Reduced Interface‐Mediated Recombination for High Open‐Circuit Voltages in CH3NH3PbI3 Solar Cells

Perovskite solar cells with all‐organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high‐temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron‐transporting layer of inverted perovskite cells affects the open‐circuit voltage (V_OC). It is shown that nonradiative recombination mediated by the electron‐transporting layer is the limiting factor for the V_OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH₃NH₃PbI₃ perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V_OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge‐blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V_OC and efficiency.     

Dipolar‐Distribution Cavity γ‐Fe2O3@C@α‐MnO2 Nanospindle with Broadened Microwave Absorption Bandwidth by Chemically Etching

Developing microwave absorption materials with ultrawide bandwidth and low density still remains a challenge, which restricts their actual application in electromagnetic signal anticontamination and defense stealth technology. Here a series of olive‐like γ‐Fe₂O₃@C core–shell spindles with different shell thickness and γ‐Fe₂O₃@C@α‐MnO₂ spindles with different volumes of dipolar‐distribution cavities were successfully prepared. Both series of absorbers exhibit excellent absorption properties. The γ‐Fe₂O₃@C@α‐MnO₂ spindle with controllable cavity volume exhibits an effective absorption (2O₃@C spindle reaches as high as ?45 dB because of the optimized electromagnetic impedance balance between polymer shell and γ‐Fe₂O₃ core. Intrinsic ferromagnetism of the anisotropy spindle is confirmed by electron holography. Strong coupling of magnetic flux stray lines between spindles is directly imaged. This unique morphology and facile etching technique might facilitate the study of core–shell type microwave absorbers.     

Chemische Zusammensetzung und Mikrostruktur polymerabgeleiteter Gläser und Keramiken im System Si–C–O. Teil 1: Phasenidentifikation mittels Si‐L2,3‐Ionisationskanten‐Elektronenenergieverlustspektroskopie nach dem Fingerprint‐Verfahren und energiegefilterter Durchstrahlungselektronenmikroskopie

Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 1: Phase identification by means of Si‐L_2,3‐ionisation edge electron energy‐loss spectroscopy according to the fingerprinting technique and energy‐filtered transmission electron microscopy Polymer or precursor ceramics represent a novel class of high‐performance materials that are produced by controlled pyrolysis of organometal compounds. Shrinkage and porosity resulting from thermal decomposition can be compensated by adding chemically reactive filler powders. This technique permits manufacturing of dense ceramic bulk components true to size by cost‐effective near‐net‐shape forming of cross‐linked green compacts. For process control, definition of the course of the reaction of the active fillers and thus the exact knowledge of the chemical composition and the microstructure development of the solid residues during pyrolysis of the polymer precursor is required. Due to both the great technical importance of the final ceramic products and their economical availability, in the present work, thermal decomposition of a silicone resin (polymethylsiloxane) at temperatures between 525 and 1550 °C was characterized nanochemically and microstructurally. In part 1, the results of the quantitative phase identification by means of analytical electron microscopy are reported. The bonding state of silicon was determined by fine structure analysis (Si‐L_2,3‐ionisation edge) of the electron energy‐loss spectrum and has proved to be always mainly oxidic. By means of energy‐filtered transmission electron microscopy, elemental distributions in the nanometre range were recorded. The phase separation of the polymer‐derived Si–C–O matrix into SiO₂, C and SiC could be proved definitely. The characterization of structure formation by high‐resolution imaging and diffraction methods follows in part 2.