Chemical vapor deposition and thermal stability of two-dimensional Pb-Sn binary-metal perovskite thin films

2D-metal halide perovskites have attracted considerable attention, mainly due to its unique opto-electronic properties and exceptional stability in an ambient environment. This has significant implications for its application in solar cells with long-term operational stability. Global regulations on the use of toxic elements in industrial products requires a lead (Pb)-reduction in perovskite solar cells. Tin (Sn) is the preferred candidate as a replacement for Pb, since it meets the ionic size, coordination and charge balance requirements. The 2D perovskites can be grown by a variety of techniques, of which chemical vapor deposition (CVD) is favorable in terms of scalability and repeatability. Large cation constituents; e.g. phenethylammonium iodide (PEAI), are used to produce 2D phenethylammonium lead iodide (PEA₂PbI₄). We report on a 3-step CVD process for the deposition of a 2D Pb-Sn perovskite thin film, where the conversion temperature (from the binary-metal halide to the perovskite) is optimized at 100 °C, as confirmed by the well-defined grain boundaries and the characteristic exciton absorption and emission features. Furthermore, photoluminescence measurements from 20 – 300 K confirm the improved optical and structural stability of the single-metal films (Pb or Sn only), which is attributed to the size effect of the PEA molecule. Lastly, we will report on the electron-phonon interaction of the 2D Pb-Sn perovskite layer.