Barney E. Taylor

Fabrication of Highly-Ordered TiO2 Nanotube Arrays and Their Use in Dye-Sensitized Solar Cells

Highly ordered TiO(2) nanotubes were successfully fabricated using a nanoporous alumina templating method. A modified sol-gel route was used to infiltrate the alumina pores with Ti(OC(3)H(7))(4) which was subsequently converted into TiO(2) nanotubes. The average external diameter, tube lengths, and wall thickness achieved were 295 nm, 6-15 microm, and 21-42 nm, respectively. Diffraction data reveals that the nanotubes consist solely of the anatase phase. Dye-sensitized solar cells using TiO(2) nanotube arrays as the working electrode yielded power conversion efficiencies as high as 3.5% with a maximum incident photon-to-current conversion efficiency of 20% at 520 nm.

Investigation of electrostatic self-assembly as a means to fabricate and interfacially modify polymer-based photovoltaic devices

This work focuses on studying a water-based processing method for fabricating and modifying polymer-based photovoltaic devices based on donor–acceptor type complexes. Electrostatic self-assembly is a simple technique that involves immersion of a substrate into dilute aqueous solutions of positively and negatively charged polymers. Extremely thin layers of these polymers are adsorbed onto the surface and their structure can be tailored by manipulating deposition conditions such as the concentration, pH, and salt content. Poly(p-phenylene vinylene) (PPV) containing bilayers were examined as the donor block and water soluble, functionalized C60 molecules were investigated for the acceptor block. By varying the number of bilayers deposited in each individual block (i.e., the block thickness), we have been able to demonstrate a peak in device performance. By controlling the thickness of both the donor and acceptor blocks, we have determined the optimal device architecture for this system. Additionally, we have...

Electrostatic self-assembly as a means to create organic photovoltaic devices

Abstract Recently, there has been a significant amount of work done on making photovoltaic devices (solar cells) from thin films of conjugated polymers and other organic systems. The advantages over conventional inorganic systems include the potential to create lightweight, flexible, and inexpensive structures. The challenge, however, has been to create more highly efficient devices. To date, the primary photovoltaic device mechanism that has been utilized is that of photoinduced charge transfer between an electron donor and acceptor. In this study, similar photovoltaic devices are fabricated using a water-based electrostatic self-assembly procedure, as opposed to the more conventional spin-coating and/or vacuum evaporation techniques. In this process, layers of oppositely charged species are sequentially adsorbed onto a substrate from an aqueous solution and a film is built up due to the electrostatic attraction between the layers. The technique affords molecular level control over the architecture and gives bilayer thickness values of the order of tens of angstroms. By repeating this process a desired number of times and utilizing different cations and anions, complex architectures can be created with very accurate control over the thickness and the interfaces. We have examined a number of systems built from a variety of components including a cationic PPV precursor, functionalized C 60 , and numerous other polyelectrolytes. We report on the device characteristics of these films and on the overall applicability of this technique to the fabrication of photovoltaic devices.

Photovoltaic interface modification via electrostatic self-assembly

The device efficiency of PPV-C 60 based photovoltaic devices has been substantially increased by increasing the interfacial area between the electron donor and acceptor layers. Electrostatic Self-Assembly (ESA) provides a means to deposit thin films of electroactive materials with a very controlled thickness and has shown usefulness in modifying physical and electrical interfaces. In this study, we attempt to control the effective interfacial area by modifying the interface between the PPV electron donor and C 60 -based electron acceptor with molecularly blended ESA bilayers of PPV and derivatized C 60 . It is observed that with only 2 bilayers of (PPV/C 60 - ) a 3-fold increase in device efficiency is obtained. Thus, ESA films offer promise for the nanoscaled modification of interfaces in organic-based photocells.

Space-radiation-induced effects in polymer photodetectors

Self-assembled polymer photo-detectors (PPDs) composed of ruthenium complex N3 and PPDs based on thin films of poly(p-phenylene vinlyene) with sulfonated polystyrene are examined for their ability to function in a simulated space radiation environment. Examination of the PPD pre- and post- response data following gamma-ray irradiation ranging in total dose from 10 krad(Si) to 100 krad(Si) are examined. The output photovoltage was observed to decrease for all irradiated devices. The brief study was performed at room temperature and a discussion of the preliminary data and results are presented.