Diego Solis-Ibarra

A Layered Hybrid Perovskite Solar‐Cell Absorber with Enhanced Moisture Stability

Two-dimensional hybrid perovskites are used as absorbers in solar cells. Our first-generation devices containing (PEA)2(MA)2[Pb3I10] (1; PEA=C6H5(CH2)2NH3(+), MA=CH3NH3(+)) show an open-circuit voltage of 1.18 V and a power conversion efficiency of 4.73%. The layered structure allows for high-quality films to be deposited through spin coating and high-temperature annealing is not required for device fabrication. The 3D perovskite (MA)[PbI3] (2) has recently been identified as a promising absorber for solar cells. However, its instability to moisture requires anhydrous processing and operating conditions. Films of 1 are more moisture resistant than films of 2 and devices containing 1 can be fabricated under ambient humidity levels. The larger bandgap of the 2D structure is also suitable as the higher bandgap absorber in a dual-absorber tandem device. Compared to 2, the layered perovskite structure may offer greater tunability at the molecular level for material optimization.

Trinuclear Pd3O2 Intermediate in Aerobic Oxidation Catalysis

The activation of O2 is a key step in selective catalytic aerobic oxidation reactions mediated by transition metals. The bridging trinuclear palladium species, [(LPd(II))3(μ(3)-O)2](2+) (L=2,9-dimethylphenanthroline), was identified during the [LPd(OAc)]2(OTf)2-catalyzed aerobic oxidation of 1,2-propanediol. Independent synthesis, structural characterization, and catalytic studies of the trinuclear compound show that it is a product of oxygen activation by reduced palladium species and is a competent intermediate in the catalytic aerobic oxidation of alcohols. The formation and catalytic activity of the trinuclear Pd3O2 species illuminates a multinuclear pathway for aerobic oxidation reactions catalyzed by Pd complexes.

A Direct Bandgap Copper–Antimony Halide Perovskite

Since the establishment of perovskite solar cells (PSCs), there has been an intense search for alternative materials to replace lead and improve their stability toward moisture and light. As single-metal perovskite structures have yielded unsatisfactory performances, an alternative is the use of double perovskites that incorporate a combination of metals. To this day, only a handful of these compounds have been synthesized, but most of them have indirect bandgaps and/or do not have bandgaps energies well-suited for photovoltaic applications. Here we report the synthesis and characterization of a unique mixed metal ⟨111⟩-oriented layered perovskite, Cs4CuSb2Cl12 (1), that incorporates Cu2+ and Sb3+ into layers that are three octahedra thick (n = 3). In addition to being made of abundant and nontoxic elements, we show that this material behaves as a semiconductor with a direct bandgap of 1.0 eV and its conductivity is 1 order of magnitude greater than that of MAPbI3 (MA = methylammonium). Furthermore, 1 has high photo- and thermal-stability and is tolerant to humidity. We conclude that 1 is a promising material for photovoltaic applications and represents a new type of layered perovskite structure that incorporates metals in 2+ and 3+ oxidation states, thus significantly widening the possible combinations of metals to replace lead in PSCs.

Facile Synthesis of Zero-, One-, and Two-Dimensional Vanadyl Pyrophosphates

Crystallization of Na(2)VOP(2)O(7) from its aqueous solution results in formation of a one-dimensional inorganic polymer {Na(2)VO(H(2)O)P(2)O(7)·7H(2)O}(n) (1). When this polymer is dehydrated at elevated temperatures this polymer undergoes a phase transition to form the two-dimensional framework β-Na(2)VOP(2)O(7), which although previously reported had been difficult to access. Exchanging lithium for sodium via ion-exchange chromatography results in formation of a discrete, cyclic, tetramer species, Li(8)[VOP(2)O(7)(H(2)O)·4H(2)O](4) (2). Isolation of crystalline β-Li(2)VOP(2)O(7) using a dehydration procedure analogous to the one employed for the sodium derivative was unsuccessful. In contrast, we show that β-K(2)VOP(2)O(7) can be obtained from the amorphous phase K(2)VOP(2)O(7)·nH(2)O (n = 0-7) upon thermal dehydration.

Molecular gallosilicates and their group 4 multimetallic derivatives.

Reaction between the silanediol (HO)(2)Si(OtBu)(2) and gallium amides, LGaCl(NHtBu) and LGa(NHEt)(2) (L = [HC{C(Me)N(Ar)}(2)](-), Ar = 2,6-iPr(2)C(6)H(3)), respectively, resulted in the facile isolation of molecular gallosilicates LGaCl(μ-O)Si(OH)(OtBu)(2) (1) and LGa(NHEt)(μ-O)Si(OH)(OtBu)(2) (2). Compound 2 easily reacts with 1 equiv of water to form the unique gallosilicate-hydroxide LGa(OH·THF)(μ-O)Si(OH)(OtBu)(2) (3). Compounds 1-3 contain the simple Ga-O-SiO(3) framework and are the first structurally authenticated molecular gallosilicates. These compounds may be used not only as models for gallosilicate-based materials but also as further reagents because of the presence of reactive functional groups attached to both gallium and silicon atoms. Accordingly, seven molecular heterometallic compounds were obtained from the reactions between compound 3 and group 4 amides M(NMe(2))(4) (M = Ti, Zr) or M(NEt(2))(4) (M = Ti, Zr, Hf). Hence, by tuning the reactions conditions and stoichiometries, it was possible to isolate and structurally characterize the complete 1:1 and 2:1 series (4-10). Completely inorganic cores of types M-O-Ga-O-Si-O and spiro M[O-Ga-O-Si-O](2) were obtained and characterized by common spectroscopic techniques.

Sterically controlled mechanochemistry under hydrostatic pressure

Mechanical stimuli can modify the energy landscape of chemical reactions and enable reaction pathways, offering a synthetic strategy that complements conventional chemistry. These mechanochemical mechanisms have been studied extensively in one-dimensional polymers under tensile stress using ring-opening and reorganization, polymer unzipping and disulfide reduction as model reactions. In these systems, the pulling force stretches chemical bonds, initiating the reaction. Additionally, it has been shown that forces orthogonal to the chemical bonds can alter the rate of bond dissociation. However, these bond activation mechanisms have not been possible under isotropic, compressive stress (that is, hydrostatic pressure). Here we show that mechanochemistry through isotropic compression is possible by molecularly engineering structures that can translate macroscopic isotropic stress into molecular-level anisotropic strain. We engineer molecules with mechanically heterogeneous components—a compressible (‘soft’) mechanophore and incompressible (‘hard’) ligands. In these ‘molecular anvils’, isotropic stress leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. Conversely, rigid ligands in steric contact impede relative motion, blocking reactivity. We combine experiments and computations to demonstrate hydrostatic-pressure-driven redox reactions in metal–organic chalcogenides that incorporate molecular elements that have heterogeneous compressibility, in which bending of bond angles or shearing of adjacent chains activates the metal–chalcogen bonds, leading to the formation of the elemental metal. These results reveal an unexplored reaction mechanism and suggest possible strategies for high-specificity mechanosynthesis.