Paul G. O'Brien

York University · Department of Mechanical Engineering

Radiative cooling (RC) can provide free cooling by emitting radiative heat into outer space. This article presents the effects of solar radiation, non-radiative heat gains, atmospheric conditions, and spectral selectivity on the performance of radiative cooling technologies. Radiative cooling materials, including polymeric structures, pigmented pai...

Herein we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor...

Herein we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor...

Herein, we present an optical cavity in the form of a prolate ellipsoid that can greatly enhance the performance of solar thermophotovoltaic (STPV) systems. The geometrical parameters of the cavity can be designed to control the degree of photon recycling, the temperature of the emitter within the STPV system, gap distance and effective view factor...

The full utilization of broadband solar irradiance is becoming increasingly useful for applications such as long-term space missions, wherein power generation from external sources and regenerative life support systems are essential. Luminescent solar concentrators (LSCs) can be designed to separate sunlight into photosynthetically active radiation...

This paper computationally explores the optical response of various designs of one-dimensional photonic crystal optical filters comprised of alternating layers of dense zirconia and zirconia aerogel. COMSOL Multiphysics software is used to assess the optical characteristics of the filters. The performance of the filters within a thermophotovoltaic...

High temperature solar receivers can convert concentrated solar power to heat to drive chemical production or mechanical cycles to produce electricity. Transparent windows with selective coatings that reflect thermal radiation can be used to cover receivers to improve their efficiency. However, in parabolic dish concentrators (PDC) these windows ca...

There is potential to significantly reduce CO2 emissions by increasing the efficiency and reducing the duty cycle of HVAC systems by using smart booster fans and dampers. Smart booster fans fit in the vents within a home, operating quietly on low power (2W) to augment HVAC systems and improve their performance. In this study, a prototype duct syste...

Microalgae has potential for large-scale biofuel production and CO2 remediation, however its growth is energy intensive and easily hindered by contamination, unsuitable conditions, and photosaturation. To mitigate these problems the solar irradiance can be partitioned into photosynthetically active radiation (PAR) and photosynthetically inactive ra...

Luminescent solar concentrators (LSCs) are a promising technology for integration and renewable energy generation in buildings because they are inexpensive, lightweight, aesthetically versatile, can concentrate both direct and diffuse light and offer wavelength-selective transparency. LSCs have been extensively investigated for applications involvi...

Solar-driven evaporation is a promising technology with many potential applications including desalination, power generation, purification, sterilization and phase separation. Recently, much research has been directed towards increasing solar-driven evaporation efficiencies with photothermal materials that reside at the air-water interface to provi...

Numerical calculations are performed to determine the potential of using one-dimensional transparent photonic crystal heat mirrors (TPCHMs) as transparent coatings for solar receivers. At relatively low operating temperatures of 500 K, the TPCHMs investigated herein do not provide a significant advantage over conventional transparent heat mirrors t...

Solar-driven CO2 hydrogenation can provide a renewable source of fuels and reduce greenhouse gas emissions if operated at industrial scales. Herein we investigate the photomethanation (light-driven Sabatier reaction) rates over Ru films sputtered onto silica opal (Ru/SiO2) and inverted silicon opal photonic crystal (Ru/i-Si-o) supports at ambient t...

Herein we present the design of infrared mirror coatings for the enhanced performance of incandescent lighting. We consider single and stacked dielectric mirrors comprised of alternating layers of TCO and SiO2 nanoparticle films to function as infrared mirrors that reduce heat losses in incandescent lights. In this work, thin-film theory was employ...

In article number 1702277, Geoffrey A. Ozin and co‐workers report that the photomethanation of CO2 over highly dispersed nanostructured RuO2 catalysts on 3D silicon photonic crystal supports achieves impressive conversion rates as high as 4.4 mmol gcat⁻¹ h⁻¹ at ambient temperatures under high‐intensity solar simulated irradiation. This performance...

Sunlight-driven catalytic hydrogenation of CO2 is an important reaction that generates useful chemicals and fuels and if operated at industrial scales can decrease greenhouse gas CO2 emissions into the atmosphere. In this work, the photomethanation of CO2 over highly dispersed nanostructured RuO2 catalysts on 3D silicon photonic crystal supports, a...

The size dependence of the photothermal effect of palladium nanocrystals enables the selectivity of the solar powered heterogeneous catalytic hydrogenation of carbon dioxide to be finely tailored towards producing either carbon monoxide through the reverse water gas shift reaction, CO2 + H2 → CO + H2O, favored for small nanocrystals or to methane,...

This study has designed and implemented a library of hetero-nanostructured catalysts, denoted as Pd@Nb2O5, comprised of size-controlled Pd nanocrystals interfaced with Nb2O5 nanorods. This study also demonstrates that the catalytic activity and selectivity of CO2 reduction to CO and CH4 products can be systematically tailored by varying the size of...

Herein quantum efficiency enhancements are demonstrated in multi-junction solar cells with one-dimensional Selectively Transparent and Conducting Photonic Crystal (STCPC) intermediate Bragg reflectors. Specifically, the modelling, design and fabrication of series-connected multi-junction cells comprising a top amorphous-silicon cell and a bottom cr...

Some Like It Hot: Geoffry A. Ozin and co-workers demonstrate that the reverse water gas shift (RWGS) reaction, driven by a visible and near infrared responsive Pd@Nb2O5 is thermally activated with measured conversion rates as high as 1.8 mmol gcat⁻¹ h⁻¹, in article 1600189. Specifically, the RWGS reaction is enabled by heat generated from thermaliz...

TiOx (x < 2) nanoparticles with tunable colors from white to gray to blue–gray to black are synthesized by magnesium (Mg) reduction of white P25 TiO2 nanocrystals followed by removal of excess Mg with aqueous HCl and distilled water. Increasing amounts of Mg smoothly decrease the oxygen content in TiOx which is responsible for the gradual increase...

The field of solar fuels seeks to harness abundant solar energy by driving useful molecular transformations. Of particular interest is the photo-driven conversion of greenhouse gas CO2 into carbon-based fuels and chemical feedstocks, with the ultimate goal of providing a sustainable alternative to traditional fossil-fuels. Highly defected indium ox...

Four different polymorphs of nanostructured iron oxyhydroxides, namely; goethite (?-FeOOH), akaganeite (?-FeOOH), lepidocrocite (?-FeOOH), and feroxyhyte (?-FeOOH) were synthesized and fully characterized by X-ray diffraction, electron microscopy, UV-Visible spectrophotometry, BET measurements and X-ray photoemission spectroscopy. The relationship...

Silicon constitutes 28% of the earth's mass. Its high abundance, lack of toxicity and low cost coupled with its electrical and optical properties, make silicon unique among the semiconductors for converting sunlight into electricity. In the quest for semiconductors that can make chemicals and fuels from sunlight and carbon dioxide, unfortunately th...

Supplementary

The reverse water gas shift (RWGS) reaction driven by Nb2O5 nanorod-supported Pd nanocrystals without external heating using visible and near infrared (NIR) light is demonstrated. By measuring the dependence of the RWGS reaction rates on the intensity and spectral power distribution of filtered light incident onto the nanostructured Pd@Nb2O5 cataly...

The development of strategies for increasing the lifetime of photoexcited charge carriers in nanostructured metal oxide semiconductors is important for enhancing their photocatalytic activity. Intensive efforts have been made in tailoring the properties of the nanostructured photocatalysts through different ways, mainly including band-structure eng...

Thermal treatment of ultrathin films of hematite (α-Fe2 O3 ) under an atmosphere of 5 % H2 in Ar is presented as a means of activating α-Fe2 O3 towards the photoelectrochemical splitting of water. Spin-coated films annealed in air exhibited no photoactivity, whereas films treated in hydrogen exhibited a photocurrent response. X-ray photoelectron sp...

Nanotower- and nanowall-like indium oxide structures were grown directly on fluorine-doped tin oxide (FTO)/In2O3 seeded substrates and pristine FTO substrates, respectively, by a straightforward solvothermal method. The tower-like nanostructures are proposed to form via a self-assembly process on the In2O3 seeds. The wall-like nanostructures are pr...

Nanotower- and nanowall-like indium oxide structures were grown directly on fluorine-doped tin oxide (FTO)/In2O3 seeded substrates and pristine FTO substrates, respectively, by a straightforward solvothermal method. The tower-like nanostructures are proposed to form via a self-assembly process on the In2O3 seeds. The wall-like nanostructures are pr...

The Inside Back cover picture shows ultrathin films of α-Fe2O3 before and after treatment in 5 % H2 in Ar at 450 °C. The hydrogen treatment creates oxygen vacancies in the iron oxide lattice, resulting in a non-stoichiometric hematite phase that is active for photoelectrochemical water oxidation. Electrochemical impedance spectroscopy reveals the b...

Gaseous CO2 is transformed photochemically and thermochemically in the presence of H2 to CH4 at millimole per hour per gram of catalyst conversion rates, using visible and near-infrared photons. The catalyst used to drive this reaction comprises black silicon nanowire supported ruthenium. These results represent a step towards engineering broadband...

The solar-to-chemical energy conversion of greenhouse gas CO2 into carbon-based fuels is a very important research challenge, with implications for both climate change and energy security. Herein, the key attributes of hydroxides and oxygen vacancies are experimentally identified in non-stoichiometric indium oxide nanoparticles, In2O3-x(OH)y, that...

Advances towards the vision of the “solar fuels refinery” of the future are portrayed in the cover art, based on article 1400013 by G. A. Ozin and co-workers. In the article, the attributes of hydroxide groups and oxygen vacancies are identified for non-stoichiometric indium oxide photocatalytic nanoparticles in the light-assisted, gas-phase conver...

Supplementary

The performance of optoelectronic devices using glass envelopes can be improved substantially by the application of an effective anti-reflective coating. In this paper, we investigate the preparation of low index films through modulation of the porosity of silica nanoparticle films. Porosity variation is accomplished by introducing polystyrene poro...

Herein we present nanoporous transparent and conducting films prepared by sputtering controlled amounts of ITO onto and into the interconnected pores of SiO2 and SnO2 nanoparticle films. The sheet resistance of these nanoporous transparent conducting films made with either SiO2 or SnO2 nanoparticles is less than 103 Ω/□. Furthermore, we demonstrate...

Thin semi-transparent hydrogenated amorphous silicon (a-Si:H) solar cells with selectively transparent and conducting photonic crystal (STCPC) back-reflectors are demonstrated. Short circuit current density of a 135 nm thick a-Si:H cell with a given STCPC back-reflector is enhanced by as much as 23% in comparison to a reference cell with an ITO fil...

See-through dye-sensitized solar cells with 1D photonic crystal Bragg reflector photoanodes show an increase in peak external quantum efficiency of 47% while still maintaining high fill factors, resulting in an almost 40% increase in power conversion efficiency. These photoanodes are ideally suited for tandem and building integrated photovoltaics.

The potential use of selectively transparent and conducting photonic crystals (STCPCs) made of ITO and silica nanoparticles as rear reflectors in 10 μm crystalline silicon (c-Si) photovoltaics (PV) have been explored. Optical simulations comparing the performance of STCPC-reflectors and aluminum reflectors have been performed. The STCPCs outperform...

We present herein an example of nanocrystalline antimony-doped tin oxide (nc-ATO) disordered macroporous "inverse opal" 3D electrodes as efficient charge-collecting support structures for the electrolysis of water using a hematite surface catalyst. The 3D macroporous structures were created via templating of polystyrene spheres, followed by infiltr...

A simple, green, robust, widely applicable, multi-gram and cost-effective 'one-pot' synthesis of aqueous dispersions of colloidally stable 3-6 nm TCO NPs using bare metal powder precursors is described, and their utilization for making TCO high surface area nanoporous films is also demonstrated, which speaks well for their usage in a wide range of...

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO2) nanoparticle films exhibit Bragg-reflectance peaks in the visible spectrum of 95% reflectivity and have a full width at half maximum that is greater than 200 nm. At the same time, their condu...

Wave-optics analysis is performed to show that selectively transparent and conducting photonic crystals (STCPCs) can be utilized as rear contacts to enhance the performance of building-integrated photovoltaics (BIPV). For instance, the current generated in an a-Si:H cell with an STCPC functioning as its rear contact is comparable to that of a simil...

A novel one-dimensional photonic crystal, called selectively transparent and conducting photonic crystal (STCPC), which integrates tunable optical and electrical properties is presented as a potential next-generation device element for advanced optoelectronics. A significant advance over existing 1D PCs, STCPCs combine intense wavelength selective...

We report herein on the integration of novel transparent and conducting one-dimensional photonic crystals that consist of periodically alternating layers of spin-coated antimony-doped tin oxide nanoparticles and sputtered tin-doped indium oxide into organic light emitting diode (OLED) microcavities. The large refractive index contrast between the l...

Unusually high loading of noble metal nanoparticles on nanostructured metal oxide surfaces, like inverse titania or tin oxide opals, was achieved by antimony doping of the metal oxide, which bodes well for their use as supports for heterogeneous catalysis and photocatalysis, chemical sensor, and solar cell applications.

Ultrathin Bi₂S₃ nanowires undergo a pronounced photothermal response to irradiation from a commercial camera flash. Controlled nano-welding was shown by using single walled carbon nanotube mats as an electrically and thermally conductive substrate. The resulting welded nanowire film is denser and has significantly lower resistance than unflashed bi...

Wave-optics analysis is performed to investigate the benefits of integrating photonic crystals into micromorph cells. Specifically, we theoretically investigate two novel micromorph cells which integrate photonic crystals and compare their optical performance with that of conventional micromorph cells. In the first innovative micromorph cell config...

Wave-optics analysis is performed to investigate the benefits of utilizing Bragg-reflectors and inverted ZnO opals as intermediate reflectors in micromorph cells. The Bragg-reflector and the inverted ZnO opal intermediate reflector increase the current generated in a 100 nm thick upper a-Si:H cell within a micromorph cell by as much as 20% and 13%,...

Selectively transmissive and conductive 1D photonic crystals (PCs) are fabricated by alternately depositing sputtered ITO and spin-coated ATO nanoparticle films. These Bragg reflectors exhibit broad and intense Bragg peaks (tunable via the thickness of their ITO layers) over their stop gap but are highly transmissive over remaining spectral regions...

Two attributes of opaline photonic crystal (PC) back-reflectors optically coupled to thin semiconductor films contribute to enhanced optical absorption in the semiconductor. Namely, (i) the PC back-reflector behaves as a perfect mirror (PM), exhibiting complete reflection over stop-gap frequencies; and (ii) the PC-semiconductor film interface coupl...

This paper describes the use of chemical cross-linking of ultrathin inorganic nanowires as a bottom-up strategy for nanostructure fabrication as well as a chemical detection platform. Nanowire microfibers are produced by spinning a nanowire dispersion into a cross-linker solution at room temperature. Nanomembranes with thicknesses down to 50 nm wer...

The electrical properties of inverse silicon opals (i-Si-o) was investigated with a focus on the effect of the photonic-crystal lattice constant, crystallinity, and hydrogen-plasma passivation of Si on the electrical conductivity of i-Si-o. The correlation between these material properties with the optical properties of i-Si-o was also examined. Th...

Schlanker mit Erfolg! Im Kolloidzustand stabile ultradünne Bi2S3-Nanodrähte (siehe Bild) mit ausgeprägten exzitonischen Eigenschaften, wie sie in Bismutchalkogeniden noch nie beobachtet wurden, und extrem hohen Extinktionskoeffizienten wurden in Gramm-Mengen synthetisiert. Nanostrukturen wie diese haben ein großes Potenzial für thermoelektrische An...

Currently, research is being directed towards thinning conventional 200–300µm thick silicon photovoltaic cells by an order of magnitude or more. The benefits of reducing the cell thickness include decreased material costs, enhanced cell flexibility, and reduced effects of light-induced degradation. However, one of the major challenges associated wi...

A study was conducted to demonstrate that the photoconductivity of a semiconductor film can be amplified by optically coupling it to a photonic crystal (PC) surface. Another objective of the study was to show that the photoconductivity enhancement attainable from surface resonant modes in thin films, coupled to PC surfaces was greater than the enha...