Impact of the firing step on Al2O3 passivation on p-type Czochralski Si wafers: Electrical and chemical approaches

The development of an efficient surface passivation is a key feature of silicon solar cells towards the improvement of €/W ratio. An Al2O3 layer coated by plasma-enhanced atomic layer deposition has proven its efficiency to increase the minority carrier lifetime on p-type silicon. However, the firing step, which is a common part of the manufacturing process that includes metallic pastes for screen-printed contacts, ruins this passivation effect. On the basis of photoelectric, electric, and chemical experimental studies, a correlation is provided in this paper between the different microscopic and macroscopic behaviors that govern the passivation process. To show this correlation, photoconductance decay measurements have been carried out to determine minority carrier lifetime. Following which, the capacitance–voltage measurement results are used to extract electrical parameters, namely, the densities of interface defects and effective charges. In addition, complementing secondary ion mass spectrometry (SIMS) experiments revealed the different chemical species that can be relevant for the explanation of passivation quality and macroscopic electrical measurements.