Surface passivation of silicon solar cells using industrially relevant Al2O3 deposition techniques

By Jan Schmidt, Head of the PV Department, Institute for Solar Energy Research Hamelin (ISFH); Florian Werner, Institute for Solar Energy Research Hamelin (ISFH); Boris Veith, Researcher, Institute for Solar Energy Research Hamelin (ISFH); Dimitri Zielke, Institute for Solar Energy Research Hamelin (ISFH); Robert Bock, Institute for Solar Energy Research Hamelin (ISFH); Rolf Brendel, Director, Institute for Solar Energy Research Hamelin (ISFH); Veronica Tiba, Process Development Engineer, SoLayTec; Paul Poodt, Researcher, TNO Science & Industry; Fred Roozeboom, Senior Technical Advisor, TNO Science & Industry; Andres Cuevas, Professor of Engineering, The Australian National University (ANU); Andrew Li, The Australian National University (ANU)

The next generation of industrial silicon solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell, front and rear, is required. In the past, finding a suitable dielectric layer providing a high-quality rear passivation has been a major challenge. Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) has only recently turned out to be a nearly perfect candidate for such a dielectric. However, conventional ALD is limited to deposition rates well below 2nm/min, which is incompatible with industrial solar cell production. This paper assesses the passivation quality provided by three different industrially relevant techniques for the deposition of Al2O3 layers, namely high-rate spatial ALD, plasma-enhanced chemical vapour deposition (PECVD) and reactive sputtering.