CELLO photo-impedance-spectroscopy on PERC solar cells: Separation of bulk and rear surface defects

Thin PERC type solar cells are wait in the wings to take over from Al-BSF solar cells. However, the impact of (bulk) material and rear surface (contact) quality to the efficiency is found to be quite hard to measure on a processed solar cell. We will show with this paper that CELLO (solar cell local characterization) photo-impedance-spectroscopy measurements are capable of separating bulk from rear side effects on locally resolved maps. This allows cell manufacturers to better understand, analyze and control processing parameters and related defects like parasitic shunting, rear contact formation and passivation, gettering and other forms of degradation. As a result cell efficiencies and revenues can be boosted.