Characterizing Inkjet-Printed Localized n+ and p+ Poly-Si Passivating Contacts for Silicon Solar Cells: Comparisons and Insights

Herein, we fabricate and characterize localized boron- and phosphorus-doped polycrystalline silicon (poly-Si)/SiO_x passivating contacts for silicon solar cells by maskless inkjet printing technology with commercially sourced liquid dopant inks. Moreover, we leverage the advantages of inkjet printing to demonstrate the simultaneous formation of localized p+ and n+ poly-Si/SiO_x passivating contact lines by a single anneal at 950 °C for 60 min. Optical microscopy images reveal well-defined dopant lines with features down to ∼60 μm. Microphotoluminescence (μPL) mapping confirms the enhanced surface passivation in the locally printed regions compared to the unprinted regions due to doping. In addition, high-resolution dynamic secondary ion mass spectrometry (SIMS) measurements quantify the total dopant concentrations in the lines, and electrochemical capacitance-voltage (ECV) was applied to measure the electrically active dopant concentrations in co-processed pads. The μPL and SIMS maps clearly reflect the line shapes from optical microscopy images, and exhibit sharp line features, irrespective of line widths or dopant species. More importantly, SIMS analysis highlights unintended doping in unprinted regions and cross-doping when both polarities are co-annealed. Introducing a thick spin-on SiO_x protective layer in unprinted regions effectively mitigates unintended doping. Comparison of the μPL and SIMS maps suggests that the unintended doping arises from volatile dopant species released into the gas phase, rather than from the lateral diffusion of dopants. The benefits and limitations of the characterization methods are also discussed. These findings provide valuable insights for the further optimization of inkjet printing for localized doping of poly-Si/SiO_x passivating contacts, particularly in interdigitated back contact solar cell architectures.