Halide perovskites have attracted tremendous interest due to their promise as a solution-processable active layer in solar cells with efficiencies rivaling commercial silicon solar cells. The highest efficiency halide perovskite solar cells incorporate methylammonium lead iodide (CH3NH3PbI3), which tends to decompose under normal operating conditions. One approach to stabilizing halide perovskite solar cells is to replace the organic cation with an inorganic Cs+ cation. While cesium lead iodide (CsPbI3) has a much higher decomposition temperature than CH3NH3PbI3, introducing Cs+ is problematic because the size of the Cs+ cation is near the lower limit for lead iodide perovskite formation. Accordingly, CsPbI3 is only thermodynamically stable as a perovskite above ~325 °C, where it is cubic (α-CsPbI3), and at ambient conditions it rapidly converts to a yellow material consisting of one-dimensional chains of Pb-I octahedra (δ-CsPbI3). We use a solid-state method to synthesize single crystals of perovskite-phase cesium lead iodide (γ-CsPbI3) that are kinetically stable at room temperature. Single crystal X-ray diffraction characterization shows the compound is orthorhombic with the GdFeO3 structure at room temperature. Unlike conventional semiconductors, the optical absorption and joint density-of-states of bulk γ-CsPbI3 is greatest near the band edge and decreases beyond Eg for at least 1.9 eV. Bulk γ-CsPbI3 does not show an excitonic resonance and has a smaller optical band gap than has been reported in thin films; these and other differences indicate that previously-measured thin film γ-CsPbI3 shows signatures of quantum confinement. By flowing gases in situ during powder X-ray diffraction measurements, we confirm that γ-CsPbI3 is stable to oxygen but rapidly and catalytically converts to non-perovskite δ-CsPbI3 in the presence of moisture. Our results provide vital parameters for theoretical and experimental investigations into perovskite-phase CsPbI3 that will the guide the design and synthesis of atmospherically stable inorganic halide perovskites.

Kinetically stable single crystals of perovskite-phase CsPbI3

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.