Aurelien Du Pasquier

Conducting and transparent single-wall carbon nanotube electrodes for polymer-fullerene solar cells

We describe the use of single-wall carbon nanotube (SWNT) thin films as transparent and conducting electrodes for hole collection in poly(hexyl)thiophene-[6-6]phenyl-C61-butyric acid methyl ester (P3HT-PCBM) organic photovoltaics. We report a power conversion efficiency of 1%, with a fill factor of 0.3 and a short-circuit current of 6.5mA∕cm2 under 100mW∕cm2 polychromatic white light illumination measured in air. These values are comparatively higher than reference cells of similar thickness made on indium tin oxide (ITO) glass substrates. This is attributed to the three-dimensional nature of the interface between the SWNTs and the P3HT-PCBM nanocomposite. Our results indicate that solution processed SWNT thin films are a viable alternative to ITO for photovoltaic devices, eliminating an expensive vacuum deposition step in the fabrication of organic solar cells.

Dye sensitized solar cells using well-aligned zinc oxide nanotip arrays

Well-aligned zinc oxide (ZnO) nanotip arrays were grown on fluorinated tin oxide coated glass using metal organic chemical vapor deposition. Dye (N719) sensitized photoelectrochemical cells comprising of ZnO nanotip arrays were fabricated and characterized. It is found that the power conversion efficiency of the cells increases with the length of the ZnO nanotips. The cells with 3.2μm ZnO nanotip array exhibited an incident photon-to-current conversion efficiency of 21.1% (at 550nm) and a power conversion efficiency of 0.55% under 1 sun irradiance. Light harvesting in ZnO nanotips also contributes to the photocurrent in the UV range.

A Nonaqueous Asymmetric Hybrid Li4Ti5 O 12 / Poly(fluorophenylthiophene) Energy Storage Device

An asymmetric hybrid energy storage device has been built using a lithium titanate intercalation anode and the pseudocapacitive electronically conducting polymer poly(fluorophenythiophene). Results show that the device operates in the power range of electrochemical double-layer capacitors, while having three to four times their energy density, and a voltage profile and self-discharge characteristics typical of a battery. The cycle life is also intermediate between that of a battery and a supercapacitor, in the range of several thousands of cycles.

Dye-sensitized solar cells using ZnO nanotips and Ga-doped ZnO films

Ga-doped ZnO (GZO) transparent conducting films and well-aligned ZnO nanotips were sequentially grown on a glass substrate using metal–organic chemical vapor deposition (MOCVD). The morphology control of ZnO from dense films to nanotips was realized through temperature-modulated growth. The ZnO nanotips/GZO structure was sensitized with dye N719 to form photoelectrochemical cells. It is found that the power conversion efficiency linearly increases with the length of ZnO nanotips. For the 1.0 cm2 dye-sensitized solar cell built from 4.8 µm ZnO nanotips, a peak incident photo-to-current conversion efficiency of 79% (at ~530 nm) and a power conversion efficiency of 0.77% under the illumination of one sun-simulated sunlight were achieved. UV light harvesting directly by ZnO was observed. The I–V characteristics of the cells were analyzed using a one-diode equivalent circuit model.

Photoinduced charge transfer between poly"3-hexylthiophene… and germanium nanowires

Germanium nanowires (GeNWs) were used to enhance the properties of organic photovoltaic devices. GeNWs were grown to a length of 1–5μm on SiO2 by the vapor-liquid-solid method catalyzed by 20nm Au seeds. Once grown, the GeNWs were dispersed in solution with poly(3-hexylthiophene) and spin cast into films. The photoluminescence and external quantum efficiency of the films indicated a significant increase in exciton dissociation and photocurrent generation. The results imply that the GeNWs may act as an electron acceptor for bulk heterojunction hybrid-inorganic/organic photovoltaic devices. The impacts of GeNW on device characteristics are discussed.

Self-Assembled TiO2 with Increased Photoelectron Production, and Improved Conduction and Transfer: Enhancing Photovoltaic Performance of Dye-Sensitized Solar Cells

Highly crystalline mesoporous anatase TiO(2) is prepared through supramolecular self-assembly and by utilizing cetyltrimethylammonium bromide (CTAB) as templating material. Photoanodes of dye-sensitized solar cells (DSSCs) made from these TiO(2) nanoparticles are found to have a high specific surface area of 153 m(2)/g and high surface roughness. Optical absorption spectroscopy studies reveal that the photoanode films adsorb four times more dye than films made of commercial P25 TiO(2). Mercury porosimetry and field emission scanning electron microscope (FESEM) studies show hierarchical macro- and meso-porosity of the photoanode films leading to better dye and electrolyte percolation, combined with improved electron conduction pathways compared to P25 films. Electrochemical impedance studies confirm lower impedance and higher electron lifetime in the synthesized mesoporous TiO(2) films compared to P25 films. Higher photovoltaic efficiency was recorded of cells made from the synthesized mesoporous TiO(2) in comparison to the corresponding cells made from P25. Incident-photon-to-current efficiency data provided critical understanding of recombination kinetics, and provided proof of Mie scattering by the self-assembled submicrometer sized TiO(2) aggregates and the macropores in their structure. The scattering phenomenon was further corroborated by diffused reflectance studies. An in-depth analysis of CTAB-templated mesoporous TiO(2) has been conducted to show how it can be a good candidate photoanode material for enhancing the performance of DSSCs.

Plasticized conjugated polymers: a possible route to higher voltage solar cells

The introduction of propylene carbonate (PC) into the poly (3-alkyl)thiophenes (P3AT) poly(octyl)thiophene (P3OT) and poly(hexyl)thiophene) (P3HT) is studied. In both cases, we observe a diminution of their melting temperature, which demonstrates a plasticizing effect. We also observe an increase of photovoltage and photocurrent in sandwich devices M//P3AT+PC//ITO-PET where M=Al, Mg and ITO-PET is Indium thin oxide coated on polyester. We attribute this effect to the introduction of oxygen from the PC. When mixed with an electron acceptor PCBM, the photocurrents only slightly increase and the photovoltages are similar. In this case, the presence of oxygen is detrimental to the system.