Direct Contact Electroplating Sequence Without Initial Seed Layer for Bifacial TOPCon Solar Cell Metallization

Benjamin Grubel,Varun Arya,Norbert Bay,Michael Passig,Christian Schmiga,Sven Kluska,Markus Glatthaar,Bernd Steinhauser,Gisela Cimiotti,Damian Brunner

doi:10.1109/jphotov.2021.3051636

Abstract

The metallization of bifacial tunneling oxide and passivating contacts (TOPCon) solar cells without initial metal seed layer by electroplating of Ni/Cu/Ag is demonstrated. The presented approach allows a lead-free metallization with narrow contact geometries and low contact resistivity. A metal plate provides electrical contact to the silicon via micrometer size laser contact openings and allows electroplating of bifacial TOPCon solar cells using industrial type inline plating tools without the need of a previously applied seed layer. Challenges such as direct contacting of silicon and dissolution of contacts are identified, and potential solutions are discussed. An optimized process sequence is developed and with this approach a solar cell efficiency of 22.5% is demonstrated on industrial bifacial TOPCon solar cells reaching the same level as the screen-printed reference solar cells.

Highlights

S OLAR cells featuring carrier selective contacts such as tunneling oxide and passivating contacts (TOPCon) consisting of a thin oxide layer and a highly doped poly-Si, which significantly reduces contact recombination have attracted an increased interest lately
We present a new plating process sequence for bifacial TOPCon solar cells omitting the necessity of a conductive seed layer by contacting directly the silicon within laser contact openings
The presented plating sequence for bifacial TOPCon solar cells consists of plating the full Ni/Cu/Ag stack on one side of a solar cell followed by plating of the same metal stack on the opposite side

Summary

INTRODUCTION

S OLAR cells featuring carrier selective contacts such as tunneling oxide and passivating contacts (TOPCon) consisting of a thin oxide layer and a highly doped poly-Si, which significantly reduces contact recombination have attracted an increased interest lately. We present a new plating process sequence for bifacial TOPCon solar cells omitting the necessity of a conductive seed layer by contacting directly the silicon within laser contact openings. This approach was introduced by Gensowski et al [13] as direct contact plating. State-of-the-art single sided plating tools such as inline plating tools were used in this work to demonstrate direct contact plating for bifacial TOPCon solar cells

Approach and Plating Conditions

Solar Cells

IV Results

Direct Contact Plating

Contact Modifications due to Electrolyte Wrap-Around

CONCLUSION