Back surface cell structures for reducing recombination in CZ silicon solar cells

Abstract

Mass-produced terrestrial Czochralski (CZ) silicon solar cells are currently entering the domain in which bulk diffusion length is comparable to the cell thickness, so that recombination at the back surface can have a significant effect on device performance. Three manufacturable processes that address the problem of back recombination are examined here: boron diffusion from a deposited doped SiO2 layer[1]; Al-alloyed layers using screen-printed paste[2]; and use of a collecting n+ layer on the back interdigitated with the positive electrode[3,4]. 104-cm2 cells fabricated at Siemens Solar Industries using these back surface structures are characterized by current-voltage, spectral response, photoconductivity decay, and SIMS measurements.