Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure Surface recombination velocities (SRVs) below 10 cm/s on p-type crystalline silicon wafers passivated by atomic-layer-deposited (ALD) aluminium oxide (Al2O3) films of thickness >= 10 nm. For films thinner than 10 nm the SRV increases with decreasing Al2O3 thickness. For ultrathin Al2O3 layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Omega cm p-Si and an exceptionally low SRV of 1.9 cm/s on high-resistivity (200 Omega cm) p-Si. Ultrathin Al2O3 films are particularly relevant for the implementation into solar cells. as the deposition rate of the ALD process is extremely low compared to the frequently used plasma-enhanced chemical vapour deposition of silicon nitride (SiNx) Our experiments oil silicon wafers passivated with stacks composed of ultrathin Al2O3 and SiNx show that a substantially improved thermal stability during high-temperature firing at 830 degrees C is obtained for the Al2O3/SiNx stacks compared to the single-layer Al2O3 passivation. Al2O3/SiNx stacks are hence ideally suited for the implementation into industrial-type silicon solar cells where the metal contacts are made by screen-printing and high-temperature firing of metal pastes (C) 2009 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim