20% efficient screen printed boron BSF cells using spin-on dielectric passivation

This paper reports on the characteristics of a negatively charged spin-on dielectric which has been used as the rear surface passivation layer to achieve 20% efficient screen-printed boron back surface field (B-BSF) solar cells. Solar cell schemes which utilize a heavily doped boron back surface field often face the challenges of avoiding wafer contamination during a long, high-temperature diffusion process and achieving good surface passivation of the heavily doped surface. The dielectric examined in this work addresses these challenges as it provides both impurity gettering and surface passivation in a single thermal step. Gettering studies have been performed to compare POCl₃ and dielectric gettering and to examine the relationship between gettering strength and the proximity of the gettering site to the doped layer. Passivation and charge density studies have been used to identify the passivation mechanism and to examine the stability of the dielectric passivation.