Inverted Perovskite Photovoltaics Using Flame Spray Pyrolysis Solution Based CuAlO2/Cu-O Hole-Selective Contact.

We present the functionalization process of a conductive and transparent CuAlO2/Cu-O hole-transporting layer (HTL). The CuAlO2/Cu-O powders were developed by flame spray pyrolysis and their stabilized dispersions were treated by sonication and centrifugation methods. We show that when the supernatant part of the treated CuAlO2/Cu-O dispersions is used for the development of CuAlO2/Cu-O HTLs the corresponding inverted perovskite-based solar cells show improved functionality and power conversion efficiency of up to 16.3% with negligible hysteresis effect.

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells.

A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is interface loss in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials without compromising efficiency, stability, or scalability of perovskite solar cells. Tantalum-doped tungsten oxide (Ta-WO x )/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. In a simple device with regular planar architecture and a self-assembled monolayer, Ta-WO x -doped interface-based perovskite solar cells achieve maximum efficiencies of 21.2% and offer more than 1000 hours of light stability. By eliminating additional ionic dopants, these findings open up the entire class of organics as scalable hole-transporting materials for perovskite solar cells.

Overcoming the Interface Losses in Planar Heterojunction Perovskite-Based Solar Cells.

A scalable, hysteresis-free and planar architecture perovskite solar cell is presented, employing a flame spray synthesized low-temperature processed NiO (LT-NiO) as hole-transporting layer yielding efficiencies close to 18%. Importantly, it is found that LT-NiO boosts the limits of open-circuit voltages toward an impressive non-radiative voltage loss of 0.226 V only, whereas PEDOT: PSS suffers from significant large non-radiative recombination losses.

Effective ligand passivation of Cu2O nanoparticles through solid-state treatment with mercaptopropionic acid.

In colloidal nanoparticle (NPs) devices, trap state densities at their surface exert a profound impact on the rate of charge carrier recombination and, consequently, on the deterioration of the device performance. Here, we report on the successful application of a ligand exchange strategy to effectively passivate the surface of cuprite (Cu2O) NPs. Cu2O NPs were prepared by means of a novel synthetic route based on flame spray pyrolysis. FTIR, XRD, XPS, and HRTEM measurements corroborate the formation of cubic cuprite Cu2O nanocrystals, excluding the possible presence of undesired CuO or Cu phases. Most importantly, steady-state emission and transient absorption assays document that surface passivation results in substantial changes in the intensity of emissive excitonic states--centered at copper and oxygen vacancies--and in the lifetime of excitons near the band edge. To shed light onto ultrafast processes in Cu2O nanocrystals additional pump probe experiments on the femtosecond and nanosecond time scales were carried out. Two discernible species were observed: on one hand, an ultrafast component (~ps) that relates to the excitons; on the other hand, a long-lived component (~µs) that originates from the defects/trap states.

Nanocomposites of high-density polyethylene with amorphous calcium phosphate: in vitro biomineralization and cytocompatibility of human mesenchymal stem cells.

Polyethylene is widely used as a component of implants in medicine. Composites made of high-density polyethylene (HDPE) containing different amounts of amorphous calcium phosphate nanoparticles were investigated concerning their in vitro biomedical performance. The nanoparticles were produced by flame spray synthesis and extruded with HDPE, the latter complying with Food and Drug Administration regulations. Mechanical properties such as Young's modulus and contact angle as well as in vitro biomineralization of the nanocomposites hot-pressed into thin films were evaluated. The deposition of a hydroxyapatite layer occurred upon immersion in simulated body fluid. Additionally, a cell culture study with human mesenchymal stem cells for six weeks allowed a primary assessment of the cytocompatibility. Viability assays (alamarBlue and lactate dehydrogenase detection) proved the absence of cytotoxic effects of the scaffolds. Microscopic images after hematoxylin and eosin staining confirmed typical growth and morphology. A preliminary experiment analyzed the alkaline phosphatase activity after two weeks. These findings motivate further investigations on bioactive HDPE in bone tissue engineering.

Electrical resistivity of assembled transparent inorganic oxide nanoparticle thin layers: influence of silica, insulating impurities, and surfactant layer thickness.

The electrical properties of transparent, conductive layers prepared from nanoparticle dispersions of doped oxides are highly sensitive to impurities. Production of cost-effective thin conducting films for consumer electronics often employs wet processing such as spin and/or dip coating of surfactant-stabilized nanoparticle dispersions. This inherently results in entrainment of organic and inorganic impurities into the conducting layer leading to largely varying electrical conductivity. Therefore, this study provides a systematic investigation on the effect of insulating surfactants, small organic molecules and silica in terms of pressure dependent electrical resistivity as a result of different core/shell structures (layer thickness). Application of high temperature flame synthesis gives access to antimony-doped tin oxide (ATO) nanoparticles with high purity. This well-defined starting material was then subjected to representative film preparation processes using organic additives. In addition ATO nanoparticles were prepared with a homogeneous inorganic silica layer (silica layer thickness from 0.7 to 2 nm). Testing both organic and inorganic shell materials for the electronic transport through the nanoparticle composite allowed a systematic study on the influence of surface adsorbates (e.g., organic, insulating materials on the conducting nanoparticle's surface) in comparison to well-known insulators such as silica. Insulating impurities or shells revealed a dominant influence of a tunneling effect on the overall layer resistance. Mechanical relaxation phenomena were found for 2 nm insulating shells for both large polymer surfactants and (inorganic) SiO(2) shells.

Porous polysulfone coatings for enhanced drug delivery.

The synthesis of a porous polysulfone (PSU) coating for use in drug delivery applications is presented. PSU can serve as a functional surface coating for drug delivery vehicles, such as intraocular biomicrorobots. The coatings can be applied using spin coating or dip coating. The porosity is introduced by selectively dissolving calcium carbonate nanoparticles embedded in the bulk polymer. The network of pores thus formed increases by a factor of thirty the amount of Rhodamine B (model drug) that can be loaded and by a factor of fifteen the amount that can be released. The films do not affect cell viability and exhibit poor cell adhesion. The straightforward synthesis and predictability of porosity enables the tuning of the amount of drug that can be loaded.

Phosphate starvation as an antimicrobial strategy: the controllable toxicity of lanthanum oxide nanoparticles.

Lanthanum oxide nanoparticles were utilized to scavenge phosphate from microbial growth media for the use of targeted nutrient starvation as an antimicrobial strategy. Only in phosphate poor environments a toxic effect was observed. The effect was shown on Escherichia coli, Staphylococcus carnosus, Penicillium roqueforti, and Chlorella vulgaris.

Exposure to engineered nanoparticles: Model and measurements for accident situations in laboratories.

In the life cycle of engineered nanoparticles (ENP), their manufacturing requires particular attention because of unwanted potential ENP emissions to workplaces. We simulated three scenarios of equipment failure during gas phase production of nanoparticles in a laboratory. The emission plume of nanoparticles was tracked with high spatial and temporal resolution by 10 measurement devices. While under normal production conditions, no elevated ENP concentrations were observed, worst case scenarios led to homogeneous indoor ENP concentrations of up to 10(6)cm(-3) in a 300m(3) production room after only 60s. The fast dispersal in the room was followed by an exponential decrease in number concentration after the emission event. Under conditions like those observed - rapid dispersal and good mixing - a single measurement device alone can provide valuable information for an ENP exposure assessment. A one-box model adequately reflected measured number concentrations (r(2)>0.99). The ENP emission rates to the workplace were estimated between 2.5·10(11) and 6·10(12)s(-1) for the three emission scenarios. The worst case emission rate at the production zone was also estimated at 2·10(13)s(-1) with a stoichiometric calculation based on the precursor input, density and particle size. ENP intake fractions were 3.8-5.1·10(-4) inhaled ENP per produced ENP in the investigated setting. These could only be substantially lowered by leaving the production room within a few minutes after the emission event.

Two-layer membranes of calcium phosphate/collagen/PLGA nanofibres: in vitro biomineralisation and osteogenic differentiation of human mesenchymal stem cells.

The present study evaluates the in vitro biomedical performance of an electrospun, flexible, anisotropic bilayer with one layer containing a collagen to mineral ratio similar to that in bone. The double membrane consists of a poly(lactide-co-glycolide) (PLGA) layer and an amorphous calcium phosphate (a-CaP)/collagen (Col)/PLGA layer. In vitro biomineralisation and a cell culture study with human mesenchymal stem cells (hMSC) were conducted to characterise such membranes for possible application as biomaterials. Nanofibres with different a-CaP/Col/PLGA compositions were synthesised by electrospinning to mimic the actual composition of bone tissue. Immersion in simulated body fluid and in cell culture medium resulted in the deposition of a hydroxyapatite layer. Incubation of hMSC for 4 weeks allowed for assessment of the proliferation and osteogenic differentiation of the cells on both sides of the double membrane. Confocal laser scanning microscopy was used to observe the proper adhesion of the cells. Calcium and collagen content was proven by Alizarin red S and Sirius red assays. Acute cytotoxic effects of the nanoparticles or the chemicals used in the scaffold preparation could be excluded based on viability assays (alamarBlue and alkaline phosphatase activity). The findings suggest possible application of such double membranes is in treatment of bone defects with complex geometries as wound dressing material.

Light-curable polymer/calcium phosphate nanocomposite glue for bone defect treatment.

Light-curable, methacrylate-based resins are clinically used for complex defect repair in dentistry (Heliobond). The present study investigates how such easy-to-apply polymers may be used on a much broader range of applications, particularly for gluing wet bone. We investigate the significantly improved adhesion of the polymer to wet bone surfaces in a close to in vivo setup using freshly cut cow hip bone as a model. The use of a reactive filler (20 wt.% amorphous, glassy calcium phosphate nanoparticles, a-CaP) allows for combination of the properties of the polymer (strength; light-curing) and the reactive filler (recrystallization of amorphous CaP to hydroxyapatite within minutes). This filler alone has been earlier suggested for use as an injectable bone cement since it reacts under in vivo conditions within 10-15 min. Our study transfers this reactivity into a composite, thus using the reactive CaP phase to establish an improved adhesion of the composite to wet bone surfaces. Additional in vitro bioactivity tests, compressive and tensile strength suggest use of such light-curable nanocomposites for complex-shaped load-bearing implant materials and fracture repair.

Graphene-stabilized copper nanoparticles as an air-stable substitute for silver and gold in low-cost ink-jet printable electronics.

Metallic copper nanoparticles were synthesized by a bottom-up approach, and in situ coated with protective shells of graphene in order to get a metal nanopowder of high air stability and chemical inertness. Using an amphiphilic surfactant, a water-based copper nanocolloid could be prepared and successfully printed onto a polymer substrate by conventional ink-jet printing using household printers. The dried printed patterns exhibited strong metallic gloss and an electrical conductivity of >1 S cm(-1) without the need for a sintering or densification step. This conductivity currently limits use in electronics to low current application or shielding and decorative effects. The high stability of graphene-coated copper nanoparticles makes them economically a most attractive alternative to silver or gold nanocolloids, and will strongly facilitate the industrial use of metal nanocolloids in consumer goods.

Highly sensitive optical detection of humidity on polymer/metal nanoparticle hybrid films.

Porous metal films for optical humidity sensing were prepared from copper nanoparticles protected by a 2-3 nm carbon coating, a silicon tenside, and a polymeric wetting agent. Exposure to water or solvent vapor revealed an exceptional sensitivity with optical shifts in the visible light range of up to 50 nm for a change of 1% in relative humidity. These properties could be attributed to a combination of surface plasmon resonance effects at low humidity and thin film interference at higher water or solvent concentration in the surrounding air. The simple concept and use of ultra-low-cost materials suggests application of such porous metal-film-based optical humidity sensors in large-scale applications for food handling, storage, and transport.