Physical understanding of printed thick-film front contacts of crystalline Si solar cells—Review of existing models and recent developments

Existing models of the silver thick-film contact to an emitter are summarised and recent developments focusing on contact formation and current transport mechanisms are presented. As a glass layer exists at the silicon-thick-film interface the current transport mechanisms are not obvious. The main hypotheses are: current transport via spike-like direct silver–silicon interconnections or via tunnelling through the chemically modified glass layer. Recent investigations showed that silver crystallites grow into the emitter from the glass frit containing dissolved silver [G. Schubert, B. Fischer, P. Fath, in: Proceedings of photovoltaics PV in Europe Conference, Rome, 2002, pp. 343–346 [1]]. These silver islands are covered by a thin glass layer [C. Ballif, D.M. Huljic, A. Hessler-Wyser, G. Willeke, in: Proceedings of the 29th IEEE PVSC, Glasgow, 2002, pp. 360–363 [2]]. Further investigations are necessary to study the crystallite-growth mechanism as well as the current-transport mechanism from the crystallites to the finger.