The application of high pressure allows tuning physicochemical properties of materials by changing interatomic distances. Pressure may also induce structural phase transitions into new phases with enhanced or novel functional properties. Here, we report complementary high-pressure single-crystal X-ray diffraction, Raman spectroscopy, and optical studies of a two-dimensional (2D) perovskite, MHy 2 PbBr 4 , comprising a very small spacer cation (methylhydrazinium, MHy + ). This crystal exhibits highly desired ferroelectric and extraordinary multiple linear and nonlinear optical (NLO) properties. Single-crystal X-ray diffraction shows that MHy 2 PbBr 4 undergoes an unusual Pmn2 1 → P2 1 phase transition near 4 GPa, associated with the extrusion of some MHy + cations from the interlayer space into voids located within the inorganic sheets, not reported for any 2D hybrid perovskite. The transport of counter cations leads to a significant increase of Pb− NH 2 interactions, an unprecedented threefold increase of positive linear compressibility perpendicular to the polyanionic layers and a large negative linear compressibility of −22.39 TPa −1 within the layers. The Raman data confirm the association of the phase transition with strong distortion of the crystal structure and reorganization of the hydrogen bond network, while the absorption spectra of the compressed ambient-pressure Pmn2 1 phase show the band gap narrowing, followed by its widening in the highpressure P2 1 phase. A similar change in the pressure dependence from a red shift to a blue shift is also observed for the free-exciton (FE) photoluminescence (PL). Furthermore, the pressure-induced phase transition leads to a giant enhancement of PL intensity, especially pronounced for the broad-band emission attributed to the self-trapped excitons (STEx). We attribute the effects, observed in absorption and PL spectra, to the shortening of Pb−Br bonds in the ambient pressure phase and increased distortion of the inorganic layers and tilts of PbBr 6 octahedra in the high-pressure phase. Overall, our results for a 2D hybrid compound comprising very small spacer cations extend the understanding of the pressure effect on the properties of 2D hybrid perovskites in general and demonstrate a very different behavior under compression compared to the analogues with large organic cations. They revealed that the structure−strain mechanism can be used for engineering new high-pressure phases with unusual structural, mechanical, and optoelectronic properties.

Stealth technology combines numerous means and techniques to be 'invisible' for opponents in a battle field. Since metals are the key construction materials of military vehicles, weapon and equipment, they can be targeted and detected by RAdio Detection And Ranging (RADAR) systems. Radar-Absorbent Materials (RAMs)as crucial components of passive countermeasures in the modern-day military tacticsare used for absorption of electromagnetic waves. In the same time, mainly due to high electric conductivity, RAMsaccompanied by designed geometry of the objects they are incorporated intocan yield programmable reflection, multiple internal reflection and scattering towards Electromagnetic *Manuscript Click here to view linked References Interference (EMI) shielding. Nowadays, the latest achievements of nanotechnology have transformed stealth technology into an even more powerful tool. And among many nanomaterials, carbon nanotubes (CNTs) have arisen as one of the most promising active component of RAMs and EMI shielding materials. The unique sp 2 -derived macromolecular architecture equips CNTs with an exceptional combination of electromagnetic, mechanical and chemical properties. This review intends to summarize and critically evaluate the hitherto efforts in the production and applications of CNT nanocomposites/hybrid materials as key constructional civil and military elements, preferably as coatings, layers, films, textiles or panels, towards attenuation of the radio wave radiation.

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Mixing molecular cations in hybrid lead halide perovskites is a highly effective approach to enhance the stability and performance of optoelectronic devices based on these compounds. In this work, we prepare and study novel mixed 3D methylammonium (MA)−ethylammonium (EA) MA 1−x EA x PbI 3 (x < 0.4) hybrid perovskites. We use a suite of different techniques to determine the structural phase diagram, cation dynamics, and photoluminescence properties of these compounds. Upon introduction of EA, we observe a gradual lowering of the phase-transition temperatures, indicating stabilization of the cubic phase. For mixing levels higher than 30%, we obtain a complete suppression of the low-temperature phase transition and formation of a new tetragonal phase with a different symmetry. We use broad-band dielectric spectroscopy to study the dielectric response of the mixed compounds in an extensive frequency range, which allows us to distinguish and characterize three distinct dipolar relaxation processes related to the molecular cation dynamics. We observe that mixing increases the rotation barrier of the MA cations and tunes the dielectric permittivity values. For the highest mixing levels, we observe the signatures of the dipolar glass phase formation. Our findings are supported by density functional theory calculations. Our photoluminescence measurements reveal a small change of the band gap upon mixing, indicating the suitability of these compounds for optoelectronic applications.

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Within a decade, perovskite solar cells (PSCs) leaped to the forefront of photovoltaic research, rapidly moving toward the industrial phase. Despite the impressive progress in technology development and new efficiency records, there still remains a large scope for further advancement. Utilization of scalable deposition methods and good control of the perovskite crystallization process, especially with industrially compatible fabrication protocols, require more understanding to ascertain reproducible, large-format manufacturing. Here, we report ink formulation development for ink-jet printing of perovskite thin films in ambient conditions. We used the precursor solution on a nonhazardous solvent system, fulfilling industrial requirements. By carefully adjusting the coordination environment of the Pb2+ through additive engineering, we were able to tune the nucleation process and achieve uniform, pinhole-free perovskite thin films. Furthermore, we combined multiple characterization techniques with computational methods to analyze Pb-complex structures and evaluate their influence on perovskite formation. Lastly, we applied ink-jet printed photoactive layers into large-area (1 cm2) photovoltaic devices and processed on flexible substrates (PET foil). Inverted (p–i–n architecture) PSCs, based on multication composition, Cs0.1[(HC­(NH2)2)0.83(CH3NH3)0.17]0.9Pb­(I0.83Br0.17)3, delivered 11.4% of power conversion efficiency.

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