Stabilizing Metal-Halide Perovskites via Nanoconfined Crystallization*

Metal-halide perovskites undergo multiple polymorph transitions, with the smallest bandgap phases thermodynamically favored at elevated temperatures. We explore nanoconfinement as a strategy to shift the thermodynamics of polymorph transitions in order to stabilize high-performance phases against temperature-induced polymorph transitions and humidity-induced degradation.¹ Specifically, when crystal sizes are reduced, the surface free energy contribution to the total Gibbs free energy of the crystals becomes increasingly important. By exploiting the dependence of the surface free energy on the symmetry of the crystal structure, it is possible to shift polymorph transitions to lower temperatures under nanoconfinement compared to the bulk.^2,3 These nanoconfined crystals also exhibit excellent stability against humidity-induced degradation, with no change in their X-ray diffraction patterns over a period of at least two years of storage in air.

¹X. Kong, K. Zong, S.S. Lee. Chem. Mater., 31, 4953 (2019).
²X. Kong, K. Shayan, S. Lee, C. Ribeiro, S. Strauf, S.S. Lee. Nanoscale, 10, 8320 (2018).
³X. Kong, K. Shayan, S. Hua, S. Strauf, S.S. Lee. ACS Appl. Energy Mater., 2, 2948 (2019).