Optimization of a Solution-Processed TiO/(n)c-Si Electron-Selective Interface by Pre- and Postdeposition Treatments

Developing a vacuum-free and low-temperature deposition technique for dopant-free carrier-selective materials without sacrificing their performance can reduce the fabrication cost and CO₂ footprint of silicon heterojunction (SHJ) solar cells. In this contribution, to activate the full capacity of the solution-processed TiO as an electron-selective passivation contact, the effects of various pre- and postdeposition treatments on the passivation quality and contact resistivity are investigated simultaneously. It is demonstrated that the electrical properties of a thin TiO layer spin-coated on an n-type silicon substrate can be remarkably improved through tailor-made pre- and postdeposition treatments. A notable low surface recombination velocity (SRV) of 6.54 cm/s and a high implied open-circuit voltage (iV_oc) of 706 mV are achieved. In addition, by inserting a 1 nm LiF buffer layer between TiO and Al metal contact, a low contact resistivity (ρc) of 15.4 mΩ·cm² is extracted at the n-Si/SiO/TiO heterojunction. Our results bring the solution-processed TiO electrical properties to a level on par with those of state-of-the-art pure TiO layers deposited by other techniques. Chemical and electrical characterizations elucidate that the improved electrical properties of the investigated Si/SiO/TiO heterojunction are mediated by the concomitant involvement of chemical and field-effect passivation.