Brunken, S.; Mientus, R.; Ellmer, K. : Photoactive Tungsten Disulfide (WS2) Nanosheets, Prepared by Rapid Crystallization from Liquid Sulfides. In: 24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany. München, 2010. - ISBN 3-936338-25-6, p. 363-365
We have shown, that photoactive, highly (001)-textured tungsten disulfide (WS2) films can be prepared both on insulating as well as metallic substrates. The WS2 films are crystallized from X-ray-amorphous WS3+x films by a rapid annealing process in an H2S atmosphere with the assistance of metal-sulfide droplets, which are formed, when the eutectic temperature in the system metal-sulfur is exceeded. As promoters Ni, Co and Pd can be used, where the eutectic temperatures with sulfur are in the range from 620 to 680 °C. From ex situ- and in situ-analysis a modified model for the formation of the WS2 nanosheets was derived, which resembles the well-known VLS (vaporliquid- solid)-model for the formation of nanorods (or whiskers), except that in our systems the precursor is also an (amorphous) solid, and instead of 1-dimensional rods, 2-dimensional nanosheets are grown. Especially, the preparation on metallic layers (W, TiN), which was not successful before, offers now the opportunity, to prepare thin film solar cells from these WS2 films. First experiments to prepare thin film solar cells show, that short circuits occur, most probably at grain boundaries, which have to be avoided or passivated.