ZnS Buffer Layers: Novel Precursors for Aerosol-Assited Chemical Vapour Deposition

The efficiency of thin film solar technologies continues to increase; most notably, that of copper indium gallium selenide (CIGS) which has demonstrated lab-scale conversion efficiencies comparable with crystalline silicon-based solar cells.(1) Marketing such technology also provides an alternative to cadmium telluride thin films which have unavoidably toxic properties. The same hazards can be avoided via the deployment of zinc-based buffer layer materials, in replacement of the popular cadmium sulfide. Alloys of zinc oxide and zinc sulfide, Zn(O,S), exhibit a tuneable bandgap such to facilitate alignment with respective solar absorbers. This tunability requires control of Zn/S stoichiometry whilst also exercising high uniformity during fabrication, and given the intricate nature of thin film architectures, controllable and scalable fabrication methods must be considered. In this vein, chemical vapour deposition (CVD) is a viable technique for thin film deposition as single-source precursors can afford stoichiometric control. However, given their thermal sensitivity, single-source metal chalcogenide precursors are ill-suited for conventional CVD methods requiring volatile precursors. Instead, aerosol-assisted chemical vapour deposition (AACVD) presents an attractive deposition process which circumvents this criterion by atomizing a solution of the appropriate precursor.<br/>In this body of work, a novel single-source precursor design is explored as a basis for low-temperature deposition of metal chalcogenides via AACVD. A series of zinc thioamidate complexes is presented as potential precursors for the deposition of ZnS. Viability studies were conducted using thermogravimetric and NMR experiments. Viable precursor candidates give precedent for ZnO/ZnS co-deposition via AACVD for solar cell technology, and, more broadly, clean deposition of metal chalcogenide materials.<br/><br/>(1) M.K. Sobayel, M.S. Chowdhury, T. Hossain, H.I. Alkhammash, S. Islam, M. Shahiduzzaman, Md. Akhtaruzzaman, K. Techato, M.J. Rashid, Solar Energy, 2021, 224, 271-278.