ IR absorption, which changed to bulk values when the crystallites were allowed to grow large. The nature of the n-TCO/p-PbX (X = S, Se, Te) hetero-junction has been studied.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/11498 must be provided.

1. A green approach towards deposition of CdS thin films by an electrochemical technique