THE FORMATION OF LARGE-GRAIN CUINSE2 FILMS BY SELENIZATION BY HIGH-RATE SE TRANSPORT UNDER MODERATE VACUUM CONDITIONS

A novel method for forming large-grain CuInSe2 thin films by the reaction of In and Cu with Se inside a sealed ampoule is presented. A Se source and a selenization precursor consisting of a co-evaporated In+Cu film deposited onto an alumina substrate were placed at opposite ends of a closed quartz crucible sealed at 100 Torr. By establishing a small thermal gradient between the ends of the ampoule, Se was transported to the precursor where selenization of the In-Cu layer occurred. The maximum substrate temperature used was 475 degrees C. Resulting film microstructures were extremely well formed, consisting of 3 to 5 mu m grains of densely packed CuInSe2 crystallites. It is suggested that such enhanced grain growth may be the result of the preferential formation of the Serich liquid, L3, under conditions of high Se flux. Such a mechanism may be exploited for fabricating large-grain CuInSe2 films at temperatures compatible with substrates-of-choice in solar cell manufacturing.