Metal-sulfide assisted rapid crystallization of highly (001)-textured tungsten disulphide (WS2) films on metallic back contacts

Highly (001)-textured, photoactive WS2 films, which could be deposited before only on insulating substrates, have been prepared on polycrystalline metal layers, which can be used as back contacts for electronic WS2 devices, for instance for thin film solar cells. The WS2 films were prepared by the amorphous-solid-liquid-crystalline-solid (aSLcS) crystallization process from a Ni-S eutectic. However, normal polycrystalline metallic films can not be used as back contact layers, caused by the diffusion of the thin metal promoter (Ni) into the back contact layer, before a nickel-sulfur eutectic can be formed. Preventing the diffusion of the metal promoter into the back contact allows using the well-known metal-promoter assisted crystallization to grow photoactive films on different back contacts, like TiN:O. Additionally, WS2 films on tungsten layers could be grown by Ni-induced sulfidation of W films. Based on these experiments the model of the rapid nickel sulfide induced crystallization was modified: Ni assists the growth of WS2 crystallites already at temperatures between 500 and 600 C leading to WS2 films with differently oriented crystallites. At temperatures above the Ni-S eutectic temperature (637 C) liquid NiSx droplets induce, as reported earlier, a rapid recrystallization, which leads to WS2 films with strong (001) orientation. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)