Stack system of PECVD amorphous silicon and PECVD silicon oxide for silicon solar cell rear side passivation

A stack of hydrogenated amorphous silicon (a-Si) and PECVD-silicon oxide (SiOx) has been used as surface passivation layer for silicon wafer surfaces. Very good surface passivation could be reached leading to a surface recombination velocity (SRV) below 10cm/s on 1 Omega cm p-type Si wafers. By using the passivation layer system at a solar cell's rear side and applying the laser-fired contacts (LFC) process, pointwise local rear contacts have been formed and an energy conversion efficiency of 21.7% has been obtained on p-type FZ substrates (0.5 Omega cm). Simulations show that the effective rear SRV is in the range of 180 cm/s for the combination of metallised and passivated areas, 120 +/- 30 cm/s were calculated for the passivated areas. Rear reflectivity is comparable to thermally grown silicon dioxide (SiO2). a-Si rear passivation appears more stable under different bias light intensities compared to thermally grown SiO2.