Rudresh Ghosh

Nanoforest Nb2O5 Photoanodes for Dye-Sensitized Solar Cells by Pulsed Laser Deposition

Vertically aligned bundles of Nb(2)O(5) nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye-sensitized solar cells (DSSC). They were characterized using scanning and transmission electron microscopies, optical absorption spectroscopy (UV-vis), and incident-photon-to-current efficiency (IPCE) experiments. The background gas composition and the thickness of the films were varied to determine the influence of those parameters in the photoanode behavior. An optimal background pressure of oxygen during deposition was found to produce a photoanode structure that both achieves high dye loading and enhanced photoelectrochemical performance. For optimal structures, IPCE values up to 40% and APCE values around 90% were obtained with the N(3) dye and I(3)(-)/I(-) couple in acetonitrile with open circuit voltage of 0.71 V and 2.41% power conversion efficiency.

Electric-field-driven phase transition in vanadium dioxide

We report on local probe measurements of current-voltage and electrostatic force-voltage characteristics of electric-field-induced insulator to metal transition in VO2 thin film. In conducting AFM mode, switching from the insulating to metallic state occurs for electric-field threshold E~6.5\times10^7 Vm-1 at 300K. Upon lifting the tip above the sample surface, we find that the transition can also be observed through a change in electrostatic force and in tunneling current. In this noncontact regime, the transition is characterized by random telegraphic noise. These results show that electric field alone is sufficient to induce the transition; however, the electronic current provides a positive feedback effect that amplifies the phenomena.

Surface Patterning of Mesoporous Niobium Oxide Films for Solar Energy Conversion

An array of periodic surface features were patterned on mesoporous niobium oxide films by a soft-lithographic technique with the goal of constructing a photonic crystal (PC) structure on the back side of the oxide. The oxide films, fabricated by mixing sol-gel derived niobium oxide nanoparticles and hydroxypropyl cellulose, were employed as photoelectrodes in dye-sensitized solar cells (DSSCs), and their performance evaluated against their flat counterparts. The surface patterns were imprinted using a photocurable perfluoropolyether (PFPE) soft-replica of a silicon master with a two-dimensional array of cylindrical posts (200 nm (D) × 200 nm (H)) in hexagonal geometry. The PC on the niobium oxide surface caused large changes in optical measurements, particularly in the blue wavelengths. To evaluate the optical effect on solar energy conversion, the incident photon-to-current conversion efficiency (IPCE) was measured in the patterned devices and the control group. The IPCE of patterned niobium oxide anodes exhibited a relative enhancement in photocurrent generation over the wavelength range corresponding to the higher absorption in optical measurements.

Controlled seeding of laser deposited Ta:TiO2 nanobrushes and their performance as photoanode for dye sensitized solar cells.

Hexagonal patterned indium tin oxide (ITO) with a height of 1.5 μm was fabricated on fluorinated SnO2 (FTO) substrate via nanoimprint lithography and pulsed laser deposition (PLD). Tantalum doped TiO2 was deposited on the patterned substrate by PLD. The film of Ta:TiO2 grew vertically and separately on the patterned ITO and formed a brush-like structure. Dye-sensitized solar cells with the Ta:TiO2 film deposited on the patterned substrate as well as flat FTO substrate for comparison were fabricated and tested. The device with the patterned substrate showed a 25% increase in short circuit current (Jsc) compared to the one with flat FTO substrate. Optical and photoelectrochemical characterization techniques were performed to investigate the improvement. The increase of Jsc was attributed to the enhancements of light absorption in the 600-750 nm range and collection of excited electrons by the brush-like structure and the patterned ITO, respectively.

Efficient high surface area vertically aligned metal oxide nanostructures for dye-sensitized photoanodes by pulsed laser deposition

Vertically aligned bundles of TiO2 nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye sensitized solar cells (DSSC) using scanning electron microscopy (SEM), light absorption spectroscopy (UV-Vis), and incident photon-to-current efficiency (IPCE) experiments. An optimal background pressure of oxygen during deposition was discovered to produce a photoanode structure that simultaneously achieves high surface area and improves charge transport for enhanced photoelectrochemical performance. UV-Vis studies show that there is a 1.4x enhancement of surface area for PLD-TiO2 photoanodes compared to the best sol-gel films. PLD-TiO2 DSSC IPCE values are comparable to 3x thicker sol-gel films and nearly 92% APCE values have been observed for optimized structures.

Corrigendum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level

Corrigendum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level

Erratum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level (Nature Communications (2015) 6 (7482) DOI:10.1038/ncomms8482)

Corrigendum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level

Erratum: Corrigendum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level

Corrigendum: Revealing the planar chemistry of two-dimensional heterostructures at the atomic level