Inkjet-printed CZTSSe absorbers and influence of sodium on device performance

Inkjet printing is a promising route for thin film deposition due to its low material wastage and potential of high throughput production. In this work, the inkjet printing technique is used for the deposition of Cu2ZnSn(SxSe1−x)4 (CZTSSe) thin films from Cu-Zn-Sn-S molecular inks. The key step for using the inkjet printing technique is to formulate a stable ink with suitable viscosity. The ink was prepared by dissolving Cu, Sn, and Zn metal salt precursors, thiourea and different amount of NaF (varied from 0 M to 1.12 M) in dimethyl sulfoxide. NaF was added to verify the influence of sodium (Na) in ink formation and CZTSSe device properties. It was found from the kesterite structure analysis that increasing NaF leads to segregation of a NaCl phase in the resulting CZTSSe films. Cross-sectional morphologies of the kesterite layer as revealed by scanning electron microscopy showed an enhancement from a multi-layered sandwich type to a double-layered structure by adding NaF. The photoelectron conversion efficiencies of solar cells, with a glass/Mo/CZTSSe/CdS/ZnO/AZO/Ni-Al configuration, increased from 1.7% to 6.4% with increasing NaF concentration from 0 M to 0.144 M and thereafter decreasing at higher NaF concentration (≥ 0.288 M).