We describe a seeded hydrothermal process for the growth of unique double-sided brush-shaped (DSBS) TiO2 nanostructure assemblies consisting of highly ordered rutile nanowires vertically aligned around an annealed TiO2 nanoparticle layer. The annealed TiO2 nanoparticle layer seeds the nanowire growth and also supports the DSBS structure. The morphology of the DSBS TiO2 nanostructure depends on the hydrothermal reaction time. The diameter of the nanowires is about 6.6 nm, and with increasing reaction time from 1 to 8 h the nanowire length increases from 0.6 to 6.2 μm, whereas the thickness of the nanoparticle layer decreases from 4.3 to 2.8 μm. These free-standing nanowire arrays provide large internal surface area, which is essential for minimizing carrier recombination in high performance photovoltaic devices. Furthermore, the nanowire architecture can help increase the rate of charge transport as compared to particulate films because of lower concentration of grain boundaries. The power conversion efficiency of backside (DSBS TiO2/FTO photoanode) illuminated dye-sensitized solar cells fabricated using the DSBS TiO2 nanostructure assembly is found to be depended on the nanowire length. A cell fabricated using 15.2 μm thick nanostructures sensitized by N719 has a short-circuit current density of 12.18 mA cm–2, 0.78 V open circuit potential, and a 0.59 filling factor, yielding a maximum power conversion efficiency of 5.61% under AM 1.5 illumination.Keywords: dye-sensitized solar cells; hydrothermal synthesis; nanostructure; nanowire arrays; TiO2;

•La-doped SrTiO3 ceramics with Nb-doped grain boundaries were prepared.•Seebeck coefficient was increased effectively relative to normal La-doped SrTiO3.•Power factor was increased by 35% as compared with normal La-doped SrTiO3 ceramics.•Energy filtering effect due to the band offset at grain boundaries was analyzed.•The strategy is particularly applicable in thermoelectric polycrystalline ceramics.We report on an effective increase in the Seebeck coefficient for 5% La-doped SrTiO3 nanoceramics at temperatures of 300–800 K through grain boundary doping with Nb, which results in an improvement of power factor by a value as high as 35%. This enhancement is likely due to the energy filtering effect at the Nb-doped grain boundaries with an enhanced potential barrier originating from the band offset between the boundaries and the interior of the grains.

We report on low-cost, all solution fabrication of efficient air-stable nanostructured thin film photovoltaics comprised of n-type Sb2S3 chemically deposited onto TiO2 nanowire array films, forming coaxial Sb2S3/TiO2 nanowire hybrids vertically oriented from the SnO2:F coated glass substrate, which are then intercalated with poly(3-hexylthiophene) (P3HT) for hole transport and enhanced light absorption.

Cu2FeSnS4 (CFTS) nanocrystals with tunable crystal phase have been synthesized using a solution-based method. As-synthesized CFTS nanocrystals in the shape of oblate spheroid and triangular plate with band gaps of 1.54 ± 0.04 and 1.46 ± 0.03 eV, respectively, appear attractive as a low-cost substitute for thin film solar cells.

ZnO tubes with diameters ranging from tens of nanometers to several microns were prepared via hydrothermal reactions using surfactants as structure-directing agents. All tubular ZnO materials are indexed to a hexagonal structure of wurtzite. The room-temperature photoluminescence spectra of ZnO tubes reveal a strong UV emission at around 387 nm and broad and a relative weak visible emission with main peak identified at 510–520 nm, depending on the size of ZnO tubes.Highlights► ZnO tubes with tunable sizes. ► Self-assemble synthesis under hydrothermal condition. ► Size-dependent optical properties.

Monodisperse wurtzite CuInxGa1–xS2 nanocrystals have been synthesized over the entire composition range using a facile solution-based method. Depending on the chemical composition and synthesis conditions, the morphology of the nanocrystals can be controlled in the form of bullet-like, rod-like, and tadpole-like shapes. The band gap of the nanocrystals increases linearly with increasing Ga concentration, with band gap values for the end members being close to those observed in the bulk. Colloidal suspensions of the nanocrystals are attractive for use as inks for low-cost fabrication of thin film solar cells by spin or spray coating.

The formation mechanisms of self-organized anodic titania nanotube arrays have been widely studied with an aim towards enabling precise control of nanotube array morphology and properties, thereby allowing control of fabrication parameters for optimal performance of the resulting films in their given application. Building upon recent work [S. Yoriya and C. A. Grimes, J. Mater. Chem., 2011, 21, 102–108], we elucidate the self-ordering and porosity of nanoporous and nanotubular anodic titania films as a function of anodization conditions.

A variety of inorganic materials with amazingly complex structures and morphologies are produced by natural organisms. The fundamental mechanism underlying the natural biological synthesis of inorganic materials can be ascribed to the unique recognition and interaction of proteins with specific inorganic species. By mimicking natural biomineralization, genetically engineered proteins have in recent years been successfully utilized as platforms for the synthesis of inorganic nanostructures of various compositions under mild reaction conditions. Moreover, the precisely oriented assembly of genetically engineered proteins offers flexibility in designing inorganic nanostructures with desired complex architecture. This short review summarizes the recent progress in materials design using genetically engineered protein templates.

High surface area highly ordered nanoporous thin films are the current gold standard for gas sensor use, however the nanostructure of such films is prone to collapse at annealing temperatures as low as 250 °C resulting in formation of a dense layer of limited utility. We report on a templating method used to deposit highly ordered nanoporous platinum (Pt)-doped tin dioxide (SnO2) thin films that are crystallized by a 100 °C water vapor hydrothermal treatment, with the low temperature process being compatible with a large variety of substrates including plastic. The resulting highly ordered nanoporous, transparent Pt–SnO2 thin films are mechanically stable and can be annealed, as desired, at temperatures up to 800 °C for removal of the templating materials and tailoring of gas sensitivities without damage to the nanoporous structure. The synthesis method is general, offering a promising strategy for preparing high performance nanoporous metal oxide crystalline films for applications including gas sensing, photocatalysis, and 3rd generation photovoltaics. In our example application of the synthesized materials, we find that these Pt–SnO2 films exhibit exceptional hydrogen gas sensing behavior, rapidly detecting low-level hydrogen concentrations at room temperature; for example, an eight order of magnitude change in electrical resistance is seen in response to 10000 ppm H2, with only minimal sensitivity to humidity.

Monodisperse CuInS2 nanocrystals are produced by injecting mixed metal-oleate precursors into hot organic solvents containing the dissolved sulphur sources. A better understanding of the formation mechanism of CuInS2 has enabled us to tailor anisotropic shapes in the form of triangular-pyramid, circular cone, and bullet-like rods with tunable crystal phases by varying the synthetic conditions.

Cu2FeSnS4 (CFTS) nanocrystals with tunable crystal phase have been synthesized using a solution-based method. As-synthesized CFTS nanocrystals in the shape of oblate spheroid and triangular plate with band gaps of 1.54 ± 0.04 and 1.46 ± 0.03 eV, respectively, appear attractive as a low-cost substitute for thin film solar cells.

Monodisperse CuInS2 nanocrystals are produced by injecting mixed metal-oleate precursors into hot organic solvents containing the dissolved sulphur sources. A better understanding of the formation mechanism of CuInS2 has enabled us to tailor anisotropic shapes in the form of triangular-pyramid, circular cone, and bullet-like rods with tunable crystal phases by varying the synthetic conditions.

We report on low-cost, all solution fabrication of efficient air-stable nanostructured thin film photovoltaics comprised of n-type Sb2S3 chemically deposited onto TiO2 nanowire array films, forming coaxial Sb2S3/TiO2 nanowire hybrids vertically oriented from the SnO2:F coated glass substrate, which are then intercalated with poly(3-hexylthiophene) (P3HT) for hole transport and enhanced light absorption.

The formation mechanisms of self-organized anodic titania nanotube arrays have been widely studied with an aim towards enabling precise control of nanotube array morphology and properties, thereby allowing control of fabrication parameters for optimal performance of the resulting films in their given application. Building upon recent work [S. Yoriya and C. A. Grimes, J. Mater. Chem., 2011, 21, 102–108], we elucidate the self-ordering and porosity of nanoporous and nanotubular anodic titania films as a function of anodization conditions.

A variety of inorganic materials with amazingly complex structures and morphologies are produced by natural organisms. The fundamental mechanism underlying the natural biological synthesis of inorganic materials can be ascribed to the unique recognition and interaction of proteins with specific inorganic species. By mimicking natural biomineralization, genetically engineered proteins have in recent years been successfully utilized as platforms for the synthesis of inorganic nanostructures of various compositions under mild reaction conditions. Moreover, the precisely oriented assembly of genetically engineered proteins offers flexibility in designing inorganic nanostructures with desired complex architecture. This short review summarizes the recent progress in materials design using genetically engineered protein templates.