Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28%

Abstract Atomic layer deposition (ALD) growth of conformal thin SnO x films on perovskite absorbers offers a promising method to improve carrier‐selective contacts, enable sputter processing, and prevent humidity ingress toward high‐performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD‐SnO x film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnO x can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnO x buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnO x structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0 cm 2 ) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.