Advanced Hydrogenation of Dislocation Clusters and Boron-oxygen Defects in Silicon Solar Cells

Abstract

Advanced hydrogenation processes targeting the generation of neutrally charged hydrogen (H°) are applied to passivate structural defects in seeded-cast quasi mono-crystalline silicon wafers and boron-oxygen defects in Czochralski silicon. The application of a one minute laser hydrogenation process onto a finished screen printed solar cell fabricated on the dislocation-rich seeded-cast material resulted in efficiency enhancements of 0.6% absolute through improvements in the implied open circuit voltage and internal quantum efficiency in the vicinity of the dislocated regions. A new insight is presented on the formation of boron-oxygen defects with a strong dependence on illumination intensity. An advanced laser hydrogenation process is presented to rapidly form and hydrogenate boron-oxygen defects simultaneously, in an 8 s process applied directly after belt furnace firing, with the hydrogenation of more than 95% of boron-oxygen defects at a peak temperature of approximately 360°C on lifetime test structures. The same 8 s process is also demonstrated on standard screen-printed solar cells applied directly after belt furnace firing to simultaneously form- and hydrogenate the boron-oxygen defects, with no subsequent loss in electrical performance, hence avoiding a 0.7% absolute loss in efficiency due to light-induced degradation.