Organic–Inorganic Perovskite Light‐Emitting Electrochemical Cells with a Large Capacitance

While perovskite light‐emitting diodes typically made with high work function anodes and low work function cathodes have recently gained intense interests. Perovskite light‐emitting devices with two high work function electrodes with interesting features are demonstrated here. Firstly, electroluminescence can be easily obtained from both forward and reverse biases. Secondly, the results of impedance spectroscopy indicate that the ionic conductivity in the iodide perovskite (CH₃NH₃PbI₃) is large with a value of ≈10^?8 S cm^?1. Thirdly, the shift of the emission spectrum in the mixed halide perovskite (CH₃NH₃PbI_3?xBr_x) light‐emitting devices indicates that I^? ions are mobile in the perovskites. Fourthly, this work shows that the accumulated ions at the interfaces result in a large capacitance (≈100 μF cm^?2). The above results conclusively prove that the organic–inorganic halide perovskites are solid electrolytes with mixed ionic and electronic conductivity and the light‐emitting device is a light‐emitting electrochemical cell. The work also suggests that the organic–inorganic halide perovskites are potential energy‐storage materials, which may be applicable in the field of solid‐state supercapacitors and batteries.     

Inorganic and Hybrid Organo‐Metal Perovskite Nanostructures: Synthesis,Properties, and Applications

Hybrid perovskite and all‐inorganic perovskite have attracted much attention in recent years owing to their successful use in the photovoltaic field. Usually the perovskite is used in its bulk form, although recently, perovskites' nanocrystalline form has received increased attention. Recent developments in the evolving research field of nanomaterial‐based perovskite are reviewed. Both hybrid organic‐inorganic and all‐inorganic perovskite nanostructures are discussed, as well as approaches to tune the optical properties by controlling the size and shape of perovskite nanostructures. In addition, chemical modifications can change the perovskite nanostructures' band‐gap, similar to their bulk counterpart. Several applications, including light‐emitting diodes, lasers, and detectors, demonstrate the latent potential of perovskite nanostructures.     

Interplay between the hot phonon effect and intervalley scattering on the cooling rate of hot carriers in GaAs and InP

The influence of hot phonon effect and intervalley scattering on the hot carrier cooling rate was investigated using femtosecond time‐resolved photoluminescence spectroscopy in bulk GaAs and InP, two electronically similar but vibrationally distinct semiconductors. In both materials, a broad photoluminescence signal that extends from the band gap energy to values larger than the pump pulse energy was observed during the first few picoseconds after photoexcitation, for different excitation energies (1.7, 1.88, and 2.4 eV) at high carrier densities (>10¹⁹ cm⁻³). Different hot carrier relaxation times were observed in GaAs and InP for different excitation energies, demonstrating the influence of intervalley scattering phenomena in GaAs. When electrons were not energetic enough to access satellite valleys, longer decay transients were observed for InP compared with GaAs. This provides experimental evidence of the hot phonon effect in InP. Temperature transients were calculated by analyzing the topography of the two‐dimensional spectra. Copyright © 2011 John Wiley & Sons, Ltd.     

Aerosol‐Synthesis of Mesoporous Organosilica Nanoparticles with Highly Reactive,Superacidic Surfaces Comprising Sulfonic Acid Entities

Combining high internal surface area with tailor‐made surface properties is pivotal for granting advanced functional properties in many areas like heterogeneous catalysis, electrode materials, membranes, or also biomimetics. In this respect, organic‐inorganic hybrid nanostructures and in particular mesoporous organosilica materials are ideal systems. Here, the preparation of mesoporous solids via a new sol–gel building block comprising sulfonic acid (R‐SO₃H) is described. The degree of organic modification is not only maximal (100%), it is also proven that the novel material exhibits superacid properties. Furthermore, an aerosol assisted method is applied for generating this material in the form of mesoporous, spherical nanoparticles with substantial colloidal stability. Highly acidic, high surface area materials, like prepared here, are promising candidates for numerous future applications like in heterogeneous catalysis or for proton conducting membranes. However, first experiments addressing the antibacterial effect of the sulfonic‐acid, mesoporous organosilica materials are shown. It is demonstrated that the superacid character is required for exhibiting sufficient antifouling activity.     

Nanostructuring of Azomolecules in Silica Artificial Opals for Enhanced Photoalignment

Many modern systems are based on photoresponsive materials, in which properties such as the refractive index need to be effectively controlled. An extensively used means of achieving this is to photoinduce birefringence by alignment of anisotropic azochromophores via light‐induced isomerization. However, the refractive index changes are typically small (<10^?2), slow (seconds or minutes) and not spontaneously reversible, which excludes use of this approach in a variety of optical systems. The drawbacks are generally attributed to hindered photoalignment due to the molecular environment, which suggests that optimizing the arrangement of the functional moieties to minimize the mobility restrictions could decisively improve the photoresponse. Here, a simple solution‐processing approach is reported for favorable distribution at the molecular level of neat azochromophore into a three‐dimensionally nanostructured hybrid system exhibiting an extremely enhanced photoresponse. The standard azoderivative Disperse Red 1 is adsorbed on silica colloidal crystals that are chosen as 3D‐templates because their photonic bandgap, which is sensitive to refractive index changes, provides a direct tool to study photostimulated processes in the chromophore. The system is thoroughly investigated with different techniques to identify molecular out‐of‐plane photoalignment as the main phenomenon responsible for the optical response, and to discern the key factors leading to improved performance. It is found that the dye molecules are spontaneously adsorbed on the silica spheres, building a highly photoreactive surface multilayer. A low amount of azochromophore allows for outstanding material response upon cw‐irradiation, as a result of very large and fast refractive index changes in the chromophore ensemble (up to 0.36 – birefringence of 1.1 – in 15 ms at 0.09 J cm^?2) that, in addition, is fully reversible by thermalization. Finally, as proof‐of‐principle for real applications, long‐duty cycle photoswitching at 100 Hz (for over 2 million cycles) is demonstrated in this system.     

Charge‐Separation Dynamics in Inorganic–Organic Ternary Blends for Efficient Infrared Photodiodes

Knowledge about the working mechanism of the PbS:P3HT:PCBM [P3HT=poly(3‐hexylthiophene), PCBM=[6,6]‐phenyl‐C₆₁ ‐butyric acid methyl ester] hybrid blend used for efficient near‐infrared photodiodes is obtained from time‐resolved photoluminescence (PL) studies. To understand the role of each component in the heterojunction, the PL dynamics of the ternary (PbS:P3HT:PCBM) blend and the binary (PbS:P3HT, PbS:PCBM and P3HT:PCBM) blends are compared with the PL of the pristine PbS nanocrystals (NCs) and P3HT. In the ternary blend the efficiency of the charge transfer is significantly enhanced compared to the one of PbS:P3HT and PbS:PCBM blends, indicating that both hole and electron transfer from excited NCs to the polymer and fullerene occur. The hole transfer towards the P3HT determines the equilibration of their population in the NCs after the electron transfer towards PCBM, allowing their re‐excitation and new charge transfer process.     

EXAFS as Powerful Analytical Tool for the Investigation of Organic–Inorganic Hybrid Materials

The potential and application of X‐ray absorption spectroscopy (XAS) for structural investigations of organic–inorganic hybrid materials, with a special emphasis on systems consisting of inorganic building blocks (clusters) embedded into polymer backbones, is extensively reviewed. In the first part of the paper, the main features of organic–inorganic hybrid materials, their classification, the synthetic approaches for their preparation, and their applications are concisely presented, whereas the particular issues related to their characterization are discussed in more detail. In the second section of the paper, the principles and the theoretical background of the XAS method, including experimental design, data reduction, evaluation, analysis, and interpretation are described and discussed. Examples of potentialities of the method for the short‐range structural investigation of inorganic nanostructures in hybrids are provided, and the state‐of‐the‐art in the field of hybrid materials is reviewed. In the third part, six different case studies belonging to our past and present experience in this field are presented and discussed, with a particular focus on their XAS investigation.