Regular Article

Model for contact formation of novel TeO₂ containing Pb-free silver paste on n⁺ and p⁺ doped crystalline silicon

¹ University of Konstanz, Department of Physics, 78457 Konstanz, Germany
² Johnson Matthey Technology Centre, Sonning Common, Reading, RG4 9NH, UK

^* e-mail: fabian.geml@uni-konstanz.de

Received: 1 July 2022
Received in final form: 8 October 2022
Accepted: 16 December 2022
Published online: 7 February 2023

Abstract

Silver (Ag) pastes are widely used in the global market for most solar cell architectures. Thereby, lead (Pb) is no longer wanted in productions for environmental reasons. In this work, a model for the contact formation between Pb-free, tellurium oxide (TeO₂) containing screen-printable Ag pastes and silicon is presented. It is shown that Te plays a key role in this model. Te is not only an important part in etching the surface passivation layers with TeO₂ dissolving the dielectric layer but also for a formation of the contacts with Te forming a compound consisting of Ag₂Te. Using EDX mapping, local contact regions can be examined and interpreted for contact formation. The used paste system enables far more flexible paste mixturing leading to a novel developed commercial paste which is on a par with other pastes used in industry concerning the resulting contact properties. This is also demonstrated in this work by the very low contact resistivity of less than 1 mΩcm² over a wide range of firing peak temperatures. It is additionally shown that good resistivities can be achieved on both n⁺- and p⁺-doped regions.