Demystifying the effect of hydrogen treatment on silicon photovoltaics

Interactions between hydrogen and silicon play an integral role in determining the quality of surface and bulk passivation of various device structures in silicon photovoltaics. The efficacy of a hydrogen treatment method is known to be dependent on whether the interacting hydrogen species is atomic, ionic, or molecular. Furthermore, these concentrations can be altered by controlling the substrate temperature of the silicon substrate. Moreover, an important consideration is the time and atmosphere the treatment is carried out in, as it influences the desorption of hydrogen from silicon. Hence, it is important to undertake a comprehensive investigation of both the theoretical and experimental aspects of hydrogen passivation of silicon devices, thereby developing a clear understanding of how hydrogen behaves within different solar cell structures, and its dependence on substrate properties. In the theoretical study presented, we assume that the total concentration of hydrogen in the silicon substrate does not remain constant when temperature is increased, and that longer exposures to higher temperatures may cause further loss of hydrogen. This will be augmented by experimental studies of a-Si passivation layers on silicon subjected to hydrogen treatments and follow-on stepwise annealing with resulting loss of hydrogen and examination of its effect on the minority carrier lifetime.