Metal-halide perovskite semiconductors are of tremendous interest for a variety of applications. Only recently, solar cells based on a representative of this family have been certified with an efficiency in excess of 24%.[1] Aside from their remarkable success in photovoltaics, metal-halide perovskites are also highly promising as light emitters, e.g., in light-emitting diodes (LEDs) or lasers. [2][3][4] LEDs based on the fruit-fly of these compounds, i.e., methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPbI 3 ), and other related perovskites have been demonstrated with continuously increasing efficiency. [5][6][7] For lasers, there is the vision that perovskites may overcome/avoid the typical limitations and loss mechanisms present in organic gain media, such as triplet-singlet annihilation or absorption due to triplet excitons and Cesium lead halide perovskites are of interest for light-emitting diodes and lasers. So far, thin-films of CsPbX 3 have typically afforded very low photoluminescence quantum yields (PL-QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX 3 nanoparticles (NPs).Here, thin films of cesium lead bromide, which show a high PL-QY of 68% and low-threshold ASE at RT, are presented. As-deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin-film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX 3 perovskites can only be achieved with NPs.

Photonic nanostructures are created in organo-metal halide perovskites by thermal nanoimprint lithography at a temperature of 100 °C. The imprinted layers are significantly smoothened compared to the initially rough, polycrystalline layers and the impact of surface defects is substantially mitigated upon imprint. As a case study, 2D photonic crystals are shown to afford lasing with ultralow lasing thresholds at room temperature.

Thermal management in devices like solar cells, light-emitting diodes, and lasers based on hybrid halide perovskite thin films is expected to be of paramount importance for optimal performance and reliability. As of yet, experimental data of thermal properties of non-iodine-based hybrid halide perovskites is very scarce. Here the thermal conductivity of methylammonium lead halide perovskite (CH3NH3PbX3 X= I, Br, and Cl) single crystals and thin films is analyzed by scanning near-field thermal microscopy. The thermal conductivity of CH3NH3PbX3 single crystals with X= I, Br, and Cl is found to be 0.34 ± 0.12, 0.44 ± 0.08, and 0.50 ± 0.05 W/(mK) at room temperature, respectively. Strikingly, similar thermal conductivities are determined for the corresponding thin-film samples. The thermal conductivity of MAPbI3 in the cubic phase (T > 55 °C) increases to (1.1 ± 0.1) W/(mK). In addition, the temperature dependence of the thermal conductivities and of thermal expansion coefficients of MAPbI3 around the phase transition from the tetragonal to cubic phase is presented.

Hybrid perovskite semiconductors hold great promise as low‐cost, yet high performance gain media for lasers. Distributed feedback (DFB) resonator structures are a key to unlock low laser threshold levels, which are essential on the way to the first electrically operated perovskite laser diode. Here, the first DFB lasers based on methylammonium lead bromide (MAPbBr3) thin films, with a linear photonic grating imprinted into the MAPbBr3 active layers is presented. High‐Q Bragg resonator gratings with a periodicity of 300 nm are directly patterned by thermal nanoimprinting into thin films of MAPbBr3 at a temperature as low as 100 °C. A notable effect of the imprinting process is a substantial flattening of the initially very rough polycrystalline perovskite layers to layers consisting of large crystals on the order of tens of microns with a surface roughness of 0.6 nm. The smooth surface affords a significantly lowered threshold for the onset of amplified spontaneous emission due to reduced scattering. In optically pumped DFB laser structures, very low lasing thresholds of 3.4 µJ cm−2 are achieved. It is foreseen that these results will influence research on perovskite‐based optoelectronic devices beyond lasers, e.g., light emitting diodes and solar cells.

Perovskites have high potential for future electronic devices, in particular, in the field of opto-electronics. However, the electronic and optic properties of these materials highly depend on the morphology and thus on the preparation; in particular, highly crystalline layers with large crystals and without pinholes are required. Here, nanoimprint is used to improve the morphology of such layers in a thermal imprint step. Two types of material are investigated, MAPbI3 and MAPbBr3, with MA being methylammonium, CH3NH3+. The perovskite layers are prepared from solution, and the crystal size of the domains is substantially increased by imprinting them at temperatures of 100–150 °C. Although imprint is performed under atmospheric conditions which, in general, enhances the degradation, the stamp that covers the layer under elevated temperature is able to protect the perovskite largely from decomposition. Comparing imprinting experiments with pure annealing at a similar temperature and time proves this. Furthermore, imprint is capable of patterning the surface of the perovskite layers; lines and spaces of 150 nm width were reproducibly obtained under imprint at 150 °C. Moreover, a through-layer patterning is possible by using the partial cavity filling approach. Although not yet optimized, this simple way to define isolated perovskite patterns within a layer simply by thermal nanoimprint is of impact for the preparation of devices, as patterning of perovskite layers by conventional techniques is limited.

A series of novel amphiphiles were synthesized based entirely on renewable resources. Besides their efficacy as supramolecular gelators in a wide variety of organic solvents and also water, their surface properties as surfactants and emulsifiers have been determined. A methodical study revealed that the length of the hydrocarbon chains has a dramatic and decisive influence on the thermal stabilities of the obtained hydrogels.

Detailed complex investigations of the spectral and physical characteristics for cubic Bi,G%0,-Nd3+ crystals were made. An analysis of absorption, luminasoence, and stimulated emission spectra for ,F3/2 + 4111/2 and 4F3/2 -r 4113/2 transitions were carried out. The luminescence lifetime of the metastable state, inter-multiplet and "Stark" luminescence branching coefficients, luminescence quantum efficiency, luminescence line width, spontaneous transition probabilities and stimulated-emission transition cross-sections were determined. The temperature dependence of the stimulated-emission (4F3/2 + 4111/2) excitation threshold was investigated and interpreted. Preliminary conclusions on the activator centre structure of Nd3+ ions in Bi,Ge,O,, were made, and informations on the extent of the vibronic spectra of Bi4Gg0,, crystals were obtained. xapaKTepmTm K Y~H~~C K O~O KptlcTanna Bi,Ge,O,,-Nd3+. IIpoBenea a~a n~3 cnew 9emH ~n 5 i ABYX nepexoAoB 4F3/2 -*I11/2 II 4F3/2 +4113/2. B pa6ol.e 6b1nl1 OnpeAeneHbI: npOBeAeHbI AeTaJIbHbIe KOMIIJIeKCHbIe HCCJIeAOBaHH5i CIIeKTpanbHO-rpH3HseCKIlX

The manufacturing of devices from methylammonium-based perovskites asks for reliable and scalable processing. As solvent engineering is not the option of choice to obtain homogeneous layers on large areas, our idea is to ‘upgrade’ a non-perfect pristine layer by recrystallization in a thermal imprint step (called ‘planar hot pressing’) and thus to reduce the demands on the layer formation itself. Recently, imprint has proven both its capability to improve the crystal size of perovskite layers and its usability for large area manufacturing. We start with methylammonium lead bromide layers obtained from a conventional solution-based process. Acetate is used as a competitive lead source; even under perfect conditions the resulting perovskite layer then will contain side-products due to layer formation besides the desired perovskite. Based on the physical properties of the materials involved we discuss the impact of the temperature on the status of the layer both during soft-bake and during thermal imprint. By using a special imprint technique called ‘hot loading’ we are able to visualize the upgrade of the layer with time, namely a growth of the grains and an accumulation of the side-products at the grain boundaries. By means of a subsequent vacuum exposition we reveal the presence of non-perovskite components with a simple inspection of the morphology of the layer; all experiments are supported by X-ray and electron diffraction measurements. Besides degradation, we discuss recrystallization and propose post-crystallization to explain the experimental results. This physical approach towards perovskite layers with large grains by post-processing is a key step towards large-area preparation of high-quality layers for device manufacturing.