David Galipeau

Electrospun carbon nanofibers as low-cost counter electrode for dye-sensitized solar cells.

Electrospun carbon nanofibers (ECNs) have been explored as an electrocatalyst and low-cost alternative to platinum (Pt) for triiodide reduction in dye-sensitized solar cells (DSCs). The results of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements indicated that the ECN counter electrodes exhibited low charge-transfer resistance (Rct), large capacitance (C), and fast reaction rates for triiodide reduction. Although the efficiency (η) of ECN-based cells was slightly lower than that of Pt-based cells, their short circuit current density (Jsc) and open circuit voltage (Voc) were comparable. The ECN-based cells achieved an energy conversion efficiency (η) of 5.5 % under the AM 1.5 illumination at 100 mW cm(-2). The reason for lower cell performance using the ECN electrode was because of its lower fill factor (FF) than that of Pt-based cells, probably caused by high total series resistance (RStot) at ∼15.5 Ω cm2, which was larger than that of ∼4.8 Ω cm2 in the Pt-based devices. Simulated results showed that the fill factor (FF) and η could be substantially improved by decreasing RStot, which might be achieved by using thinner and highly porous ECNs to reduce the thickness of the ECNs counter electrode.

Dye-sensitized solar cells based on low cost nanoscale carbon/TiO2 composite counter electrode

A dye-sensitized solar cell based on low cost nanoscale carbon/TiO2 composite counter electrode was fabricated and its photovoltaic performance (η = 5.5%, AM 1.5, 91.5 mW cm−2) was comparable to that from platinum counter-electrode devices (η = 6.4%, AM 1.5, 91.5 mW cm−2) made at similar conditions.

Composite of TiO2 nanofibers and nanoparticles for dye-sensitized solar cells with significantly improved efficiency

A composite made of electrospun TiO2 nanofibers and conventional TiO2 nanoparticles is an innovative type of photoanode, which noticeably improves the harvesting of light without substantially sacrificing the attachment (uptake) of dye molecules for convenient fabrication of dye-sensitized solar cells with significantly improved efficiency.

A review of polymer multijunction solar cells

Polymer solar cells are one of the most promising prospects for widespread renewable energy due to their low cost, light weight, and mechanical flexibility. However, to date, low efficiencies (7.9%) of these devices inhibit their application. New materials and device designs are needed to increase the efficiency and make this technology available for large-scale applications. A polymer multijunction solar cell made of two or more subcells in series, parallel, or other special connections offers a potential solution to the losses in the current polymer single-junction solar cells. In this article, the recent developments in polymer multijunction photovoltaic materials, cell structures, and device modelling are reviewed. In addition, the current challenges that need to be addressed to achieve siginificantly higher efficiency are discussed.

Development of a micromachined hazardous gas sensor array

AbstractThe objective of this work was to develop a micro-hotplate-based gas sensor array for detecting ammonia (NH 3 ), hydrogen sulfide (H 2 S),and methane (CH 4 ) gases. Sensing film fabrication parameters were studied with micro-hotplates based on resistive temperature detectors andmicroelectro-mechanical system (MEMS) micro-hotplate arrays. SnO 2 /Pt, WO 3 /Au, and ZnO sensing films were found sensitive to thetarget gases NH 3 ,H 2 S, and CH 4 , respectively, but had some cross-sensitivity. Other limitations of the sensing films were baseline drift, highresistance, and recovery time. Sensor array responses to the gases were unique, which should allow selectivity to be obtained by patternrecognition.# 2003 Elsevier Science B.V. All rights reserved. Keywords: Micromachined gas sensor; Hazardous gas sensor; Gas sensor array; MEMS gas sensor 1. IntroductionAgriculture has a strong need for improved gas sensors,especially in animal confinement facilities, where hazardousgases such as hydrogen sulfide (H

A study of low-cost sensors for measuring low relative humidity

Abstract The performance of low-cost commercially available polymeric humidity sensors has been compared to that of prototype thick- and thin-film polymer-based sensors that will be optimized for improved performance at low relative humidity (RH). The commercially available humidity sensors examined include polymeric capacitive and resistive types. The prototype sensors utilize both thick- and thin-film interdigitated electrodes, on quartz and ceramic substrates, with polyimide sensing films. Both capacitive and surface acoustic wave (SAW) sensing mechanisms have been studied for the thin-film structure. The commercial capacitive microsensors have a linear response in the range 5–95% RH. The resistive sensors are non linear, but the signal-conditioning circuit can be modified for improved sensitivity in a particular RH range. The prototype thick-film sensor has a non-linear response, while the response of the thin-film prototype sensor is comparable to that of the commercial capacitive microsensors. The SAW sensor has the potential for higher sensitivity than the commercial capacitive microsensors, but is less linear.

Improved dew point measurements based on a SAW sensor

Abstract Optical dew point hygrometers have several drawbacks including high cost, frequent mirror contamination, instability under continuous use, and inability to detect the frost-point transition. In this work a novel hybrid sensor, and a surface acoustic wave (SAW) oscillator were used to compare optical and SAW dew point measurement techniques in the areas of condensation sensitivity, surface contamination effects, frost point transition behavior and dew point measurement resolution. The SAW technique was found to better control condensation density than the optical technique, allowing for a resolution of 0.03°C versus 0.2°C for a commercial optical dew point hygrometer. The SAW technique was also found to be much less susceptible than the optical technique to surface contamination. The frost point transition was found to cause significant measurement instability when controlling condensation density with SAW velocity or optical reflection voltage while SAW amplitude provided stable measurements. A Teflon Al coating provided accurate SAW dew point measurements at extremely low condensation densities, which may allow for improved measurements at very low relative humidities.

Mixed (porphyrinato)(phthalocyaninato) rare-earth(III) double-decker complexes for broadband light harvesting organic solar cells

Solution-processed organic-inorganic hybrid bulk heterojunction solar cells with the capability of broadband solar photon harvesting over the ultraviolet-visible-near-infrared spectral range are developed. A series of mixed (porphyrinato)(phthalocyaninato) rare-earth double-decker complexes, [MIIIH(TClPP){Pc(α-OC4H9)8}] (1–7; M = Y, Sm, Eu, Tb, Dy, Ho, Lu; TClPP = meso-tetrakis(4-chlorophenyl)porphyrinate; Pc(α-OC4H9)8 = 1,4,8,11,15,18,22,25-octakis(1-butyloxy)phthalocyaninate) and [YIII(TClPP)(Pc)] (8, Pc = unsubstituted phthalocyaninate), along with a heteroleptic bis(phthalocyaninato) yttrium double-decker complex [YIIIH(Pc){Pc(α-OC4H9)8}] (9), are synthesized and utilized as broadband absorbers and electron donors (D), whereas N,N′-bis(1-ethylhexyl)-3,4:9,10-perylenebis(dicarbox-imide) (PDI) or [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) is adopted as primary electron acceptor (A1). For suppressing the fatal back charge transfer at D/A1 interface, the D:A1 blend is fabricated within an in situ formed cheap inorganic network of nanoporous TiOx, which can act as a secondary electron acceptor (A2). For characterization of these structures, steady state spectroscopy, fluorescence dynamics, atomic force microscopy, current–voltage characteristics, and photoelectrical properties of the active materials or devices are investigated. Solar cells utilizing PDI as the primary acceptor show higher values in open circuit voltage, fill factor, and power conversion efficiency over those cells using PCBM as the primary acceptor. With a cell area of 0.36 cm2, good efficiencies of up to 0.82% are achieved by the aforementioned double-decker complex:PDI:TiOx blends under 1-sun air mass 1.5 global illumination. These results conclude that double-decker bis(tetrapyrrole) complexes are promising photovoltaic materials with tunable absorption and photophysical properties.

Characterization of SiO2 surface treatments using AFM, contact angles and a novel dewpoint technique

Abstract The properties of sensing surfaces are particularly important in chemical and biosensing since they affect the adhesion of sensing films and the sorption of analyte molecules onto the active area of the sensor. The objectives of this work were to study the effects of several surface treatments on glass and quartz using atomic force microscopy, contact angle measurements, and a novel dewpoint error technique, in order to develop a better understanding of the effects of these treatments. The dewpoint error technique was also examined as a novel method for measuring surface energy that may have advantages over contact angle measurements. Most significantly, chromic acid and oxygen/argon sputtering treatments were found to substantially decrease the contact angles of both glass and quartz. The surface roughness of glass was markedly increased by acetic acid, heated NaOH, and piranha etch while HCl and KOH caused the highest surface roughness for quartz. A reasonably good correlation was found between decreasing contact angles and increasing dewpoint error, suggesting that the dewpoint technique may provide a quantitative measure of surface energy without some of the drawbacks of contact angle measurements. There was no correlation found between surface roughness and contact angle hysteresis or dewpoint error.

Organic photovoltaic cells made from sandwich-type rare earth phthalocyaninato double and triple deckers

This work presents organic-inorganic hybrid solar cells, which possess the capability for broad band photon harvesting from an ultraviolet-visible to a near infrared range. These solar cells are bulk heterojunction devices, which have been fabricated by free base phthalocyanine and rare earth phthalocyaninato double or triple deckers (electron donors) with a perylenediimide derivative (electron acceptor). Two-type cell structures with or without nanostructured TiO2 layers have been presented. A characterization of the structures, steady state spectroscopy, fluorescence dynamics, and photoelectrical property of these cells and the active materials has been carried out. A cell structure of In2O3:SnO2∕TiO2-active material-TiO2∕Al has shown a significant improvement in conversion efficiency.