Tuning the Energetic Landscape of Ruddlesden–Popper Perovskite Films for Efficient Solar Cells

Ruddlesden–Popper perovskite films deposited with different methods show very diverse phase segregation and composition. When DMSO is used as solvent, the conventional method based on spin-coating and annealing produces very poor devices, whereas the vacuum-assisted method proposed here allows obtaining devices with efficiency up to 14.14%. The conventional method gives rise to a three-dimensional (3D)-like phase on the top of the film but dominant n = 2 phase with large domains (∼40 μm) at the bottom of the film. These n = 2 domains are oriented with their inorganic slabs parallel to the substrate and inhibit the charge transport in the vertical direction. Consequently, severe monomolecular and bimolecular charge recombination occurs in the solar cells. Conversely, the vacuum-assisted method yields films with a 3D-like phase dominant throughout their entire thickness and only a small amount of n ≤ 2 domains of limited dimensions (∼3 μm) at the bottom, which facilitate charge transport and reduce charge recombination.