Passivation of n-type emitter and p-type base in solar cells via oxygen terminated silicon nanoparticles

Various measurements and experiments are performed to establish the mechanism of passivation on emitter and base of conventionally manufactured solar cell with p-type base. The surface coatings on the emitter are removed. The bare surface is then coated with silicon (Si) nanoparticles (NPs) with oxygen termination. It shows an increase in the cell efficiency up to 14% over bare surface of solar cell. The NPs show enhancement in light scattering from the surface, but shows an increase in the recombination lifetime indicating an improved passivation. When back contact is partially removed, the coating on bare back side (p-type) of the solar cell also improves the cell efficiency. This is also attributable to the increased recombination lifetime from the measurements. Same NPs are seen to degrade the surface of n and p-type Si wafers. This apparently contradictory behaviour is explained by studying and comparing the emitter (n-type) surface of the solar cell with that of n-type Si wafer and the back surface (p-type) with that of p-type Si wafer. The emitter surface is distinctly different from the n-type wafer because of the shallow p-n junction causing the surface depletion. Back surface has aluminium (Al) metal trace, which plays an important role in forming complexes with the oxygen-terminated Si NPs (Si-O NPs). With these studies, it is observed that increase in the efficiency can potentially reduce the thermal budget in solar cell preparation. Copyright (c) 2013 John Wiley & Sons, Ltd.