Passivation of aluminium-n+ silicon contacts for solar cells by ultrathin Al2O3 and SiO2 dielectric layers

Ultra-thin thermally grown SiO2 and atomic-layer-deposited (ALD) Al2O3 films are trialled as passivating dielectrics for metal-insulator-semiconductor (MIS) type contacts on top of phosphorus diffused regions applicable to high efficiency silicon solar cells. An investigation of the optimum insulator thickness in terms of contact recombination factor J(0_cont) and contact resistivity (c) is undertaken on 85 / and 103 / diffusions. An optimum ALD Al2O3 thickness of approximate to 22 angstrom produces a J(0_cont) of approximate to 300 fAcm(-2) whilst maintaining a (c) lower than 1 m cm(2) for the 103 / diffusion. This has the potential to improve the open-circuit voltage by a maximum 15 mV. The thermally grown SiO2 fails to achieve equivalently low J(0_cont) values but exhibits greater thermal stability, resulting in slight improvements in (c) when annealed for 10 minutes at 300 degrees C without significant changes in J(0_cont). The after-anneal J(0_cont) reaches approximate to 600 fAcm(-2) with a (c) of approximate to 2.5 m cm(2) for the 85 / diffusion amounting to a maximum gain in open-circuit voltage of 6 mV. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)