| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Tuesday Sessions |
| Session TF-TuP |
| Session: | Thin Films Poster Session |
| Presenter: | Irving Gonzalez, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Mexico |
| Authors: | I.J. Gonzalez, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Mexico I. Oliva Arias, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Unidad Mérida, Mexico |
| Correspondent: | Click to Email |
Zinc sulfide (ZnS) is a semiconductor material that has increased its importance in recent years due to its wide range of applications. For solar applications, ZnS has shown great potential as optical window for developing high efficiency CIGS solar cells. Chemical bath deposition (CBD) technique has been used for several years to obtain ZnS thin films. Deposition time, bath temperature and chemical reagents concentration are some parameters that have been investigated through time. However, there are scarce reports conducted to understand the physicochemistry of the CBD technique. In recent years, the development of physicochemical tools such as the species distribution diagrams (SDDs) and the solubility curves (SCs) gives light to understand the growth mechanisms to obtain the growth parameters for depositing high quality ZnS films. Nevertheless, most of these contributions have been carried out at temperatures between 60 and 90 °C leaving aside near ambient temperatures. Research on these conditions could bring benefits for industrial applications. This work aims to provide the physicochemical conditions in which high quality ZnS films at near ambient temperature can be obtained. A chemical bath containing ZnCl2, KOH, NH4NO3, and SC(NH2)2 as chemical reagents was used for depositing the ZnS films. Temperatures of 25, 40, and 55 °C were selected for films deposition. The SDDs and SCs were obtained for each temperature at three conditions (by varying [SC(NH2)2]) in order to study the influence of the chemical species onto the ZnS formation. The R=[HS-/]/[Zn(OH)22-] ratio as a main parameter for CDB-ZnS films deposition was investigated. The SCs show that higher values of R assure enough amount of HS- ions and better conditions for depositing ZnS, avoiding the formation of Zn(OH)2. The SDDs show that at near ambient temperatures the ZnS formation is attributed to the Zn(OH)3- and Zn(OH)42- complexes and the HS- ions.
ZnS films deposited onto glass substrates were characterized by x-ray photoelectron spectroscopy, atomic force microscopy, x-ray diffraction, and spectrophotometry techniques. Results indicate that when the R ratio and temperature are increased, better stoichiometry is obtained. The Zn is bonded mainly to hydroxide ions for lower R ratios, but when R increases bonding changes to S ions. The band gap energy of films was measured between 3.4 and 3.7 eV. The lower values are due to that samples contained ZnS and Zn(OH)2 because of the low value of R. ZnS films deposited at 55 °C presents a (111) cubic orientation (sphalerita); meanwhile, films deposited at 25 °C present an orthorhombic orientation due to the Zn(OH)2 formation.