20% Efficient Screen-Printed n-Type Solar Cells Using a Spin-On Source and Thermal Oxide/Silicon Nitride Passivation

N-type Si cells offer a compelling alternative to p-type cells to achieve high, stabilized cell efficiencies because they do not suffer from light-induced degradation. However, the most common dielectric materials that are used to passivate the n⁺ emitters of p-type cells-thermal SiO₂ and SiNX-have historically provided poor passivation of the p⁺ emitters required for n-type cells. In this paper, we demonstrate that a thin thermal-SiO₂/SiNX stack can, when appropriately fired, provide similar passivation on both p⁺ and n⁺ surfaces. Passivation studies on textured, SiO₂/SiNX passivated p⁺-Si surfaces indicate that a high-temperature firing cycle is the most important step to achieving high-quality passivation and that the positive charge in the dielectric stack may have little detrimental effect on industrial-type, high surface concentration emitters. In addition, the suitability of spin-on boric acid sources for forming uniform, well-passivated p⁺ emitters on textured surfaces was studied. This passivation scheme and spin-on boron source were used to achieve 4-cm² screen-printed n-type cells with efficiencies over 20% and open-circuit voltages up to 650 mV.