Molten salt route for ZnSe high-temperature electrosynthesis

Electrosynthesis appears as one of the best methods to prepare advanced mat erials under the form of coatings or thin layers. The advantages of such a process are economic (low investment for an easy composition control and la rge area deposition) and ecologic (no product loss). Yet, aqueous electroly sis exhibits two serious drawbacks: the low crystallinity of the electrodep osited material (due to the low working temperature) and the hydrogen disch arge (preventing electrodeposition of very electronegative elements as Ga). In this context, using high-temperature molten salts as electrolytes is a promising way to elaborate materials with tailored structures and propertie s. This method was successfully applied to the electrodeposition of the sem iconductor ZnSe which is a good candidate for window layers in thin film so lar cells. Electrochemical investigations performed in molten CaCl2-NaCl mi xture at 550 degrees C are reported. ZnSe was electrodeposited on glass she ets covered with SnO2. Optimized melt composition and potential led to yell ow, transparent and adherent thin films containing up to 90% well crystalli zed ZnSe with a ratio Zn/Se close to 1 and a 1-mm grain size. The energy ba nd gap measured is 2.5 eV. (C) 2000 Elsevier Science S.A. All rights reserv ed.