Eliminating fine-grained layers in Cu(In,Ga)(S,Se)2 thin films for solution-processed high efficiency solar cells

Abstract

A non-hydrazine solution process has been considered as a promising way for the deposition of Cu(In,Ga)(S,Se)₂(CIGSSe) thin films. However, from our previous work, the presence of a fine-grained layer in the absorber layer was shown to be an obstacle to further improve the solar cell efficiency. Here, an improved fabrication route is proposed to solve this problem. A mixture of Cu₂S, In₂Se₃, Ga and Se was simultaneously dissolved in 1,2-ethanedithiol and 1,2-ethylenediamine, forming a homogeneous precursor solution to deposit CIGSSe nanocrystal films. By optimizing the selenization method by using rapid thermal processing (RTP) combined with an improved graphite box, large grains throughout the whole absorber layer were successfully obtained. Based on such a high-quality CIGSSe absorber layer, an encouraging power conversion efficiency of 11.8% has been achieved with a J_sc of 28.25 mA cm⁻², a V_oc of 596 mV and a FF of 69.79% and without an antireflection coating.