Optimized amorphous silicon nitride layers for the front side passivation of c-Si PERC solar cells Asmaa Mohamed Okasha Mohamed Okasha, Bishal Kafle, Benjamin Torda, Christopher Teßmann and Marc Hofmann EPJ Photovolt., 11 (2020) 6 Published online: 29 May 2020 DOI: 10.1051/epjpv/2020003