GaAs compound-based electronics attracted significant interest due to unique properties of GaAs like high electron mobility, high saturated electron velocity and low sensitivity to heat. However, GaAs compound-based electronics demand a significant decrease in their manufacturing costs to be a good competitor in the commercial markets. In this context, copper-based nanoparticle (NP) inks represent one of the most cost-effective metal inks as a proper candidate to be deposited as contact grids on GaAs. In addition, Inkjet-printing, as a low-cost back-end of the line process, is a flexible manufacturing method to deposit copper NP ink on GaAs. These printed copper NP structures need to be uncapped and fused via a sintering method in order to become conductive and form an ohmic contact with low contact resistivity. The main challenge for uncapping a copper-based NP ink is its rapid oxidation potential. Laser sintering, as a fast uncapping method for NPs, reduces the oxidation of uncapped copper. The critical point to combine these two well-known industrial methods of inkjet printing and laser sintering is to adjust the printing features and laser sintering power in a way that as much copper as possible is uncapped resulting in minimum contact resistivity and high conductivity. In this research, copper ink contact grids were deposited on n-doped GaAs by inkjet-printing. The printed copper ink was converted to a copper grid via applying the optimized settings of a picosecond laser. As a result, an ohmic copper on GaAs contact with a low contact resistivity (8 mΩ cm2) was realized successfully.

This research study combines surface modification techniques with back‐end‐of‐line (BEOL) methods for cost‐effective, scalable front contact electrode deposition on III–V solar cells. Copper nanoparticle grids are deposited by inkjet printing on surface‐modified III–V solar cells. The deposition of a self‐assembled monolayer (such as 1,8‐octanedithiol) as an intermediate layer is a proven method for surface modification to improve the wettability of the substrate surface and the adhesion of the printed copper nanoparticle structures on the substrate to perform inkjet printing of coherent and narrow electrode structures. Then, the printed copper ink is converted to a conductive copper grid by a picosecond pulsed laser with optimized settings and an additional galvanic plating step is required for the thickening of inkjet‐printed and laser‐sintered seeding layer for solar cell applications. As a result, an ohmic copper contact on III–V layer with low contact resistivity (5 mΩ cm2) is realized successfully. The processed solar cell shows a functioning behavior with 20% conversion efficiency.

Epoxies are important thermoset materials with a broad range of applications. They are nominally homogeneous, have high strength and stiffness, but are brittle. In this work, we develop heterogeneous epoxies via additive printing with the goal of improving ductility, without compromising the strength and stiffness. To this end, we develop a reactive inkjet printing technology in which the resin and hardener components are printed successively using multinozzle printheads and which provides control of the local stoichiometric ratio. This allows creating epoxies with both in-plane and out-of-plane local compositional and mechanical heterogeneity. We print and test heterogeneous materials with several microstructural designs and demonstrate significant improvement of ductility, with retention of strength and stiffness. Furthermore, the properties of printed nominally homogeneous samples are close to isotropic and identical to those of the cast material of the same composition. The technology developed makes use of commercially available inks (resin and hardener); it is fully automated and provides sufficient flexibility and productivity to print complex macroscopic samples with 50 μm resolution of microstructural composition control.