Analysis of the SiO2 passivation of the rear and front surface of solar cells with selective back surface field

ABSTRACT The silicon solar cell passivation is essential to achieve high efficiency, because reduces the minority charge carrier recombination. The SiO2 growth is the most effective technique to passivate crystalline silicon wafers. The goal of this paper is to present the development and analysis of the rear and front passivation with different thicknesses of SiO2, grown by dry oxidation. Solar cells were processed with selective back surface field (BSF) in solar grade p-type Czochralski-grown wafers. The front emitter was produced by phosphorus diffusion and the selective BSF was formed by boron and aluminum diffusion to allow the passivation also in the rear face. The oxidation temperature (Toxi) and time (toxi) were ranged to form SiO2 layer with different thicknesses. Based on previous studies, the Toxi was kept at 800 °C and the toxi was ranged from 2 minutes to 90 minutes. In the next step, the Toxi was ranged from 770 °C to 920 °C for the toxi = 7 minutes. The thicknesses of the SiO2 layer ranged from 7 nm to 80 nm in the front emitter and from 1 nm to 14 nm in the rear face. The open circuit voltage (Voc) was compared to evaluate the passivation and this parameter increased up to toxi = 45 minutes and up to Toxi = 860 °C. Based on these results, the oxidation time was ranged for Toxi = 860 °C. The higher Voc, of 604 mV, was obtained for: Toxi = 860 °C and toxi = 30 minutes and b) Toxi = 800 °C and toxi = 45 min, resulting in a SiO2 layer of around 50 - 60 nm and of 10 - 14 nm in the phosphorus and boron doped face, respectively. The highest achieved efficiency was of 16.0 %.