On elimination of inactive phosphorus in industrial POCl3 diffused emitters for high efficiency silicon solar cells

It is compelling to eliminate inactive phosphorus in industrial POCl3 diffused emitters for high efficiency silicon solar cells. Several approaches were reported to significantly reduce inactive phosphorus in the literature. However, the underlying physical mechanisms are not fully understood. In this work, we conduct a systematic investigation and fabricate eight emitters involving two POCl3:O2 ratios at pre-deposition and both inert and oxidising scenarios at drive-in. Characterization techniques such as secondary ion mass spectrometry and X-ray photoelectron spectroscopy are carried out with an emphasis on the phosphosilicate glass. To provide a consistent interpretation of our results and those in the literature, we suggest a probable reaction, “free phosphorus oxidation”, as the dominant mechanism to unveil the role and impact of oxygen during POCl3 diffusion. We further propose that various industrial POCl3 emitters can be fabricated inactive phosphorus free without drive-in or a pre-grown oxide. Among the eight emitters, three emitters are free from inactive phosphorus with a sheet resistance range from 65 to 140 Ω/□, featuring a surface doping from 1 × 1020 to 3 × 1020 cm−3 and a remarkably low emitter saturation current density down to 51 fA/cm2.