High efficiency PERL cells on CZ P-type crystalline silicon using a thermally stable a-Si:H/SiNx rear surface passivation stack

For the purpose of manufacturing high efficiency p-type CZ crystalline silicon (c-Si) solar cells with conventional plated metallization and a passivated rear surface and local contacts, a thermally stable passivating system of plasma-enhanced chemical vapor deposition (PECVD) deposited a-Si:H/SiNx:H stack was developed in this work. Good thermal stability of this passivating stack capable of withstanding over 90 min thermal annealing at 400 °C enabled the implementation of hydrogenation processes to significantly enhance minority carrier lifetimes (τeff) in the bulk while simultaneously achieving compatibility with the metal contacting schemes that require relatively low sintering temperatures. Point local back surface field (LBSF) regions with effective surface recombination velocities (SRV) of less than 4800±400 cm/s were formed by laser-doping (LD) technique with optimized laser parameters on test wafers. The combination of the optimized a-Si:H/SiNx:H rear surface passivating stack, hydrogenation of the bulk and high quality LBSF formed by LD technique resulted in passivated emitter and rear locally diffused (PERL) cells with efficiency of up to 20.28% on a 13 cm2 industrial B-doped CZ silicon wafer. This is close to the record 20.3% efficient Pluto-PERL cells reported earlier this year and using the identically front surface designs. τeff of 1.7 ms with corresponding upperbound for the SRV of 5.8 cm/s was demonstrated with the same passivating stack on 1 Ω cm p-type FZ wafers.