Investigation of the back side passivation layer of screen printed bifacial silicon solar cells

Abstract

This work compares the back side passivation quality of bifacial silicon (Si) solar cells with boron back-surface-field (B-BSF) of different sheet resistances. The influence of the thickness of an additional dry thermal silicon dioxide (SiO2) to passivate the surface of the B-BSF is also investigated. The passivation quality is compared in two experiments: First Si lifetime samples with boron (B) emitter are passivated and their emitter saturation current densities (J0E) are determined with quasi-steady-state photoconductance (QSSPC) measurements after every process step. Secondly large area bifacial solar cells with different base doping are processed. The cell parameters are determined by illuminated current-voltage (IV) characteristics and the effective minority charge carrier diffusion lengths (Leff) are calculated with a model [1] using the internal quantum efficiencies (IQE) from spectral response measurements. The optimum B-BSF sheet resistance for the bifacial cell concept used is found to be 60 Ohm/sq. The optimum value of the thickness of the SiO2 layer for additional surface passivation is found to be in the range of 19- 30 nm dependent on the base doping.