20% Efficient Screen-Printed Cells With Spin-On-Dielectric-Passivated Boron Back-Surface Field

This paper reports on the characteristics of a spin-on dielectric which has been used as the rear-surface passivation layer to achieve 20% efficient screen-printed (SP) boron back-surface field (B-BSF) solar cells. The dielectric provides, in a single thermal step, both stable passivation of a heavily doped p⁺ surface and strong gettering of iron which is a common contaminant in high-temperature boron diffusion processes. It was found that gettering of silicon substrates, contaminated during boron diffusion, is most effective when the dielectric is deposited on top of the boron-doped layer. The effect of dielectric charge density on passivation of p⁺ surfaces was also studied and a very high charge density of -10¹³ cm^-2 was found to be necessary to significantly improve the passivation on surfaces with a boron concentration.