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Investigation into Photoconductivity in Single CNF/TiO(2)-Dye Core-Shell Nanowire Devices.

Li Z, Rochford C, Javier Baca F, Liu J, Li J, Wu J - Nanoscale Res Lett (2010)

Bottom Line: A vertically aligned carbon nanofiber array coated with anatase TiO(2) (CNF/TiO(2)) is an attractive possible replacement for the sintered TiO(2) nanoparticle network in the original dye-sensitized solar cell (DSSC) design due to the potential for improved charge transport and reduced charge recombination.Although the reported efficiency of 1.1% in these modified DSSC's is encouraging, the limiting factors must be identified before a higher efficiency can be obtained.This work employs a single nanowire approach to investigate the charge transport in individual CNF/TiO(2) core-shell nanowires with adsorbed N719 dye molecules in dark and under illumination.

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ABSTRACT
A vertically aligned carbon nanofiber array coated with anatase TiO(2) (CNF/TiO(2)) is an attractive possible replacement for the sintered TiO(2) nanoparticle network in the original dye-sensitized solar cell (DSSC) design due to the potential for improved charge transport and reduced charge recombination. Although the reported efficiency of 1.1% in these modified DSSC's is encouraging, the limiting factors must be identified before a higher efficiency can be obtained. This work employs a single nanowire approach to investigate the charge transport in individual CNF/TiO(2) core-shell nanowires with adsorbed N719 dye molecules in dark and under illumination. The results shed light on the role of charge traps and dye adsorption on the (photo) conductivity of nanocrystalline TiO(2) CNF's as related to dye-sensitized solar cell performance.

No MeSH data available.


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a Schematic diagram of a single CNF/TiO2 core–shell NW device. b SEM image of a device used in the study. Inset shows a four-probe device used to measure contact resistance and resistivity. c TEM image showing the core–shell structure of the CNF/TiO2 NW. The yellow dashed line shows the interface between the TiO2 shell and CNF core. d Microstructure of the core–shell NW, insets give the FFT results for the shell and core, respectively
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Figure 1: a Schematic diagram of a single CNF/TiO2 core–shell NW device. b SEM image of a device used in the study. Inset shows a four-probe device used to measure contact resistance and resistivity. c TEM image showing the core–shell structure of the CNF/TiO2 NW. The yellow dashed line shows the interface between the TiO2 shell and CNF core. d Microstructure of the core–shell NW, insets give the FFT results for the shell and core, respectively

Mentions: The CNF/TiO2 core–shell NW samples were prepared by depositing a particulate anatase TiO2 film for 30 min at 500 °C onto a vertically aligned carbon nanofiber (VACNF) array by metal–organic chemical vapor deposition (MOCVD) [17]. The VACNFs used are a subset of multi-walled CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) on silicon substrates [18-20]. The details of the growth have been described elsewhere [16,17]. To fabricate individual CNF/TiO2 core–shell NW devices as schematically shown in Fig. 1a, the as-grown NWs were dispersed into ethanol and transferred onto a silicon substrate covered with 500 nm thermally grown silicon dioxide. Bi-layer electron beam resist (PMMA/MMA-MAA) was used in the electron beam lithography (EBL) process for the definition of two or four electrodes. Before electrode deposition, a subset of the samples was treated with O2 plasma at 20 W for 30 s via reactive ion etching (RIE) at a pressure of 7.1 mTorr in order to remove any possible residual electron beam resist and other surface contaminants that could prevent Ohmic contact between the electrodes and TiO2 shell. Ti (15 nm)/Au (120 nm) electrodes were deposited by using electron beam evaporation through the EBL-defined mask followed by liftoff with acetone. After fabrication, all samples were annealed at 400 °C for 30 min with a temperature ramping rate of 15 °C/min. The annealing was performed in vacuum at a pressure of ~10−5 Torr or better, with the intention of avoiding oxidation of Ti in the bottom layer of the electrode and desorbing any possible residual chemicals on the surface of the nanowire due to the above processes. To attach dye molecules onto the TiO2 surface of the CNF/TiO2 core–shell NW device, the O2 plasma treated and untreated samples were soaked in 0.2 mM ethanol solution of cis-bis (isothiocyanoto) bis (2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) bis- tetrabutylammonium dye (N719, Solaronix) for 12 h and blown dry with pure N2. The soaking and mounting of the samples were performed in dark in order to limit the premature exposure of the devices to light. The prepared samples were enclosed in an aluminum box in order to measure the dark I–V characteristics before exposure to one sun illumination (100 mW/cm2) produced by a solar simulator outfitted with an AM 1.5 G filter (Newport).


Investigation into Photoconductivity in Single CNF/TiO(2)-Dye Core-Shell Nanowire Devices.

Li Z, Rochford C, Javier Baca F, Liu J, Li J, Wu J - Nanoscale Res Lett (2010)

a Schematic diagram of a single CNF/TiO2 core–shell NW device. b SEM image of a device used in the study. Inset shows a four-probe device used to measure contact resistance and resistivity. c TEM image showing the core–shell structure of the CNF/TiO2 NW. The yellow dashed line shows the interface between the TiO2 shell and CNF core. d Microstructure of the core–shell NW, insets give the FFT results for the shell and core, respectively
© Copyright Policy
Related In: Results  -  Collection

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Figure 1: a Schematic diagram of a single CNF/TiO2 core–shell NW device. b SEM image of a device used in the study. Inset shows a four-probe device used to measure contact resistance and resistivity. c TEM image showing the core–shell structure of the CNF/TiO2 NW. The yellow dashed line shows the interface between the TiO2 shell and CNF core. d Microstructure of the core–shell NW, insets give the FFT results for the shell and core, respectively
Mentions: The CNF/TiO2 core–shell NW samples were prepared by depositing a particulate anatase TiO2 film for 30 min at 500 °C onto a vertically aligned carbon nanofiber (VACNF) array by metal–organic chemical vapor deposition (MOCVD) [17]. The VACNFs used are a subset of multi-walled CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) on silicon substrates [18-20]. The details of the growth have been described elsewhere [16,17]. To fabricate individual CNF/TiO2 core–shell NW devices as schematically shown in Fig. 1a, the as-grown NWs were dispersed into ethanol and transferred onto a silicon substrate covered with 500 nm thermally grown silicon dioxide. Bi-layer electron beam resist (PMMA/MMA-MAA) was used in the electron beam lithography (EBL) process for the definition of two or four electrodes. Before electrode deposition, a subset of the samples was treated with O2 plasma at 20 W for 30 s via reactive ion etching (RIE) at a pressure of 7.1 mTorr in order to remove any possible residual electron beam resist and other surface contaminants that could prevent Ohmic contact between the electrodes and TiO2 shell. Ti (15 nm)/Au (120 nm) electrodes were deposited by using electron beam evaporation through the EBL-defined mask followed by liftoff with acetone. After fabrication, all samples were annealed at 400 °C for 30 min with a temperature ramping rate of 15 °C/min. The annealing was performed in vacuum at a pressure of ~10−5 Torr or better, with the intention of avoiding oxidation of Ti in the bottom layer of the electrode and desorbing any possible residual chemicals on the surface of the nanowire due to the above processes. To attach dye molecules onto the TiO2 surface of the CNF/TiO2 core–shell NW device, the O2 plasma treated and untreated samples were soaked in 0.2 mM ethanol solution of cis-bis (isothiocyanoto) bis (2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) bis- tetrabutylammonium dye (N719, Solaronix) for 12 h and blown dry with pure N2. The soaking and mounting of the samples were performed in dark in order to limit the premature exposure of the devices to light. The prepared samples were enclosed in an aluminum box in order to measure the dark I–V characteristics before exposure to one sun illumination (100 mW/cm2) produced by a solar simulator outfitted with an AM 1.5 G filter (Newport).

Bottom Line: A vertically aligned carbon nanofiber array coated with anatase TiO(2) (CNF/TiO(2)) is an attractive possible replacement for the sintered TiO(2) nanoparticle network in the original dye-sensitized solar cell (DSSC) design due to the potential for improved charge transport and reduced charge recombination.Although the reported efficiency of 1.1% in these modified DSSC's is encouraging, the limiting factors must be identified before a higher efficiency can be obtained.This work employs a single nanowire approach to investigate the charge transport in individual CNF/TiO(2) core-shell nanowires with adsorbed N719 dye molecules in dark and under illumination.

View Article: PubMed Central - HTML - PubMed

ABSTRACT
A vertically aligned carbon nanofiber array coated with anatase TiO(2) (CNF/TiO(2)) is an attractive possible replacement for the sintered TiO(2) nanoparticle network in the original dye-sensitized solar cell (DSSC) design due to the potential for improved charge transport and reduced charge recombination. Although the reported efficiency of 1.1% in these modified DSSC's is encouraging, the limiting factors must be identified before a higher efficiency can be obtained. This work employs a single nanowire approach to investigate the charge transport in individual CNF/TiO(2) core-shell nanowires with adsorbed N719 dye molecules in dark and under illumination. The results shed light on the role of charge traps and dye adsorption on the (photo) conductivity of nanocrystalline TiO(2) CNF's as related to dye-sensitized solar cell performance.

No MeSH data available.


Related in: MedlinePlus