Low temperature contacting technique for improving rear surface passivation in silicon solar cells

A new rear contacting scheme using low temperature processes to form localised contacts without the use of photolithography has been developed. It uses randomly nucleated, aluminium induced, localised regions of solid phase epitaxial growth of p+ silicon onto the rear surface of a wafer through a thick rear surface passivating oxide. Results have shown that a suitable ohmic contact to the substrate can be formed through oxide as thick as 3000Angstrom and using only low temperature sintering below the eutectic temperature of silicon and aluminium. This low temperature sintering avoids the destruction of the interfacial oxide which has been shown to provide reasonable surface passivation for the rear of the substrate. Rear surface recombination can be controlled via the sintering time or temperature, which determines the dimensions for the localized regions of epitaxial growth.