Effects of pH on the characteristics of ZnS thin films grown by using the CBD method*

In CIGS-based thin film solar cells, a chemically deposited ZnS buffer layer with high resistivity is generally used between the absorber layer and transparent conducting oxide layer. In this work, we report a chemical process to prepare ZnS films by the CBD technique based on the typical bath deposition. The influences of ammonia (NH$_{\mathrm{4}}$OH) and Na$_{\mathrm{2}}$EDTA (Na$_{\mathrm{2}}$C$_{\mathrm{10}}$H$_{\mathrm{16}}$N$_{\mathrm{2}}$O$_{\mathrm{8}})$ as complexing agents on structural, morphological, and optical properties of ZnS thin films are investigated ranging pH concentration from 5 to 10. To investigate effects of pH on the characteristics of ZnS thin films, by using UV-visible transmittance, atomic force microscopy, and optical absorption were investigated. With changing the pH range, the ZnS thin films demonstrate high transmittance of 75\textasciitilde 80{\%} in the visible region, indicating the films are potentially useful in photovoltaic applications. The results will be presented in detail.