High-Performance TiO₂-Based Electron-Selective Contacts for Crystalline Silicon Solar Cells

A high-quality, low-cost TiO₂ -based electron-selective contact for silicon solar cells was developed. Thin TiO₂ films were deposited by ALD with the titanium chloride titanium precursor and H₂O oxidant at a low temperature of 75°C, and N₂ was used as the purge gas. To investigate the surface passivation quality of thin TiO₂ on silicon surfaces, symmetrical test structures were fabricated on (100)-oriented n-type and p-type silicon wafers to allow injection-dependent lifetime measurement utilizing the quasi-steady state Photoconductance (QSSPC) technique. The wafers were chemical-polished and RCA cleaned followed by a short dip in diluted HF before TiO₂ film deposition. TiO₂ film thicknesses were determined from ellipsometry measurement by fitting polarized reflectance data of single side polished silicon wafers. The implementation of the TiO₂ -based contacts reduces the surface recombination and contact resistivity at the silicon and metal interface simultaneously, resulting in a higher V oc and FF for silicon solar cells. The champion efficiency of 21.6% has been achieved on the n-type silicon solar cell featuring a full-area TiO₂ -based contact.