Review of advanced hydrogen passivation for high efficient crystalline silicon solar cells

Hydrogen passivation, such as forming gas annealing and alneal (aluminum anneal) process, has been investigated for high efficient crystalline silicon solar cell structures, because the hydrogen atoms can reduce the surface recombination velocity. However, hydrogen could not diffuse deeply to passivate various defects within the silicon bulk. Further investigations into the properties of hydrogen in the silicon lead to the control of hydrogen atoms' charge states for their high diffusivity and reactivity. Also, research of the hydrogenated amorphous silicon nitride (a-SiNx:H) as a hydrogen source induced an 'advanced hydrogen passivation'. This paper provides a review of advanced hydrogen passivation applied on p-type, n-type and upgraded metallurgical grade crystalline silicon solar cells, respectively. Especially, the regeneration of boron-oxygen related defects, which cause carrier induced degradation, will be closely discussed since most of industrial solar cells are fabricated by boron-doped p-type silicon wafer. Moreover, laser-induced hydrogen passivation, which can locally recover defective area on the solar cells, will be addressed. In the conclusion, proper conditions of advanced hydrogen passivation for the successful improvement of minority carrier lifetime will be summarized.