We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

The morphology, structure, and optical properties of gallium nitride (GaN) nanowires grown using metal-organic chemical vapor deposition (MOCVD) on r-plane sapphire using gold and nickel seed particles were investigated. We found that different seed particles result in different growth rates and densities of structural defects in MOCVD-grown GaN nanowires. Ni-seeded GaN nanowires grow faster than Au-seeded ones, and they do not contain the basal plane stacking faults that are observed in Au-seeded GaN nanowires. We propose that stacking fault formation is related to the supersaturation and surface energies in different types of seed particles. Room temperature photoluminescence studies revealed a blue-shifted peak in Au-seeded GaN nanowires compared to the GaN near-bandgap emission. The blue-shifted peak evolves as a function of the growth time and originates from the nanowire base, likely due to strain and Al diffusion from the substrate. Our results demonstrate that seed particle composition has a direct impact on the growth, structure, and optical properties of GaN nanowires and reveal some general requirements for seed particle selection for the growth of compound semiconductor nanowires.

The growth mechanism of epitaxial GaN nanowires grown using particle-mediated chemical vapour deposition was investigated. By examining the diameter-dependent growth rate of GaN nanowires, we show that the kinetic reaction-limited growth of GaN nanowires originates from the combination of mono-nuclear and poly-nuclear growth rather than the Gibbs-Thompson effect. We present a generalized nucleation-mediated growth model to describe the diameter dependence of the nanowire growth rate and show that the nucleation of sources occurs at the vapour/liquid/solid three-phase boundary. From the same model, we demonstrate that increased hydrogen concentration in the carrier gas reduces the supersaturation, leading to a reduced GaN nanowire growth rate. Our approach can be applied to other nanowire materials systems, and it allows the determination of the preferred nucleation site during nanowire growth.

Self-seeded growth of semiconducting nanowires offers significant advantages over foreign metal-seeded growth by eliminating seed-associated impurities. However, density and diameter control of self-seeded nanowires has proven challenging although it is required for integration of nanowires into optoelectronic devices. We report the selfseeded growth of GaAs nanowire arrays on GaAs (111)B, (110), and (111)A substrates by metal−organic chemical vapor deposition. Our approach involves two steps: the in situ deposition of Ga seed particles and subsequent GaAs nanowire growth. Control of nanowire diameter and array density is achieved via Ga seed deposition temperature and substrate orientation; increased seed deposition temperatures or changing substrate orientation from (111)A to ( 110) and ( 111)B yields reduced areal density and larger nanowire diameters. The density and diameter control approaches could be extended to other self-seeded III−V nanowire material systems.

Despite extensive research in photocatalytic water splitting, electrolyte usage varies greatly across different photocells. Photocatalytic water splitting continues to be performed in a wide range of electrolytes, from very acidic to very basic, with incomplete understanding of how the electrolyte composition affects performance. This study provides guidelines for electrolyte selection in water splitting applications. To determine properties that comprise an ideal electrolyte for photocatalytic electrolysis, the effects of several parameters were studied: pH, dissolved oxygen, conductivity, and composition. The photoactive anode was a nanostructured thin TinormalO2 film synthesized by a flame aerosol process. The photocatalytic conversion efficiency increased with both pH and conductivity, but changes in dissolved oxygen levels had no discernible effect. The electrolyte composition was adjusted using selected salts and bases. Although the effect of the cation was negligible, anions were found to reduce efficiencies if their oxidation potential makes them thermodynamically favored over water molecules for oxidation. The results of these studies were applied in an analysis of the prospects for splitting seawater to produce hydrogen.