Low-cost and efficient interfacial layer construction with the required charge selectivity and compatibility is necessary for nanostructured solar cells, and the proper integration of the interfacial layer with the light-trapping system is required to improve the power conversion efficiency of the cell. Herein, low-cost Si nanowires-based solar cells with tunneling heterojunctions are developed by the deposition of MoO x and spin-coating of Cs 2 CO 3 as the carrier-selective layers. The power conversion efficiency of 16.9% for a device of 4 cm 2 in area is achieved by Si nanowires solar cells by the self-assembly of ultra-thin SiO x as the surface tunneling passivation layer. Self-assembly is realized with an ultraviolet O 3 treatment process at room temperature. Quasi-steady-state photoconductance, microwave-detected photoconductance decay, and constant current-voltage measurements are used to characterize the passivation quality and tunneling transportation properties of the ultra-thin SiO x layers. Interfacial charge recombination is suppressed and effective carrier tunneling properties are developed by the growth of ≈1.5 nm thick SiO x layers on the surfaces of the Si nanowires. This proposed Si nanowires solar cell architecture featuring tunneling heterojunctions achieves high performance and may be suitable for fabricating industrialized Si nanowires-based photovoltaic devices through a cost-effective, simple, and low-temperature process.