PECVD SiNx induced hydrogen passivation in string ribbon silicon [solar cells]

To improve the bulk minority carrier lifetime in string ribbon silicon, SiN_x induced defect passivation during a post deposition anneal is investigated. The authors´ results indicate that SiN_x induced hydrogen passivation is very effective when the SiN_x film is annealed in conjunction with a screen-printed Al layer on the back. In addition, it is found that controlled rapid cooling can be used to enhance the defect passivation process. A model is proposed which relates the high temperature passivation to the release of hydrogen from the SiN_x film, the injection of vacancies from backside Al alloying, and the retention of hydrogen at defect sites. High efficiency screen-printed string ribbon solar cells (>14.5%) are fabricated utilizing the simultaneous SiN_x/Al anneal in a belt furnace for hydrogenation and Al-BSF formation, followed by RTP firing of screen-printed contacts to improve the retention of hydrogen at defects