Fabrication of P+-N-N+ silicon solar cells by simultaneous diffusion of boron and phosphorus into silicon through silicon dioxide

Abstract

A process of fabrication of P⁺‐N‐N⁺ silicon solar cells by simultaneous diffusion of boron and phosphorus into N‐type silicon through a thermally grown silicon dioxide layer ∼0.1 μm thick is described. The inherent problems of cross doping and usefulness of silicon dioxide in minimizing them are briefly discussed. The process is well suited for large‐scale production of P⁺‐N‐N⁺ back surface field silicon solar cells. With this process, the cells fabricated from single‐crystalline silicon wafers of 100 Ω cm resistivity have shown open‐circuit voltages ∼0.6 V at 28 °C under 100 mW/cm² (AM1) intensity, and the cells fabricated from polycrystalline silicon wafers of 1–2 mm in grain size and 7–27 Ω cm resistivity have shown conversion efficiencies between 10.4 and 11.4% (AM1) at 28 °C.