Efficient Passivation and Low Resistivity for p⁺-Si/TiO₂Contact by Atomic Layer Deposition

The monolithic, two-terminal (2-T) perovskite/silicon tandem solar cell is a promising candidate to increase the power conversion efficiency beyond the theoretical limit of 29.4% for crystalline silicon solar cells. To achieve a high-efficiency 2-T tandem, it is critical to have an interface that can connect the bottom and top subcells together so that both efficient passivation and good electrical contact are achieved. The majority of works done to date in this area, applied an intermediate layer as the recombination layer between perovskite and silicon, which incurs higher manufacturing costs and an additional processing step. Here we demonstrate a unique and straightforward interlayer-free approach to passivating highly boron-doped low-resistivity n-Si using a thin layer of TiO2 fabricated by atomic layer deposition (ALD) and a suitable pretreatment of the silicon surface. The passivation of this film is found to be superior to that of thermally grown SiO2 formed at high temperatures over 700 °C. The TiOX layer leads to a sufficiently low contact resistance of 0.45 ω·cm2 and high-quality passivation with a recombination current density (J0) of 152 fA/cm2. The structure is applicable to both perovskite/Si tandems and single-junction Si solar cells.