Understanding SiOx Layer Breakup in poly-Si/SiOx Passivating Contacts for Si Solar Cells Using Precisely Engineered Surface Textures

The contact resistivity of polycrystalline silicon on silicon oxide (poly-Si/SiO_x) passivating contacts depends on the formation of pinholes in SiO_x for thicknesses >/~1.7 nm. We fabricated these contacts on inverted pyramids and v-grooves in addition to the alkaline-textured random pyramids and planar surface morphologies. The thermal breakup of SiO_x was achieved at peak annealing temperatures of 1050 and 1100 degrees C. SiO_x breakup at 1050 degrees C resulted in pinholes created preferentially at vertices in the inverted pyramids, while at 1100 degrees C, their formation was random. The density of pinholes was greater in textured samples than in polished samples. Both chemical etching and electron beam-induced current (EBIC) were used to visualize the pinholes, the latter being sensitive only to transport pinholes in the p-n junction but not the n⁺-n junction. We ascribe this difference in EBIC images based on the contact polarity to differences in the collection probability of the minority carriers generated by the electron beam. Our work demonstrates that texture morphology can be exploited to enable the precise engineering of pinholes in poly-Si/SiO_x passivating contacts.