(604c) A Thermodynamic Basis for Engineering Enhanced Stability of the Perovskite Phase of Cesium Lead Iodide

The perovskite phase of cesium lead iodide (α-CsPbI₃ or “black” phase), possesses excellent absorptivity, charge carrier mobility and recombination kinetics for photovoltaic applications. However, the stable phase at room temperature is a non-functional, “yellow” phase (δ-CsPbI₃). Using differential scanning calorimetry, it is shown herein that the desired black phase can be captured in a metastable state that is maintained in the absence of moisture, up to a temperature of 100°C. A reversible phase-change enthalpy of 14.2 (± 0.5) kJ/mol is measured, implying a large entropic stabilization of the black phase. In order to engineer enhanced stability of the perovskite phase, particularly toward atmospheric moisture, this entropic contribution to the stability is intentionally maximized through nanostructuring of the thin film. These results enhance the utility of this promising photovoltaic material and contribute more generally to our fundamental understanding of the effects of common processing steps on the larger family of lead-halide perovskites.