David Worsley

A Transparent Conductive Adhesive Laminate Electrode for High‐Efficiency Organic‐Inorganic Lead Halide Perovskite Solar Cells

A self-adhesive laminate solar-cell electrode is presented based on a metal grid embedded in a polymer film (x-y conduction) and set in contact with the active layer using a pressure-sensitive adhesive containing a very low quantity (1.8%) of organic conductor, which self-organizes to provide z conduction to the grid. This ITO-free material performs in an identical fashion to evaporated gold in high-efficiency perovskite solar cells.

Efficient, Semitransparent Neutral-Colored Solar Cells Based on Microstructured Formamidinium Lead Trihalide Perovskite

Efficient, neutral-colored semitransparent solar cells are of commercial interest for incorporation into the windows and surfaces of buildings and automobiles. Here, we report on semitransparent perovskite solar cells that are both efficient and neutral-colored, even in full working devices. Using the microstructured architecture previously developed, we achieve higher efficiencies by replacing methylammonium lead iodide perovskite with formamidinium lead iodide. Current-voltage hysteresis is also much reduced. Furthermore, we apply a novel transparent cathode to the devices, enabling us to fabricate neutral-colored semitransparent full solar cells for the first time. Such devices demonstrate over 5% power conversion efficiency for average visible transparencies of almost 30%, retaining impressive color-neutrality. This makes these devices the best-performing single-junction neutral-colored semitransparent solar cells to date. These microstructured perovskite solar cells are shown to have a significant advantage over silicon solar cells in terms of performance at high incident angles of sunlight, making them ideal for building integration.

Latent Fingerprint Detection Using a Scanning Kelvin Microprobe

Electrochemical interactions between latent human fingerprints and metal surfaces in ambient air are investigated using a scanning Kelvin microprobe. Inorganic salts present in sweat deposited at fingerprint ridges locally depassivate the metal surface producing a Volta potential decrease of greater than 200 mV. Volta potential patterns may persist for months and prints may be visualized by potential mapping, even when overcoated with a polymer layer. Because the Volta potential differences are produced by involatile salts they persist when the organic components of the fingerprint residue have been volatilized by heating to 600 degrees C.

Kinetic and Mechanistic Studies of Rare Earth-Rich Protective Film Formation Using In Situ Ellipsometry

The deposition of rare earth metal (REM) rich (hydr)oxide films on pure iron and zinc surfaces has been studied using in situ ellipsometry. Iron and zinc surfaces freely corroding in near-neutral 0.86 mol dm(-3) aerated aqueous sodium chloride were found to be covered with 6-15 nm thick native (hydr)oxide films. The kinetics of REM-rich film growth for one redox active [Ce(III)] and two redox inactive [Y(III) and La(IU)] cations were measured. Addition of 2.5 x 10(-3) mol dm-3 REM chloride salts to the electrolyte resulted in rapid growth of REM-rich (hydr)oxide films on both metal substrates. Similar film growth rates were observed for each REM cation. REM-rich film deposition proceeds via the precipitation of REM hydroxides [M(OH)(3)] produced by cation hydrolysis proximal to the substrate-solution interface driven by increased interfacial pH resulting from cathodic oxygen reduction. When iron was cathodically polarized to near the free corrosion potential of zinc (-1.05 V vs. SCE) the pre-existing iron (hydr)oxide film was removed within 400 s and no deposition of REM-(hydr)oxide films was observed. On the basis of these findings it is proposed that REM-(hydr)oxide deposits only nucleate efficiently on the native (hydr)oxide covered metal surfaces

Novel environment friendly corrosion inhibitor pigments based on naturally occurring clay minerals

Novel, ceramic, corrosion inhibitor pigments consisting of cerium (III) and calcium (II) cation exchanged bentonites have been shown to provide effective cut-edge corrosion resistance in organic coated galvanised steel. The bentonite pigments were prepared from a naturally occurring (Wyoming) bentonite with a cation-exchange-capacity of 0.7 milli-equivalents per gram. Cation exchange was carried out by repeated washing with aqueous solutions of cerium (III) chloride and calcium (II) chloride to produce bentonites containing 31 500 ppm exchangeable cerium (III) and 13 500 ppm exchangeable calcium (II) respectively. The resulting bentonite pigments were dispersed in a polyester-resin based primer paint system to give a pigment volume concentration of 19%. For comparison, two similar primer systems were prepared containing a commercial calcium (II) exchanged silica pigment (Shieldex: 60 000 ppm calcium (II)) and a strontium chromate dispersion, both with a 19% pigment volume concentration. All three primer systems were applied (5 μm) to the zinc surface of galvanised 0.7 mm gauge sheet steel and overcoated with an architectural polyester topcoat (18 μm). The performance of the inhibitor pigments was compared by measuring the rate of corrosion-driven organic coating delamination from the cut edge of samples during 1000 h of salt-spray testing. The calcium (II) bentonite pigment exhibited an anti-delamination performance similar to that of strontium chromate but superior to that of Shieldex. However, the cerium (III) bentonite pigment was superior in performance to both strontium chromate and Shieldex. Thus, the bentonite pigments represent promising, environmentally friendly, ion-exchange corrosion inhibitors which exhibit good anti-delamination performance by comparison with current commercial systems. Neue umweltfreundliche Korrosionsinhibitorpigmente auf Basis naturlich vorkommender Tonmineralien Es hat sich gezeigt, dass neue, keramische Korrosionsinhibitorpigmente, die aus Cer(III) und Kalzium(II) Kationen-ausgetauschten Bentoniten bestehen, einen wirksamen Korrosionsschutz an Schnittkanten von organisch beschichtetem, verzinkten Stahl bieten. Die Bentonitpigmente wurden aus einem naturlich vorkommenden (Wyoming) Bentonit mit einer Kationen-Austauschkapazitat von 0,7 Milliaquivalenten pro Gramm hergestellt. Der Kationenaustausch wurde durch wiederholtes Waschen mit wassrigen Losungen aus Cer(III)chlorid und Kalzium(II)chlorid durchgefuhrt, um Bentonite mit 31 5000 ppm austauschbarem Cer(III) bzw. 13 5000 ppm austauschbarem Kalzium(II) herzustellen. Die sich daraus ergebenden Bentonitpigmente wurde in einem auf Polyesterharz basierenden Grundbeschichtungssystem feinverteilt, so dass sich eine Pigmentvolumenkonzentration von 19% ergab. Zum Vergleich wurden zwei ahnliche Grundbeschichtungssysteme hergestellt, die ein handelsubliches Kalzium(II) ausgetauschtes Silikapigment (Shieldex: 60 000 ppm Kalzium(II)) und eine Strontiumchromatdispersion, beide mit einer Pigmentvolumenkonzentration von 19%, enthielten. Alle drei Grundbeschichtungssysteme wurden auf die Zinkoberflache eines verzinkten 0,7 mm dicken Stahlbleches aufgebracht (5 μm) und mit einer Polyester Deckbeschichtung (18 μm) uberschichtet. Das Verhalten der Inhibitorpigmente wurde durch Messung der durch Korrosion ausgelosten Enthaftung der organischen Beschichtung von den Schnittkanten der Proben wahrend 1000 h Salzspruhnebelprufung verglichen. Das Kalzium(II)-Bentonitpigment zeigte ein Anti-Enthaftungsverhalten, das dem des Strontiumchromats vergleichbar aber besser als das des Shieldex war. Das Cer(III)-Bentonitpigment war in seinem Verhalten jedoch sowohl dem Strontiumchromat als auch dem Shieldex uberlegen. Das bedeutet, dass die Bentonitpigmente vielversprechende, umweltfreundliche, Ionen-ausgetauschte Korrosionsinhibitoren darstellen, die im Vergleich mit handelsublichen Systemen ein gutes Anti-Enthaftungsverhalten zeigen.

Polyaniline Inhibition of Corrosion-Driven Organic Coating Cathodic Delamination on Iron

The polyaniline emeraldine salt of paratoluenesulfonic acid (PAni-pTS) is dispersed in polyvinylbutyral coatings adherent to an iron surface. Such dispersions are shown to effectively inhibit corrosion-driven coating delamination (cathodic disbondment) when 5% w/v (0.86 M) aqueous chloride electrolyte contacts a penetrative coating defect. A scanning Kelvin probe is used to quantify the influence of PAni-pTS volume fraction (Φ p a ) on delamination rate and the potential of the intact (undelaminated) coated surface (E i n t a c t ). Secondary ion mass spectroscopy and atomic force microscopy are used to determine the time-dependent thickness of an oxide layer developing at the coating-iron interface. At 20°C, high relative humidity (93%), and Φ p a = 0.3, the iron oxide layer grows at a constant rate of 5.6 X 10 - 3 nm s - 1 . E i n t a c t increases monotonically from 0.2 to 0.56 V vs. SHE, and coating delamination rates decrease by ca. 95% as Φ p a is increased from 0 to 0.25. Addition of 0.01 M Na-pTS to the experimental electrolyte has no effect. An inhibition mechanism is proposed in which through-coating cathodic O 2 reduction is suppressed by the ennoblement of substrate potentials and the OH - product of O 2 reduction is absorbed through PAni-pTS mediated pH buffering.

Highly efficient, flexible, indium-free perovskite solar cells employing metallic substrates

Flexible perovskite solar cells with power conversion efficiencies of up to 10.3% have been prepared using titanium foil as an electrode substrate. Our method uses an indium-free transparent counter electrode which allows device performance to remain high despite repeated bending, making it suitable for roll-to-roll processing.

Use of the Scanning Reference Electrode Technique for the Evaluation of Environmentally Friendly, Nonchromate Corrosion Inhibitors

Abstract The scanning reference electrode technique (SRET) has been used to study the influence of a range of anodic and cathodic corrosion inhibitors on patterns of localized corrosion occurring o...

Perovskite processing for photovoltaics: a spectro-thermal evaluation

Thermal analysis (TGA and DSC), coupled with evolved gas FTIR spectroscopy, has been used to study the changes occurring during, and differences between materials after, the annealing step of mixed-halide methylammonium lead halide perovskites. This is important because, to date, the material is the most efficient light harvester in highly efficient, 3rd generation perovskite photovoltaic devices, and processing plays a significant role in device performance. TGA-FTIR data show only solvent evolution during the annealing step, whilst post-annealing analysis shows that the resulting material still contains a significant amount of residual solvent; however, efficient DMF removal was possible using a silica gel desiccant for a period of 3 days. The data also show that methylammonium halide decomposition does not occur until temperatures well above those used for perovskite processing, suggesting that this is not a significant issue for device manufacture. The absence of a well-defined, reversible tetragonal – cubic phase change around 55 °C in the DSC data of the annealed material, and the presence of HCl in evolved gas analysed following thermal decomposition, demonstrates that CH3NH3I3−xClx does retain some Cl after annealing and does not simply form stoichiometric CH3NH3PbI3 as has been suggested by some workers.

Photomineralization of salicylic acid: a kinetic study

Abstract The kinetics of the photomineralization of salicylic acid (SA) sensitized by Degussa P25 titanium dioxide (TiO 2 ) dispersions in oxygenated aqueous solution are reported as a function of the following experimental parameters: [TiO 2 ], percentage of O 2 , [SA], temperature ( T ) and light ( I ). The kinetics of SA photomineralization conform to a Langmuir—Hinshelwood kinetic scheme with SA and O 2 adsorbed at different sites with apparent Langmuir adsorption coefficients of (6.1±1.2)×10 4 mol −1 dm 3 and 0.061±0.007 kPa −1 respectively. The overall activation energy for the system was determined as 4.6±0.2 kJ mol −1 . Two major stable reaction intermediates are identified (dihydroxybenzoic acids (DHBA) and catechol (C)) and the excistence of a further pathway involving one or more very unstable and, as yet, unidentified reaction intermediates is proposed. A kinetic model is presented which describes the temporal behaviour of the concentrations of SA, CO 2 and the major photogenerated intermediates (DHBA and C). This model is used to predict successfully the temporal behaviour of the major intermediates in the photomineralization of SA under non-standard conditions.