Thomas J. Macdonald

A TiO2 Nanofiber-Carbon Nanotube-Composite Photoanode for Improved Efficiency in Dye-Sensitized Solar Cells.

A light-scattering layer fabricated from electrospun titanium dioxide nanofibers (TiO2 -NFs) and single-walled carbon nanotubes (SWCNTs) formed a fiber-based photoanode. The nanocomposite scattering layer had a lawn-like structure and integration of carbon nanotubes into the NF photoanodes increased the power conversion efficiency from 2.9u2009% to 4.8u2009% under 1u2009Sun illumination. Under reduced light intensity (0.25u2009Sun), TiO2 -NF and TiO2 -NF/SWCNT-based DSSCs reached PCE values of up to 3.7u2009% and 6.6u2009%, respectively.

CuInS2/ZnS nanocrystals as sensitisers for NiO photocathodes

Nickel oxide (NiO) is the most universally studied photocathode to date, however, its poor fill factor (FF) makes its efficiency much lower than its counterpart, n-type photoanodes. Its significance in photovoltaics is based on the potential to fabricate tandem photoelectrodes in order to enhance the overall efficiency of the existing devices. Furthermore, limited work on the sensitisation of NiO with semiconducting nanocrystals (NCs) exists. For the first time, we have fabricated NiO photocathodes sensitised with aqueous CuInS2/ZnS NCs. The NCs were chemically bound to the NiO films with the aid of carboxyl and thiol groups. This was achieved without modifying the bulk surface properties of NiO. Binding of the NCs was investigated using TEM, SEM, XPS, XANES, EXAFS modelling and ToF-SIMS. NiO films were assembled into CuInS2/ZnS NC sensitised photocathodes and their photovoltaic properties were compared to those of unsensitised and dye-sensitised NiO solar cells. We demonstrate that non-toxic NCs can be used to sensitise NiO photocathodes to achieve an (almost) all-inorganic system.

A quantum dot sensitized catalytic porous silicon photocathode

Solar fuels have attracted considerable attention as an alternative energy vector in the context of the dwindling supplies of the planets non-renewable resources. The first step in solar fuel generation is often a photo-catalytic water splitting. Although a very large amount of work has been dedicated to optimise the photo-oxidation process (mostly based on titania), the development of highly efficient photocathodes is limited. In this paper, we report the fabrication and characterisation of a nano-structured photocathode using indium phosphide QDs and a bio-inspired Fe2S2(CO)6 catalyst, p-type porous silicon photocathode. Our hybrid electrode system produced a photocurrent density of −1.2 mA cm−2 with hydrogen evolution at low bias potentials.

Quantum Dot Sensitized Photoelectrodes

Quantum Dots (QDs) are promising alternatives to organic dyes as sensitisers for photocatalytic electrodes. This review article provides an overview of the current state of the art in this area. More specifically, different types of QDs with a special focus on heavy-metal free QDs and the methods for preparation and adsorption onto metal oxide electrodes (especially titania and zinc oxide) are discussed. Eventually, the key areas of necessary improvements are identified and assessed.

Photoresponsive properties of ultrathin silicon nanowires

Functional silicon nanowires (SiNWs) are promising building blocks in the design of highly sensitive photodetectors and bio-chemical sensors. We systematically investigate the photoresponse properties of ultrathin SiNWs (20u2009nm) fabricated using a size-reduction method based on e-beam lithography and tetramethylammonium hydroxide wet-etching. The high-quality SiNWs were able to detect light from the UV to the visible range with excellent sensitivity (∼1 pW/array), good time response, and high photoresponsivity (Ru2009∼u20092.5u2009×u2009104u2009A/W). Improvement of the ultrathin SiNWs photoresponse has been observed in comparison to 40u2009nm counter-part nanowires. These properties are attributable to the predominance surface-effect due to the high surface-to-volume ratio of ultrathin SiNWs. Long-term measurements at different temperatures in both the forward and reverse bias directions demonstrated the stability and reliability of the fabricated device. By sensitizing the fabricated SiNW arrays with cadmium telluride quantum d...

Porous silicon nanoparticles as a nanophotocathode for photoelectrochemical water splitting

The antireflective properties and nanometer sizes of silicon nanoparticles can be exploited for improved solar energy conversion. We report on using porous silicon nanoparticles as a photocathode for photoelectrochemical water splitting. An enhancement in the photocurrent density was observed when porous silicon nanoparticles were decorated with indium phosphide nanocrystals and a bio-inspired iron sulfur carbonyl electrocatalyst. Our system gave a photocurrent density of −2.2 μA cm−2 while generating hydrogen gas.

Cation exchange of aqueous CuInS2 quantum dots

Chalcopyrite copper indium disulfide (CIS) QDs have been of recent interest due to their non-toxicity. Although publications on CIS QDs are becoming more common, the majority of synthesis involves long chained insulating ligands, which are only soluble in non-polar solvents. Recent works have explored the tunable properties of CIS QDs by means of cation exchange with ZnS. Despite this, their tunable properties have been limited to use in organic solvents. This may be due to the cation exchange not being completely understood. For the first time, we present a controllable cation exchange for water soluble, tunable CIS QDs. We also show the partial exchange of indium for zinc, which is shown to provide these QDs with unique optical properties.

Photo-responsive Properties on Locally Confined Ultrathin Silicon Nanowires

Functional ultrathin silicon nanowires (SiNWs) are promising building blocks for high responsive photo-detectors and ultra-high sensitive bio-chemical sensors. In this work we investigate the photo responsive characteristics of of ultrathin SiNW arrays fabricated using a novel top-down process. The fabricated SiNW arrays were able to detect light from the UV to the visible range with good sensitivity and ultrahigh photoresponsivity (R~ 10 A/W). In addition, the SiNWs displayed good stability and reliability over long-term measurements at different temperatures (273 – 343 K) in both forward and reverse bias directions. By sensitizing the fabricated SiNW arrays with cadmium telluride (CdTe) quantum dots (QDs), hybrid QD SiNW arrays were created and displayed a significant improvement in photocurrent response under UV light, while preserving their performance in the visible light range. The fast, stable and high photo response of these new hybrid nanostructures is very promising towards the development of novel optoelectronic and photovoltaic devices.