The alloy formation between physical vapor deposited Al and Si at the rear side of the industrially applicable passivated emitter and rear solar cell has been investigated. New insights of sequential phases and phenomena like escape of gaseous bubbles from the melt and reduced surface wetting as a function of the applied temperature profile are documented by in situ light-microscopic observation. A cross-sectional analysis of the local contact formation is performed using scanning spreading resistance microscopy. During the melting phase, the interaction of Al and Si at locally opened areas in a dielectric layer stack, as well as the interaction between Al–Si melt and the dielectric layers is recorded with a video camera and analyzed. It was found out that the SiOx layer reacts with the Al–Si melt and that SiNy layer plays a fundamental role for the correct isolation of the solar cells.
Typical shape of a locally alloyed Al–Si/Al-BSF (back surface field) point contact in an i-PERL Si solar cell with laser-ablated openings in a dielectric stack that separates the Al cover layer from the Si bulk of the wafer.