Anomalous phase transitions in one-dimensional organo-metal halide perovskite nanorods grown inside porous silicon nanotube templates

摘要

One-dimensional organo-metal halide Perovskite (CH3NH3PbI3) nanorods whosediameter and length are dictated by the inner size of porous silicon nanotubetemplates have been grown, characterized and compared to bulk perovskites inthe form of microwires. We have observed a structural phase transition for bulkperovskites, where the crystal structure changes from tetragonal toorthorhombic at about 150K, as opposed to small diameter one-dimensionalperovskite nanorods, of the order of 30-70 nm in diameter, where the phasetransition is inhibited and the dominant phase remains tetragonal. Two majorexperimental techniques, infrared absorption spectroscopy andphotoluminescence, were utilized to probe the temperature dependence of theperovskite phases over the 4-300K temperature range. Yet, differentcharacteristics of the phase transition were measured by the two spectroscopicmethods and explained by the presence of small, tetragonal inclusions embeddedin the orthorhombic phase. The inhibition of the phase transition is attributedto the large surface area of these one-dimensional perovskite nanorods, whichgives rise to a large stress that, in turn, prevents the formation of theorthorhombic phase. The absence of phase transition enables the measurement ofthe tetragonal bandgap energy down to low temperatures.