Fabrication, characterization and application of Cu2ZnSn(S,Se)4 absorber layer via a hybrid ink containing ball milled powders

• CZTS powders are prepared from binary sulfides by a low cost ball milling process.
• Elaborated on phase evolution and formation mechanism of CZTS.
• Proposed a hybrid ink approach to resolve difficulty in deposition of CZTS film.
• CZTSSe solar cells with highest efficiency of 4.2% are fabricated.
• Small-grained CZTS layer hinders the collection of minority carriers.

Cu2ZnSnS4 (CZTS) powder with kesterite structure was prepared by ball milling of mixture of Cu2S, ZnS and SnS2 powders for more than 15 h. By dispersing the milled CZTS powder in a Cu-, Zn- and Sn-chalcogenide precursor solution, a hybrid ink was fabricated. With the hybrid ink, a precursor CZTS film was deposited on Mo coated soda-lime glass by spin-coating. In order to obtain Cu2ZnSn(S,Se)4 (CZTSSe) absorber film with kesterite structure, the CZTS film was annealed at 560 °C for 15 min in Se ambient. It is demonstrated that the annealed film is dominated by a thick layer of kesterite CZTSSe with larger grain size and Cu8Fe3Sn2(S,Se)12 impurity phase with the exception of a very thin layer of kesterite CZTS with smaller grain size at interface between the CZTSSe and Mo layers. Solar cell device was fabricated by using the annealed CZTSSe film as absorber layer, and its conversion efficiency reached 4.2%. Mechanism of formation of the kesterite CZTS powder and CZTSSe film as well as effect of impurity phases on conversion efficiency are discussed in the present paper. The present results suggest that the hybrid ink approach combining with ball milling is a simple, low cost and promising method for preparation of kesterite CZTSSe absorber film and CZTSSe-based solar cell.