Groschen – Plated Contacts – On the Way to Large-Scale Implementation

Silicon solar cell metallization is one important cost driver in industrial cell production. Plated contacts featuring copper as main conductor demonstrate great advantages over currently dominant silver screen printing technology. Important simplifications in the former process in conjunction with improvements of solar cell and module performance for plated cells have overcome limitations that hindered implementation of plating in the past. This makes plating an interesting option for all kinds of solar cells, including conventional and PERC devices. Optimizations at all stages of the process (laser ablation, pre-conditioning, plating, anneal) have enabled this progress and are still ongoing. Further great potentials are expected in plating technology that will be leveraged by this research.

Plated contacts for crystalline silicon solar cells feature a number of advantages over the current standard silver screen printing technique. Research in the field of plating for establishing contacts has been done since the early days of silicon PV, but it has so far only been implemented industrially in niche applications (e. g., interdigitated back-contact solar cells by SunPower, laser grooved buried contact solar cells by BP solar). For standard solar cells, the metallization process sequence has been too complex and costly to implement this technologically superior method in production up to now, despite important advantages in terms of material costs.

Simplifications at all stages of the process sequence (laser ablation, pre-conditioning, plating, anneal) have been enabled recently, also giving excellent cell- and module results. The project “Groschen” will extend theses developments and lay the groundworks for future industrial application of plating technology not only for high-efficiency solar cells, but also for standard BSF and PERC solar cells.

Advantages of plating are:

• low contact width down to 10 µm demonstrated with advanced laser technology
•  tuning of processes / materials according to solar cell requirements:
  • laser ablation with adhesion promoting substructure
  • nickel as  excellent electrical contact layer to even weakly p-type and n-type doped Si, and as diffusion barrier for copper
  • cheap, highly conductive copper (ρ= 1,7 x 10^-8 Ωm) as current transport layer (material cost reduction >90% compared to silver)
  • 100-200 nm thin silver layer for corrosion protection and soldering
• low contact recombination due to small contact area
• superior long-term stability expected (demonstrated in module tests under IEC conditions), insensitive to cell breakage
• industrial throughput machines available