(508e) Effects of 3D-Interfacial Strain on the Perovskite Phase Stability of CsPbI3 in Silica Inverse Opal Scaffolds

The strain between any two interfaces in a functional composite material is inevitable, and has in limited cases been intentionally engineered to improve superconductivity, ferromagnetism, and phase stability. Herein, we explore whether such interfacial strain can stabilize the symmetric, low density, cubic perovskite phase of CsPbI₃, which is a promising absorber material for photovoltaic devices. We hypothesized that if a soft material like CsPbI₃ is synthesized within a rigid metal oxide scaffold at high temperature and then rapidly quenched, a tensile interfacial stress will be generated due to the mismatch in the thermal expansion coefficients of CsPbI₃ and the metal oxide. Substrate-clamped CsPbI₃ has been previously hypothesized to retain its perovskite phase at room temperature due to the necessary tensile strain generated at the heterointerface, yet only metastability has been observed till date. However, such substrate induced strain is usually biaxial and results in a non-uniform strain distribution in the crystal lattice. In this work, we crystallized CsPbI₃ in the perovskite phase inside silica inverse opals at elevated temperatures and quenched them. We evaluate how three-dimensional (i.e., isotropic) tensile strain generated by this thermally induced stress differs from its bi-axial counterpart, and what role the resulting perovskite lattice strain plays in room temperature crystal phase thermodynamics. We used X-ray diffraction to identify the phase and estimate lattice expansion as a function of thermal excursions imposed on the CsPbI₃-scaffold composite.