Development and Characterization of Surface Passivation Materials on Silicon Wafers for Solar Cells
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A main challenge for high efficiency crystalline silicon solar cells is to reduce the current and voltage loss from the surface recombination process. An effective surface passivation system is needed to obtain high performance solar cells, and passivation materials based on industrial system could be preferred for their implementation in the PV industry. In order to obtain a stable and high quality passivation system, the passivation properties of different materials need to be studied. In this thesis, several passivation systems have been investigated in terms of their passivation properties, i.e. electrical-, chemical-, thermal- and light stability. Considering cost effectiveness as well as material passivation properties, plasma enhanced chemical vapor deposition (PECVD) deposited amorphous silicon, amorphous silicon and silicon nitride stacks, and silicon oxynitride and silicon nitride stacks have been studied on their thermal, electrical and chemical properties on silicon substrates. Furthermore, in order to approaching the theoretical limit of c-Si solar cell, developing more materials for silicon surface passivation is also important. The surface passivation properties of hafnium oxide deposited by atomic layer deposition on n-type silicon wafers have been explored from basic deposition parameters, including pre-cleaning, precursors, deposition temperature as well as annealing process. Nearly 2 ms effective lifetime has been obtained on hafnium oxide passivated samples with low interface defect density and high negative charges. Moreover, the light stability of hafnium oxide passivation has been tested and it shows lifetime enhancement under light, which is good for solar cell device. It has been proved that hafnium oxide could be a promising candidate for silicon surface passivation. In conclusion, these results indicate that materials based on PECVD deposition can be good candidates for the modern silicon solar cell industry. The explorations of passivation properties of new materials give alternative choice for surface passivation for high efficiency silicon solar cell.