Vertically Aligned 2D/3D Pb–Sn Perovskites with Enhanced Charge Extraction and Suppressed Phase Segregation for Efficient Printable Solar Cells

The concept of mixed 2D/3D heterostructures has emerged as an effective method for improving the stability of lead halide perovskite solar cells, which has been, however, rarely reported in lead–tin (Pb–Sn) mixed perovskite devices. Here, we report a scalable process for depositing mixed 2D/3D Pb–Sn perovskite solar cells that deliver remarkably enhanced efficiency and stability compared to their 3D counterparts. The incorporation of a small amount (3.75%) of an organic cation 2-(4-fluorophenyl)ethylammonium iodide induces the growth of highly oriented Pb–Sn perovskite crystals perpendicularly aligned with the substrate. Moreover, for the first time, phase segregation is observed in pristine 3D Pb–Sn perovskites, which is suppressed due to the presence of the 2D perovskites. Accordingly, a high current density of 28.42 mA cm–2 is obtained due to the markedly enhanced spectral response and charge extraction. Eventually, mixed 2D/3D Pb–Sn perovskite devices with a band gap of 1.33 eV yield efficiencies as high as 17.51% and in parallel exhibit good stability.