HIGH-EFFICIENCY POLYCRYSTALLINE SILICON SOLAR-CELLS USING LOW-TEMPERATURE PECVD PROCESS

Conventionally directionally solidified (DS) and silicon him (SF) poly crystalline silicon solar cells are fabricated using gettering and low temperature plasma enhanced chemical vapor deposition (PECVD) passiva tion. Thin layer (similar to 10 nm) of PECVD SiO2 is used to passivate the emitter of the solar cell, while direct hydrogen rf plasma and PE CVD silicon nitride (Si3N4) are implemented to provide emitter and bul k passivation, It is found in this work that hydrogen rf plasma can si gnificantly improve the solar cell blue and long wavelength responses when it is performed through a thin layer of PECVD Si3N4. High efficie ncy DS and SF polycrystalline silicon solar cells have been achieved u sing a simple solar cell process with uniform emitter, Al/POCl3 getter ing, hydrogen rf plasma/PECVD Si3N4 and PECVD SiO2 passivation. On the other hand, a comprehensive experimental study of the characteristics of the PECVD Si3N4 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 th at the PECVD Si3N4 layer doesn't provide a sufficient cap for the out diffusion of hydrogen at temperatures higher than 500 degrees C. Low t emperature (less than or equal to 400 degrees C) annealing of the PECV D Si3N4 provides efficient hydrogen bulk passivation, while higher tem perature annealing relaxes the deposition induced stress and improves mainly the short wavelength (blue) response of the solar cells.