UV stability of highest-quality plasma silicon nitride passivation of silicon solar cells

The UV stability of Si solar cells passivated by low-temperature remote PECVD silicon nitride films is tested. Perfect stability of the front surface passivation and the rear surface passivation of both p-n junction as well as MIS-IL Si solar cells is observed. Using the microwave-detected photoconductance decay (MW-PCD) method, a very small and slow degradation of the differential effective surface recombination velocity S_eff.d is observed at silicon nitride-passivated p-Si surfaces corresponding to the nonmetallized rear surface regions of bifacial cells. However, the degradation is too small to have any impact on the long-term stability of encapsulated 17-18% rear efficient bifacial cells. Thin-silicon-oxide/silicon-nitride double layers incorporating Cs as used at the front surface of MIS-IL solar cells provide perfectly stable and excellently low differential S_eff.d values of 23 cm/s on 1.5-Ωcm wafers. Applied to the rear surface of bifacial Si solar cells, this double-layer scheme gives the potential of stable rear efficiencies of even 20%