Influence of a Precursor Film with a Copper Gradient on the Properties of a Copper Indium Gallium Selenide Solar Cell

A precursor film with a Cu gradient was prepared in order to improve the quality of the absorber film produced by sputtering CIGS targets when using glass substrates. Two ceramic quaternary targets with different copper content were used for alternatively sputtering to get a bi-layer precursor film with a Cu gradient; meanwhile, the crystallization property and cell performance were studied. This was done in order to study the activities of the Cu element in the precursor layer before and after selenization. The film states of the temperature-rise period and high temperature selenization period were investigated. The appropriate structure of the precursor film was the Cu-rich layer underneath the Cu-poor layer. The Cu–Se phase, which is important for the crystalline property, can be produced in the Cu-rich layer under the heating period. The Cu-poor layer on the top reacts with the Cu-Se compound in the annealing process at a high temperature, and the big grain size of the absorber layer can be obtained due to Cu diffusion promoted by the gradient in the precursor film, as well as better conversion efficiency. This result shows that constructing the precursor film with a Cu gradient by sputtering different quaternary CIGS targets is a very promising fabrication method to obtain high-performance solar-cell devices with a good crystallization property under an annealing temperature of 550 °C and is suitable for further industrialized application.