Fabrication of silicon solar cells with rear pinhole contacts

A novel contacting technique has been demonstrated that involves low-temperature sinter of aluminium to form localised pinhole ohmic contacts through a silicon dioxide layer to the silicon substrate. A subsequent deposition of amorphous silicon and another low-temperature sinter allows solid-phase epitaxial growth of p+ silicon (Si) in the pinholes to achieve lower effective surface recombination velocities than the localised Al/Si interface. The technique has been demonstrated to allow ohmic contacts to be formed through oxide as thick as 3000 Å. This paper presents further developments of the contacting technique when applied on the back of buried contact solar cells. Higher fill factors (as high as 80%), improved open-circuit voltages (by 20–28 mV) and an increase of 7–12% in short-circuit currents have been achieved as a result. Initial analysis has revealed that heat treatment required for the formation of pinhole contacts or the epitaxial growth of p+ Si has a detrimental effect on the passivation quality of the oxide layer even in regions where no spiking has occurred. These findings indicate further improvement and optimisation of the contacting technique are possible.