Improved emitter performance of RIE black silicon through the application of in-situ oxidation during POCl₃ diffusion

Nano-texture has the potential to reduce the optical losses of crystalline silicon solar cells. RIE fabricated black silicon enables near zero reflectance across a broad range of wavelengths and the angular dependence has been shown to be superior to existing technologies. However, in front-contact cells which are the current industrial mainstream architecture, the emitter is located on the front textured side and is typically realized by POCl₃ diffusion. The interaction of this process with the nano-texture is complex, which makes it challenging to optimise the electrical performance of the phosphorus emitter. This paper studies the impact of in-situ oxidation during emitter formation to the electrical performance of a POCl₃ diffused RIE nanotextured emitter surface. Additional corona charge was applied on the ALD SiO₂/Al₂O₃ stack to avoid the limitation on the emitter performance due to non-ideal surface passivation conditions. After saturation with surface charge, the results demonstrate in-situ oxidation to be an effective technique to improve the electrical performance. An emitter recombination factor of 147 fA/cm² was achieved for a 127 Ω/□ emitter formed on reactive-ion etched sample with surface area enhancement factor and effective slope index of 4.19 and 1.63, respectively. Further paths for improvement are identified, particularly relating to the collection of carriers generated by short wavelength light and how that relates to the shape of the texture used.