Fabrication of ZnSnP2 thin films by phosphidation

• We fabricated ZnSnP2 thin films as a solar absorber by phosphidation method.
• We clarified the mechanism of morphology change during the phosphidation.
• We demonstrated the utility of potential diagrams through the ZnSnP2 growth process.

ZnSnP2 is a promising candidate as a solar absorbing material consisting of earth-abundant and low-toxic elements. In this study, the phosphidation method, where co-sputtered Zn–Sn thin films react with phosphorus gas, was adopted for fabricating ZnSnP2 thin films. To establish the conditions for producing ZnSnP2 thin films, we investigated the influence of phosphidation temperature on the product phases, and interpreted the experimental results using chemical potential diagrams of the Zn–Sn–P system. ZnSnP2 thin films with a single phase were obtained by phosphidation at 500 °C under a phosphorus vapor pressure of 10− 2 atm. However, formation of ZnSnP2 protrusions was observed on the surface of the thin films. Based on the experimental results and the chemical potential diagrams, it is indicated that un-reacted liquid Sn particles reacted with Zn and phosphorus gas to form ZnSnP2 protrusions in a manner similar to the vapor-Liquid-Solid growth mode.