Compositional Dependence of Chemical and Electrical Properties in Cu₂ZnSnS₄Thin Films

Abstract

Photovoltaic-grade thin-film solar cell absorber layers composed of Cu 2 ZnSnS 4 are most often prepared under nonstoichiometric compositions, in particular Cu-poor and Zn-rich conditions. The effects of compositional deviations on chemical and electrical properties of this material are under investigation and are expected to have a strong influence on final device performance. Herein, a study of variation in the cationic ratios (Cu/Zn, Cu/Sn) across a broad range and their effect on the properties of thin films is presented. After etching to remove the ZnS phase, the ratio of Cu/Zn is nearly constant between all the films, while there are significant variations in the ratio of Cu/Sn. This is correlated with changes in the chemical and electrical properties of these films, as determined by variable temperature conductivity measurements. The postetching composition and absence of Sn-S secondary phases points to multivalency of Sn in this material, in addition to other potential factors such as differences in grain size and defect formation. The Cu/Sn ratio is shown to strongly affect the electrical properties of films, in particular of the conductivity, grain boundary barriers, and localization length. 2156-3381

Calculation of point defect concentration in Cu2ZnSnS4: Insights into the high-temperature equilibrium and quenching

“…18 Experimental structural analysis of the CZTS shows that the substitution of Cu atoms by Zn atoms significantly prevails in both Zn-rich/Cu-poor (A-type) and Cu-poor/Sn-poor (Btype) materials. 12,13 [44][45][46] is rather related to formation of the secondary phases than due to changes in concentration of the native point defects.…”

Microenvironment Created by SnSe2 Vapor and Pre‐Selenization to Stabilize the Surface and Back Contact in Kesterite Solar Cells

“…[50] However, due to a strong interaction between the Sn chemical equilibrium and selenization atmosphere, each slight change in processing conditions can lead to a considerable impact on the quality of the CZTSSe film and performance homogeneity over a larger area. [41,42,[51][52][53] Here, we demonstrate SnSe 2 vapor-assisted selenization as an effective method for fabricating high-quality kesterite semiconductors through a systematic investigation of the grain growth of Sn-rich and Sn-poor precursors by one-step and two-step selenization process, and by evaluating the photovoltaic properties. Rather than merely restraining Sn loss, the incorporation of SnSe 2 vapor in the selenization atmosphere can effectively modulate Sn content comprised in CZTSSe absorbers after the annealing process.…”

“…[ 50 ] However, due to a strong interaction between the Sn chemical equilibrium and selenization atmosphere, each slight change in processing conditions can lead to a considerable impact on the quality of the CZTSSe film and performance homogeneity over a larger area. [ 41,42,51–53 ]…”