The surface passivation properties of aluminium oxide (Al 2O 3) on crystalline Si are compared with the traditional passivation system of silicon nitride (SiN x). It is shown that Al 2O 3 has fundamental advantages over SiN x when applied to the rear of p-type silicon solar cells as well as to the p + emitter of n-type silicon solar cells. Special emphasis is paid to the transfer of Al 2O 3 into industrial solar cell production. We compare different Al 2O 3 deposition techniques suitable for mass production such as ultrafast spatial atomic layer deposition, inline plasma-enhanced chemical vapour deposition and reactive sputtering. Finally, we review the most recent cell results with Al 2O 3passivation and give a brief outlook on the future prospects of Al 2O 3 in silicon solar cell production.