High efficiency polycrystalline silicon solar cells using low temperature PECVD process

Conventionally directionally solidified (DS) and silicon film (SF) polycrystalline silicon solar cells are fabricated using gettering and low temperature plasma enhanced chemical vapor deposition (PECVD) passivation. Thin layer (/spl sim/10 nm) of PECVD SiO/sub 2/ is used to passivate the emitter of the solar cell, while direct hydrogen rf plasma and PECVD silicon nitride (Si/sub 3/N/sub 4/) are implemented to provide emitter and bulk passivation. It is found in this work that hydrogen rf plasma can significantly improve the solar cell blue and long wavelength responses when it is performed through a thin layer of PECVD Si/sub 3/N/sub 4/. High efficiency DS and SF polycrystalline silicon solar cells have been achieved using a simple solar cell process with uniform emitter, Al/POCl/sub 3/ gettering, hydrogen rf plasma/PECVD Si/sub 3/N/sub 4/ and PECVD SiO/sub 2/ passivation. On the other hand, a comprehensive experimental study of the characteristics of the PECVD Si/sub 3/N/sub 4/ layer and its role in improving the efficiency of polycrystalline silicon solar cells is carried out in this paper. For the polycrystalline silicon used in this investigation, it is found that the PECVD Si/sub 3/N/sub 4/ layer doesn't provide a sufficient cap for the out diffusion of hydrogen at temperatures higher than 500/spl deg/C. Low temperature (/spl les/400/spl deg/C) annealing of the PECVD Si/sub 3/N/sub 4/ provides efficient hydrogen bulk passivation, while higher temperature annealing relaxes the deposition induced stress and improves mainly the short wavelength (blue) response of the solar cells.