Al–Si alloy point contact formation and rear surface passivation for silicon solar cells using double layer porous silicon

Abstract

Lowering the rear surface recombination velocities by a dielectric layer has fascinating advantages compared with the standard fully covered Al back-contact silicon solar cells. In this work the passivation effect by double layer porous silicon (PS) (wide band gap) and the formation of Al–Si alloy in narrow p-type Si point contact areas for rear passivated solar cells are analysed. As revealed by Fourier transform infrared spectroscopy, we found that a thin passivating aluminum oxide (Al2O3) layer is formed. Scanning electron microscopy analysis performed in cross sections shows that with bilayer PS, liquid Al penetrates into the openings, alloying with the Si substrate at depth and decreasing the contact resistivity. At the solar cell level, the reduction in the contact area and resistivity leads to a minimization of the fill factor losses.