Industrial relevant III-V/Si Back-end Processes - Update March, 2020

Nastaran Hayati-Roodbari, Roman Trattnig, Joanneum Research
March, 2020

Figure 1

Figure 2: Front side coating

Figure 3: backside coating Substrate: triple-junction solar cell-Azur space

Figure 4: Current density-voltage characteristic of an AZUR GaAs solar cell featuring inkjet-printed and laser sintered front-side contacts.

Figure 5

Figure 6: Primary results of aerosol jet printing showed very low contact resistivity of Cu ink on GaAs

Objectives and Status

Development of industrially scalable low cost processes for the front contact grid of the tandem solar cells, with Total series resistance of electrodes (contact resistance and bulk-resistance) < 1 Ohm cm² and less than 2% of the front side shaded area by electrodes.

To employ the back-end of the line (BEOL) processes developed in WP4 on solar cells, a defined layout was successfully inkjet-printed and sintered on different samples, followed by electroplating and etching steps. Afterwards, the cells were finished by coating of front anti-reflective layers and backside metallic contacts (Figure 3).
The current density-voltage (J-V characteristic) shows that the front contacts are well functional and a working solar cell could be achieved (Figure 4).
Furthermore, Aerosol-jet printing is considered as an alternative method for front side electrodes printing (seeding layer). The primary results showed very low contact resistivity of ionic ink on GaAs (< 10 mOhm cm²).
The application of the method is fast, therefore, optimization can be performed quickly. JR works on the required modifications of aerosol-jet printing and considers this method as an alternative for inkjet-printing.