rEvolution – Plating Metallization Process for Back-Contact Back-Junction Solar Cells

Evolutionary Steps in the Cell Concept towards a Back-Contact Back-Junction Solar Cell

Duration: January 2013 - December 2015
Contracting Authority/ Sponsors: German Federal Ministry of Economic Affairs and Energy (BMWi)
Project Focus:
© Fraunhofer ISE

Fig. 1: Plated nickel copper contact of a back contact back junction solar cell. ©Fraunhofer ISE

© Fraunhofer ISE

Fig. 2: Microscope image of a plated front side contact on a Cz solar cell.

Plated metallization processes offer outstanding technical and economic perspectives for current as well as future solar cell concepts. At Fraunhofer ISE, this metallization concept was developed up to market maturity on p-type BSF and PERC solar cells. It has also been evaluated successfully on ten standard 60-cell solar modules with respect to finishing and long-term stability. We have derived processes for PERC, n-type, bifacial and back contact back junction solar cells from these processes. We were able to evolutionary advance the processes. With that, we were also able to pave the way for industrially completely new cell structures.

 

Already reliably established processes on current standard solar cells (Al-BSF, PERC) are the starting point for developments. Silver screen printing is replaced with laser structuring of the ARC with ultra-short ps pulses, followed by plated metallization with nickel, copper, and silver. This saves costs and opens up efficiency potentials of the cell, e. g. via a progressive emitter.

The same processes with minor adjustments are also used on n-type solar cells, where adjustments of the laser process to the changed passivation and of the plating step to the changed base polarity are required. With that, efficiencies of up to 21.7 % on small areas and up to 21 % on large areas could be achieved on PassDop solar cells.

Bifacial cells combine both requirements and offer twice the savings potential with respect to silver consumption. Here, the use of new process and system concepts makes sense. Existing knowledge of the base processes can be used in terms of an evolutionary development. We were able to demonstrate electroless plating and direct contacting of seed layers for simultaneous deposition on both polarities successfully.

For back contact back junction solar cells, plating processes - on the one hand - lend themselves to reinforcement of existing seed layers (PVD, screen printing) to save costs. On the other hand, a fully plated metallization can be realized in combination with suitable laser doping and ablation processes.