Complete regeneration of BO-related defects in n-type upgraded metallurgical-grade Czochralski-grown silicon heterojunction solar cells

Abstract

Complete regeneration of boron-oxygen-related (BO) defects has been demonstrated on n-type upgraded metallurgical-grade (UMG) Czochralski-grown silicon heterojunction solar cells. Under accelerated regeneration conditions (93 suns, 220 °C), VOC fully recovered in 30-100 s and remained stable during a subsequent stability test. Under milder regeneration conditions (3 suns, 180 °C), the kinetics were slowed down by more than an order of magnitude, but the recovery of VOC was still complete and stable. The stabilized VOC of the UMG cells is 709 mV-722 mV, similar to the electronic-grade control cells. We conclude that a significant amount of hydrogen, sourced from the a-Si:H films and possibly the hydrogen plasma treatment, has been introduced into the bulk during the solar cell fabrication processes or the regeneration step. This results in abundant hydrogen concentrations in the bulk of the cells for the purpose of regeneration of BO defects, whether the cell was pre-fired with silicon nitride films (600 °C for 5 s) or not. Show more