In Situ Modulated PhotoLuminescence For Process Optimization Of Crystalline Silicon Passivation

Modulated Photoluminescence (MPL) is a powerful tool for measuring the minority carrier lifetime of solar cells. An in house in situ MPL equipped Plasma Enhanced Chemical Vapor Deposition reactor enables the monitoring of passivation properties of solar cells during the fabrication steps of devices. In this study, this tool was used to analyze the impact of annealing steps on passivation properties. First, samples passivated by an aluminum oxide layer were annealed and the evolution of the effective lifetime in the wafer was studied. This allowed to optimize the temperature and duration of the heat treatment. A similar study was made on Fired Passivating Contacts with a passivating stack of SiO
x
/(p)
$\mu\mathrm{c}$
-Si:H/SiN
x
:H. An interesting low-lifetime regime is consistently observed when the samples undergo a high temperature (
$\mathrm{T} > 350^{\circ}\mathrm{C}$
) annealing step, followed by a lifetime recovery during the subsequent cooling step. Corona charge and TEM images allowed to get a deeper understanding of the passivation mechanisms evidenced during in situ MPL measurements.