Although the efficiency rating is lower than the efficiency records for the material class, the inkjet printing minimizes waste and offers industrial production benefits.

The drop-on-demand inkjet printing is a promising approach allowing patterning of materials with negligible materials waste and can reduce raw materials costs. Inkjet printing can also be easily adapted to a roll-to-roll process, which is suitable for large scale production. From the industrial application perspective, both of these two features of the inkjet printing technology are attractive. A critical requirement for using inkjet printing is to develop a suitable ink in terms of viscosity and stability which leads to compact and homogeneous films.

Dr. Xianzhong Lin from the Institute for Heterogeneous Material Systems of HZB used a molecular ink which was originally developed for spin coating technologies. The ink is produced by dissolving Cu, Zn, Sn metal salt and thiourea in dimethyl sulfoxide solvent. Lin tested the ink's suitability for inkjet printing and found that the viscosity of the ink can be tuned by adjusting the ink concentration and the ink composition can also be easily controlled by adding or reducing the amount of each chemical added. The CZTSSe absorbers were formed by annealing the inkjet-printed Cu-Zn-Sn-S precursor film under an atmosphere containing selenium.

Illustration of the working principle of inkjet printing. Credit: HZB