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.

Distinct photocatalytic performance was observed when Ta 3 N 5 was synthesized from commercially available Ta 2 O 5 or from Ta 2 O 5 prepared from TaCl 5 via the sol−gel route. With respect to photocatalytic O 2 evolution with Ag + as a sacrificial reagent, the Ta 3 N 5 produced from commercial Ta 2 O 5 exhibited higher activity than the Ta 3 N 5 produced via the sol−gel route. When the Ta 3 N 5 photocatalysts were decorated with Pt nanoparticles in a similar manner, the Ta 3 N 5 from the sol−gel route exhibited higher photocatalytic hydrogen evolution activity from a 10% aqueous methanol solution than Ta 3 N 5 prepared from commercial Ta 2 O 5 where no hydrogen can be detected. Detailed surface and bulk characterizations were conducted to obtain fundamental insight into the resulting photocatalytic activities. The characterization techniques, including XRD, elemental analysis, Raman spectroscopy, UV−vis spectroscopy, and surface-area measurements, revealed only negligible differences between these two photocatalysts. Our thorough characterization of the surface properties demonstrated that the very thin outermost layer of Ta 3 N 5 , with a thickness of a few nanometers, consists of either the reduced state of tantalum (TaN) or an amorphous phase. The extent of this surface layer was likely dependent on the nature of precursor oxide surfaces. DFT calculations based on partially oxidized Ta 3 N 4.83 O 0.17 and N deficient Ta 3 N 4.83 consisting of reduced Ta species well described the optoelectrochemical properties obtained from the experiments. Electrochemical and Mott−Schottky analyses demonstrated that the surface layer drastically affects the energetic picture at the semiconductor−electrolyte interface, which can consequently affect the photocatalytic performance. Chemical etching of the surface of Ta 3 N 5 particles to remove this surface layer unites the photocatalytic properties with the photocatalytic performance of these two materials. Mott−Schottky plots of these chemically etched Ta 3 N 5 materials exhibited similar characteristics. This result suggests that the surface layer (1−2 nm) determines the electrochemical interface, which explains the different photocatalytic performances of these two materials.

A lead-free and air-stable organohalide semiconductor exhibiting noteworthy optoelectronic properties is investigated. With improvements in thin film processing, this material is expected to yield good solar cell efficiency.

Chemical bath deposition (CBD) of tin oxide (SnO) thin films as an electron-transport layer (ETL) in a planar-heterojunction n-i-p organohalide lead perovskite and organic bulk-heterojunction (BHJ) solar cells is reported. The amorphous SnO (a-SnO) films are grown from a nontoxic aqueous bath of tin chloride at a very low temperature (55 °C) and do not require postannealing treatment to work very effectively as an ETL in a planar-heterojunction n-i-p organohalide lead perovskite or organic BHJ solar cells, in lieu of the commonly used ETL materials titanium oxide (TiO) and zinc oxide (ZnO), respectively. Ultraviolet photoelectron spectroscopy measurements on the glass/indium-tin oxide (ITO)/SnO/methylammonium lead iodide (MAPbI)/2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene device stack indicate that extraction of photogenerated electrons is facilitated by a perfect alignment of the conduction bands at the SnO/MAPbI interface, while the deep valence band of SnO ensures strong hole-blocking properties. Despite exhibiting very low electron mobility, the excellent interfacial energetics combined with high transparency (E > 4 eV) and uniform substrate coverage make the a-SnO ETL prepared by CBD an excellent candidate for the potentially low-cost and large-scale fabrication of organohalide lead perovskite and organic photovoltaics.