Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative Al_yTiO_x/TiO_x Electron-Selective Contact Stack

Passivating contacts based on transition metal oxides (TMOs) have the potential to overcome existing performance limitations in high-efficiency crystalline silicon (c-Si) solar cells, which is a significant driver for continuing cost/Watt reductions of photovoltaic electricity. Herein, innovative stacks of Al-alloyed TiO_x (Al_yTiO_x) and pure TiO_x as transparent electron-selective passivating contacts for n-type c-Si surfaces are explored. An optimized stack of 2 nm Al_yTiO_x and 2 nm TiO_x is shown to provide both record-quality surface passivation and excellent electrical contact, with a surface recombination current density prefactor J ₀ of 2.4 fA cm⁻² and a specific contact resistivity ρ _c of 15.2 mΩ cm². The performance of this innovative stack significantly exceeds previously reported values for pure or doped TiO_x single layers, SiO_x/TiO_x stacks, a-Si:H/TiO_x stacks, and other transparent contact technologies. Furthermore, an excellent efficiency of 21.9% is attained by incorporating the optimized stack as a full-area rear contact in an n-type c-Si solar cell. The findings set a new benchmark for the passivation performance of metal oxide-based passivating contacts, bringing it to a level on par with state-of-the-art SiO_x/poly-Si contacts while greatly improving optical transparency.