Incorporation of Clathrochelate-Based Metalloligands in Metal-Organic Frameworks by Solvent-Assisted Ligand Exchange

Iron(II) cage complexes with terminal 4-pyridyl groups can be incorporated in metal-organic frameworks (MOFs) via solvent-assisted ligand exchange (SALE). Paddle -wheeled MOFs with N,N'-di-4-pyridylnaphthalenete-tracarboxydiimide pillars were used as starting materials. Pillar exchange was nearly quantitative, despite the fact that the cage complexes are long (similar to 15 angstrom) and sterically demanding. The reactions provide products of high crystallinity, and the structures of daughter MOFs were determined by single crystal X-ray diffraction. The crystallographic analyses showed that some of the SALE experiments led to topological changes of the MOF structures

Nuclear Magnetic Resonance Study of Atomic Motion in Bimetallic Perovskite-Type Borohydrides ACa(BH₄)₃ (A = K, Rb, or Cs)

To study the dynamical properties of the novel series of bimetallic perovskite-type borohydrides ACa(BH4)3 (A = K, Rb, or Cs), we have measured the 1H and 11B nuclear magnetic resonance spectra and spin–lattice relaxation rates in these compounds over broad temperature ranges (5–560 K) and resonance frequency ranges (14–90 MHz). Our measurements have revealed several jump processes with different characteristic rates. For all the compounds studied, the spin–lattice relaxation rates at low temperatures (T < 340 K) are governed by fast reorientations of BH4 groups. However, the experimental data in this range cannot be described in terms of a single reorientational process; this suggests a coexistence of at least two types of BH4 reorientations. Taking into account the linear coordination of each BH4 group in ACa(BH4)3 by two Ca atoms, we can attribute different reorientational processes to BH4 rotations around inequivalent symmetry axes. The parameters of reorientational motion in ACa(BH4)3 have been evaluated using the model with a two-peak distribution of activation energies. It has been found that the transitions from the low-temperature phases to the high-temperature phases of ACa(BH4)3 are accompanied by the onset of translational diffusion of intact BH4 groups. However, the jump rates for these diffusive processes remain below 108 s–1 up to the high-T limits of our experimental ranges

Dynamical evolution of the 2D/3D interface: a hidden driver behind perovskite solar cell instability

Engineering two-/three-dimensional (2D/3D) perovskite solar cells is nowadays a popular strategy for efficient and stable devices. However, the exact function of the 2D/3D interface in controlling the long-term device behavior is still obscure. Here, we reveal a dynamical structural mutation of the 2D/3D interface: the small cations in the 3D cage move towards the 2D layer, which acts as an ion scavenger. If structurally stable, the 2D layer physically blocks the ion movement at the interface boosting the device stability. Otherwise, the 2D layer embeds them, dynamically self-transforming into a quasi-2D structure. The judicious choice of the 2D constituent is decisive in controlling the 2D/3D kinetics and improving the device lifetime, opening a new avenue for perovskite interface design

Doped but Stable: Spirobisacridine Hole Transporting Materials for Hysteresis-Free and Stable Perovskite Solar Cells

Four spirobisacridine (SBA) hole-transporting materials were synthesized and employed in perovskite solar cells (PSCs). The molecules bear electronically inert alkyl chains of different length and bulkiness, attached to in-plane N atoms of nearly orthogonal spiro-connected acridines. Di-p-methoxyphenylamine (DMPA) substituents tailored to the central SBA-platform define electronic properties of the materials mimicking the structure of the benchmark 2,2',7,7'-tetrakis(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-MeOTAD), while the alkyl pending groups affect molecular packing in thin films and affect the long-term performance of PSCs. Devices with SBA-based hole transporting layers (HTL) attain efficiencies on par with spiro-MeOTAD. More importantly, solar cells with the new HTMs are hysteresis-free and demonstrate good operational stability, despite being doped as spiro-MeOTAD. The best performing MeSBA-DMPA retained 88% of the initial efficiency after a 1000 h aging test under constant illumination. The results clearly demonstrate that SBA-based compounds are potent candidates for a design of new HTMs for PSCs with improved longevity

Molecular Design and Operational Stability: Toward Stable 3D/2D Perovskite Interlayers

Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next-generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI)(2)PbI(4)used as a capping layer aligns in in-plane crystal orientation, inducing a reproducible increase of approximate to 60 mV in theV(oc), a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium­(III) bis­(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV–vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described. The preferred orientation of transition dipoles in emitter/host thin films indicated more preferred orientation than homoleptic complex Ir­(ppy)₃

CCDC 1583689: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures