Remarkable long-term stability of nanoconfined metal-halide perovskite crystals against degradation and polymorph transitions

Metal-halide perovskites are promising candidates to advance optoelectronic devices but are known to suffer from rapid material degradation. Here we demonstrate that nanoconfinement is an effective strategy for the long-term stabilization of metal-halide perovskite MAPbI₃ crystals against humidity-induced degradation and temperature-induced polymorph transitions. Two-dimensional X-ray diffraction patterns of MAPbI₃ films reveal an unprecedented air-stability of up to 594 days in non-chemically modified, non-passivated MAPbI₃ films deposited on substrates imposing complete 2D confinement on the tens of nanometers length scale. Temperature-dependent X-ray diffraction analysis and optical spectroscopy further reveal the suppression of temperature-dependent phase transitions in nanoconfined MAPbI₃ crystals. Most notably, the high-temperature cubic phase of MAPbI₃, typically stable at temperatures above 327 K, remains present until a temperature of 170 K when the perovskite crystals are nanoconfined within the 100 nm diameter pores of anodized aluminum oxide templates. Photoluminescence mapping confirms that nanoconfined MAPbI₃ crystals exhibit spatial uniformity on the tens of microns length scale, suggesting that nanoconfinement is an effective strategy for the formation of high-quality, stable MAPbI₃ crystals across large areas.