Characterization of Al2O3 surface passivation of silicon solar cells

A study of the passivation of silicon surface by aluminum oxide (Al2O3) is reported. A correlation of fixed oxide charge density (Qf) and interface trap density (Dit) on passivation efficiency is presented. Low surface recombination velocity (SRV) was obtained even by as-deposited Al2O3 films and this was found to be associated to the passivation of interface states. Fourier transfer infrared spectroscopy spectra show the existence of an interfacial silicon oxide thin layer in both as-deposited and annealed Al2O3 films. Qf is found positive in as-deposited films and changing to negative upon subsequent annealing, providing thus an enhancement of the passivation in p-type silicon wafers, associated to field effects. Secondary ion mass spectrometry analysis confirms the correlation between Dit and hydrogen concentration at the Al2O3/Si interface. A lowest SRV of 15 cm/s was obtained after an anneal at 400 °C in nitrogen atmosphere.