Incorporation of selenium ions in solution-processed Cu(In,Ga)Se2 films

Cu(In,Ga)Se-2 films were prepared on the molybdenum-coated soda-lime substrate using various processes to incorporate selenium ions. Selenium ion-containing solutions and selenium vapor were both used as the sources of selenium. When the precursors of Cu(In,Ga)Se-2 were coated with selenium ion-containing solutions, the formation of MoSe2 was detected via secondary ion mass spectroscopy and GIXD analysis. The formation of thick MoSe2 films tended to retard the formation of Cu(In,Ga)Se-2 and reduced the grain size of the prepared films. Therefore, the thick MoSe2 layer led to a decrease in the fill factor and the short-circuit density of the fabricated Cu(In,Ga)Se-2 solar cells. The selenium ion-containing solutions were found to be easily evaporated during the heating process, thereby resulting in a decrease in the thickness and the porous microstructures of films. The decrease in the thickness of Cu(In,Ga)Se-2 led to the decrease in the fill factors and the short-circuit density of the fabricated devices. The efficiency of Cu(In,Ga)Se-2 solar cells prepared via selenium vapor was higher than that prepared via selenium ions. The photovoltaic characteristics of the fabricated solar cells were demonstrated to depend substantially on the routes of supplying and incorporation of selenium ions at elevated temperatures.