Silvano Del Gobbo

Ag29(BDT)12(TPP)4: A Tetravalent Nanocluster

The bottom-up assembly of nanoparticles into diverse ordered solids is a challenge because it requires nanoparticles, which are often quasi-spherical, to have interaction anisotropy akin to atoms and molecules. Typically, anisotropy has been introduced by changing the shape of the inorganic nanoparticle core. Here, we present the design, self-assembly, optical properties, and total structural determination of Ag29(BDT)12(TPP)4, an atomically precise tetravalent nanocluster (NC) (BDT, 1,3-benzenedithiol; TPP, triphenylphosphine). It features four unique tetrahedrally symmetrical binding surface sites facilitated by the supramolecular assembly of 12 BDT (wide footprint bidentate thiols) in the ligand shell. When each of these sites was selectively functionalized by a single phosphine ligand, particle stability, synthetic yield, and the propensity to self-assemble into macroscopic crystals increased. The solid crystallized NCs have a substantially narrowed optical band gap compared to that of the solution state, suggesting strong interparticle electronic coupling occurs in the solid state.

Optoelectronic and photovoltaic properties of the air-stable organohalide semiconductor (CH3NH3)3Bi2I9

Lead halide perovskite materials have shown excellent optoelectronic as well as photovoltaic properties. However, the presence of lead and the chemical instability relegate lead halide perovskites to research applications only. Here, we investigate an emerging lead-free and air stable compound (CH3NH3)3Bi2I9 as a non-toxic potential alternative to lead halide perovskites. We have synthesized thin films, powders and millimeter-scale single crystals of (CH3NH3)3Bi2I9 and investigated their structural and optoelectronic properties. We demonstrate that the degree of crystallinity strongly affects the optoelectronic properties of the material, resulting in significantly different band gaps in polycrystalline thin films and single crystals. Surface photovoltage spectroscopy reveals outstanding photocharge generation in the visible (<700 nm) region, while transient absorption spectroscopy and space charge limited current measurements point to a long exciton lifetime and a high carrier mobility, respectively, similar to lead halide perovskites pointing to the remarkable potential of this semiconductor. Photovoltaic devices fabricated using this material yield a low power conversion efficiency (PCE) to date, but the PCE is expected to increase with improvements in thin film processing and device engineering.

The Silicon:Colloidal Quantum Dot Heterojunction

A heterojunction between crystalline silicon and colloidal quantum dots (CQDs) is realized. A special interface modification is developed to overcome an inherent energetic band mismatch between the two semiconductors, and realize the efficient collection of infrared photocarriers generated in the CQD film. This junction is used to produce a sensitive near infrared photodetector.

Tethering Metal Ions to Photocatalyst Particulate Surfaces by Bifunctional Molecular Linkers for Efficient Hydrogen Evolution

A simple and versatile method for the preparation of photocatalyst particulates modified with effective cocatalysts is presented; the method involves the sequential soaking of photocatalyst particulates in solutions containing bifunctional organic linkers and metal ions. The modification of the particulate surfaces is a universal and reproducible method because the molecular linkers utilize strong covalent bonds, which in turn result in modified monolayer with a small but controlled quantity of metals. The photocatalysis results indicated that the CdS with likely photochemically reduced Pd and Ni, which were initially immobilized via ethanedithiol (EDT) as a linker, were highly efficient for photocatalytic hydrogen evolution from Na2S-Na2SO3-containing aqueous solutions. The method developed in this study opens a new synthesis route for the preparation of effective photocatalysts with various combinations of bifunctional linkers, metals, and photocatalyst particulate materials.

Microwave-synthesized tin oxide nanocrystals for low-temperature solution-processed planar junction organo-halide perovskite solar cells

Tin oxide has been demonstrated to possess outstanding optoelectronic properties such as optical transparency and high electron mobility; therefore, it was successfully utilized as an electron transporting layer in various kinds of solar cells. In this study, for the first time, highly dispersible SnO2 nanoparticles were synthesized by a microwave-assisted non-aqueous sol–gel route in an organic medium. Ethanol dispersion of the as-prepared nanoparticles was used to cast a uniform thin layer of SnO2 without the aid of an aggregating agent and at low temperatures. Organohalide perovskite solar cells were fabricated using SnO2 as the electron transporting layer. Morphological and spectroscopic investigations, in addition to the good photoconversion efficiency obtained, evidenced that the nanoparticles synthesized by this route have optimal properties such as small size and crystallinity to form a continuous film. Furthermore, this method allows high reproducibility and scalability of the film deposition process.

Colloidal Sb2S3 nanocrystals: synthesis, characterization and fabrication of solid-state semiconductor sensitized solar cells

Inorganic nanocrystals composed of earth-abundant and non-toxic elements are crucial to fabricate sustainable photovoltaic devices on a large scale. In this study, various shapes and different phases of antimony sulfide nanocrystals, which are composed of non-scarce and non-toxic elements, are synthesized using a colloidal hot-injection method. The effect of various synthetic parameters on the final morphology is explored. Also, foreign ion (chlorine) effects on the morphology of Sb2S3 nanocrystals have been observed. Structural, optical and morphological properties of the nanocrystals were investigated, and Sb2S3 nanocrystal-based solid-state semiconductor-sensitized solar cells were fabricated using the as-prepared nanocrystals. We achieved a promising power conversion efficiency of 1.48%.