Printing optimization and thermal sintering study of silver nano-ink for InkJet printing of solar electrodes using an industrial printhead

We present a successful inkjet printing capability for solar electrodes with line widths below 100 μm. A Theologically tailored conductive silver nano-ink was created to meet the rheological requirement of industrial printheads (XAAR 1001). The jetting optimization for the printhead was done using a desktop R&D inkjet printer from PiXDRO (OTB Solar). Printer-integrated software allowed the optimization of droplet formation and droplet stability during the jetting process. Typical printing parameters such as greyscale, DPI variation, substrate heating, etc., were optimized to achieve high print quality. However, initial printing results showed poor line definition and inhomogeneous film thickness. To overcome this, we developed a multiple pass printing process that results in excellent line definition. We also performed statistical analysis to correlate the droplet size with printed feature size. The minimum feature size of -15 μm was achieved by jetting ~6 pi droplets. After printing, the films were sintered thermally to achieve metallization. Detailed TGA study showed that complete metallization was achieved at temperature 400°C. Adhesion tests performed using an ASTM standard tape test on printed pattern showed less than 5% of delamination or flaking. Finally, test prototypes of solar front electrodes were printed successfully on ITO and silicon substrates.