Smart nano-inks for inkjet printing of functional oxide based thin films

The development of thin oxide based films for energy production and storage has been in the center of attention for the past decades. Performances of film based devices, such as solar cells, solid oxide fuel cells (SOFC), or sensors is strongly linked to the thickness of the active layers, with thinner layers often providing enhanced performances. The success in the development and usability of such energy production devices is linked to the deposition technique chosen for the layer
fabrication. The technique should be reproducible, industrially scalable and low cost to be viable as well as commercially attractive. Among thin film fabrication processes, inkjet printing is a high potential candidate.
Inkjet printing is a deposition method based on the jetting of very small droplets (approx. 10-12 l) onto substrates. It is a mask-less, non-contact additive patterning technique that allows the deposition of complex patterns with high positional accuracy of the droplets (typically in the micron-range spacing) with high speed and low cost. Due to these features, this processing method shows a strong potential as a thin film fabrication method. For the past decades inkjet printing of functional materials has been developed and studied as an alternative to spin coating, lithography, etching or physical vapor deposition technique such as pulse laser deposition (PLD) for the fabrication of metal oxide based thin films. One critical aspect in inkjet printing is the ink design and its long term stability. Instability can lead to undesirable nozzle clogging and unresolved printing that lower the global performance of the device.
This thesis presents the development and characterization of three inks designs which differs by the oxide source: a suspension of colloidal particles, a solution metallic precursor-based particle free ink, and a combination of both solution and suspension, here called hybrid ink. The major goal of this work was to evaluate the printability and the stability potentials of different ink designs for inkjet printing, and the pros/cons of each of them. The ink printability and stability is particularly evaluated through rheology, chemical characterization and droplet jetting observation. Films made of some relevant functional ceramics such as zirconium-, cerium-and titanium-oxide based materials are successfully fabricated with printers using different droplet ejection principles to demonstrate the versatility of the inks. Microstructure and performance of the films after heat treatment is characterized and show enhanced performance compared to films processed with different methods.