Nanomechanical signatures of degradation-free influence of water on halide perovskite mechanics

International audienceAbstract Humidity is often reported to compromise the stability of lead halide perovskites or of devices based on them. Here we measure the humidity dependence of the elastic modulus and hardness for two series of lead halide perovskite single crystals, varying either by cation or by anion type. The results reveal a dependence on bond length between, hydrogen bonding with, and polarizability/polarization of these ions. The results show an intriguing inverse relation between modulus and hardness, in contrast to their positive correlation for most other materials. This anomaly persists and is strengthened by the effect of humidity. This, and our overall findings are ascribed to the materials’ unique atomic-scale structure and properties, viz nano-polar domains and strong dynamic disorder, yet high-quality average order. Our conclusions are based on comparing results obtained from several different nano-indentation techniques, which separate surface from bulk elastic modulus, and probe different manifestations of the hardness

Nanomechanical signatures of degradation-free influence of water on halide perovskite mechanics

International audienceAbstract Humidity is often reported to compromise the stability of lead halide perovskites or of devices based on them. Here we measure the humidity dependence of the elastic modulus and hardness for two series of lead halide perovskite single crystals, varying either by cation or by anion type. The results reveal a dependence on bond length between, hydrogen bonding with, and polarizability/polarization of these ions. The results show an intriguing inverse relation between modulus and hardness, in contrast to their positive correlation for most other materials. This anomaly persists and is strengthened by the effect of humidity. This, and our overall findings are ascribed to the materials’ unique atomic-scale structure and properties, viz nano-polar domains and strong dynamic disorder, yet high-quality average order. Our conclusions are based on comparing results obtained from several different nano-indentation techniques, which separate surface from bulk elastic modulus, and probe different manifestations of the hardness

The Saga of Water and Halide Perovskites: Evidence of Water in Methylammonium Lead Tri‐Iodide

International audienceThe environment humidity effects on performance of halide perovskites (HaPs), especially MAPbI 3 , are known. Nevertheless, it is hard to find direct experimental evidence of H 2 O in the bulk materials at the levels lower than that of Monohydrate (MAPbI 3 .H 2 O). Here, for the first time, direct experimental evidence of water being released from bulk (µm-s deep) of MAPbI 3 single crystal is reported. The thermogravimetric analysis coupled with mass spectrometry (TGA-MS) of evolved gases is used to detect the MS signal of H 2 O from the penetrable depth and correlate it with the TGA mass loss due to H 2 O leaving the material. These measurements yield an estimate of the average H 2 O content of 1 H 2 O molecule per three MAPbI 3 formula units (MAPbI 3 .0.33H 2 O). Under the relatively low temperature conditions no other evolved gases that can correspond to MAPbI 3 decomposition products, are observed in the MS. In addition to being direct evidence that there is H 2 O inside MAPbI 3 , the data show that H 2 O diffuses into it. With this article, a solid basis is proved for further studies on the mechanisms through which water modifies the properties of MAPbI 3 and all the other halide perovskites

Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals

We show that formamidinium-based crystals are distinct from methylammonium-based halide perovskite crystals because their inorganic sublattice exhibits intrinsic local static disorder that coexists with a well-defined average crystal structure. Our study combines terahertz-range Raman scattering with single-crystal X-ray diffraction and first-principles calculations to probe the evolution of inorganic sublattice dynamics with temperature in the range of 10–300 K. The temperature evolution of the Raman spectra shows that low-temperature, local static disorder strongly affects the crystal structural dynamics and phase transitions at higher temperatures

Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals

We show that formamidinium-based crystals are distinct from methylammonium-based halide perovskite crystals because their inorganic sublattice exhibits intrinsic local static disorder that coexists with a well-defined average crystal structure. Our study combines terahertz-range Raman scattering with single-crystal X-ray diffraction and first-principles calculations to probe the evolution of inorganic sublattice dynamics with temperature in the range of 10–300 K. The temperature evolution of the Raman spectra shows that low-temperature, local static disorder strongly affects the crystal structural dynamics and phase transitions at higher temperatures

Static and Dynamic Disorder in Formamidinium Lead Bromide Single Crystals

We show that formamidinium-based crystals are distinct from methylammonium-based halide perovskite crystals because their inorganic sublattice exhibits intrinsic local static disorder that coexists with a well-defined average crystal structure. Our study combines terahertz-range Raman scattering with single-crystal X-ray diffraction and first-principles calculations to probe the evolution of inorganic sublattice dynamics with temperature in the range of 10–300 K. The temperature evolution of the Raman spectra shows that low-temperature, local static disorder strongly affects the crystal structural dynamics and phase transitions at higher temperatures