Wet Oxidation Effects on the Electrical and Interface Properties of ALD Al2O3 and ALD-AlOx/SiNx Passivation Stacks for PERC Solar Cells

32nd European Photovoltaic Solar Energy Conference and Exhibition; 660-663
We investigated the impact of wet oxidation on the electrical and interface properties of aluminum oxide (Al2O3) using atomic layer deposition (ALD) and aluminum oxide/silicon nitride (AlOx/SiNx) passivation stacks on silicon. Wet oxidation has been observed to have a significant effect on the field-effect passivation, showing an increase in the flat-band voltage shift (Vfb), and on the chemical passivation, which resulted in a reduction of the interface trap density (Dit). The decrease in Dit resulted in an increase in the lifetime and open-circuit voltages (Voc). This effect may be attributed to additional negatively charged traps originating from interstitial oxygen and hydrogen in the steam during wet oxidation. These results suggest that thermal annealing under ambient humidity is desirable to improve the quality of the passivation stacks on the rear side. This leads to high-performance passivated emitter rear cells (PERC).