Uniform coating of light-absorbing semiconductors by chemical bath deposition on sulfide-treated ZnO nanorods

ZnO nanorod films are increasingly used as an alternative to nanoporous TiO₂ as the electron conductor in semiconductor-sensitized nanoporous solar cells (SSSCs). Semiconductor light absorbers deposited onto ZnO by chemical bath deposition (CBD) tend to form poorly covering deposits of isolated clusters. We show how a short solution pretreatment of the ZnO nanorod films with a sulfide solution, which forms a thin ZnS film at the ZnO surface, results in a very large improvement of the coverage and uniformity of the CBD semiconductor coatings. These composite films give large improvements in solar cell efficiency. Several factors can be responsible for this improvement: better coverage of the ZnO nanorods, less shorting between hole conductor and conducting substrate, and the formation of a ZnS buffer layer.