Showing papers by "Kuo-Chuan Ho published in 2014"

Organic dyes containing carbazole as donor and π-linker: optical, electrochemical, and photovoltaic properties.

Abstract: A series of new metal free organic dyes containing carbazole as donor and π-linker have been synthesized and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). The carbazole functionalized at C-2 and C-7 served as electron-rich bridge. The donor property of the carbazole is substantially enhanced on introduction of tert-butyl groups at C-3 and C-6 positions and the oxidation propensity of the dyes increased on insertion of thiophene unit in the conjugation pathway. These structural modifications fine-tuned the optical and electrochemical properties of the dyes. Additionally, the presence of tert-butyl groups on the carbazole nucleus minimized the intermolecular interactions which benefited the performance of DSSCs. The dyes served as efficient sensitizers in DSSCs owing to their promising optical and electrochemical properties. The efficiency of DSSCs utilizing these dyes as sensitizers ranged from 4.22 to 6.04%. The tert-butyl groups were found to suppress the recombination of...

Single layer of nickel hydroxide nanoparticles covered on a porous Ni foam and its application for highly sensitive non-enzymatic glucose sensor

Abstract: A single layer of nickel hydroxide nanoparticles (Ni(OH)2 NPs) was covered on the full surface of a porous Ni foam by simply applying an electrochemical cyclic voltammetric (CV) treatment on a bare Ni foam substrate for 100 cycles in 1.0 M NaOH solution. The surface morphology of the obtained Ni(OH)2 NPs/Ni foam electrode was examined by scanning electron microscopy. The thickness of the Ni(OH)2 NPs layer on the electrode was estimated by X-ray photoelectron spectroscopy with Ar+ ion etching. In CV measurement, the Ni(OH)2 NPs/Ni foam electrode exhibited excellent electrocatalytic ability toward glucose in NaOH solution. The Ni(OH)2 NPs/Ni foam electrode was successfully used for the quantification of glucose by an amperometric method. The sensing parameters include a high sensitivity of 1950.3 μA/mM-cm2, a linear range from 0.6 to 6.0 mM, a detection limit of 0.16 μM, and an applied potential of 0.45 V (vs. Ag/AgCl/KCl sat’d). The excellent performances obtained in the interference test, the long-term durability test in atmosphere, and the reproducibility test of the Ni(OH)2 NPs/Ni foam sensor indicate the applicability of the proposed electrode as a reliable non-enzymatic glucose sensor.

Y-shaped metal-free D–π–(A)2 sensitizers for high-performance dye-sensitized solar cells

Abstract: A series of 2,3,5-substituted thiophene-based metal-free dyes with two anchoring groups, D–π–(A)2 (DA), were synthesized for application in DSSCs. Different arylamines and 2-cyanoacrylic acid were used as the electron donor and the electron acceptor, respectively. The DSSC based on DA5 has the best power conversion efficiency (7.28%) among all devices, which is 2 times higher than that of S1 with only one anchoring group. With addition of a co-adsorbent, CDCA, the device performance of all the DA-based DSSCs are improved by 1.03 to 2-fold, with the best efficiency (7.87%) reaching 95% of that of the N719-based standard cell (8.28%). Compared with the S1 congener with only one anchor, the DA dyes can more effectively suppress charge recombination and increase electron injection efficiency, leading to higher open-circuit voltage and short-circuit current.

A high performance electrochemical sensor for acetaminophen based on a rGO–PEDOT nanotube composite modified electrode

Abstract: In this study, we perform an electrochemical sensing using a conductive composite film containing reduced graphene oxide (rGO) and poly(3,4-ethylenedioxythiophene) nanotubes (PEDOT NTs) as an electrode modifier on a glassy carbon electrode (GCE). Scanning electron microscopy suggests that the rGO covers the surface of GCE uniformly and the PEDOT NTs act as a conducting bridge to connect the isolated rGO sheets. By combining these two materials, the conductivity and the surface coverage of the film can be enhanced, which is beneficial for electrochemical sensing. The rGO–PEDOT NT composite modified electrode is applied for an effective sensor to analyze acetaminophen. The obtained electrochemical activity is much higher than those obtained by the rGO- and PEDOT NT-modified electrodes; the higher electrochemical activity may be attributed to the higher conductivity and greater coverage of the rGO–PEDOT NT composite film on the GCE. Furthermore, interference tests indicate that the rGO–PEDOT NT composite modified electrode exhibits high selectivity toward the analyte. This novel method for combining the rGO and PEDOT NTs establishes a new class of carbon material-based electrodes for electrochemical sensors.

Multiwalled Carbon Nanotube@Reduced Graphene Oxide Nanoribbon as the Counter Electrode for Dye-Sensitized Solar Cells

Abstract: In this study, a new core–shell heterostructure of multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) was prepared by modified microwave-assisted synthesis step and a chemical reduction. The core–shell heterostructure of MWCNT@rGONR was used as the catalytic film of the counter electrode (CE) of a dye-sensitized solar cell (DSSC). The chemical state and the degree of defects on the surface of MWCNT@rGONR were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectra, respectively. Transmission electron microscopy (TEM) image of the film of MWCNT@rGONR shows graphene sheet, covering on a MWCNT, indicating a core of the carbon nanotube and its shell of graphene. Photocurrent density–voltage characteristics of the DSSCs, using commercial graphene nanopowder (GNP), MWCNT, and MWCNT@rGONR as the CE materials were obtained at 100 mW cm–2. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrocatalytic abilities of the films...

Organic Dyes Containing Fluorene Decorated with Imidazole Units for Dye-Sensitized Solar Cells

Abstract: New organic dyes containing fluorene functionalized with two imidazole chromophores as donors and cyanoacrylic acid acceptors have been synthesized and successfully demonstrated as sensitizers in nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). The monoimidazole analogues were also synthesized for comparison. The Sommelet reaction of bromomethylated 2-bromo-9,9-diethyl-9H-fluorene produced the key precursor 7-bromo-9,9-diethyl-9H-fluorene-2,4-dicarbaldehyde required for the preparation of imidazole-functionalized fluorenes. Since the dyes possess weak donor segment, the electron-richness of the conjugation pathway dictated the optical, electrochemical, and photovoltaic properties of the dyes. The dyes served as sensitizers in DSSC and exhibited moderate efficiency up to 3.44%. The additional imidazole present on the fluorene has been found to retard the electron recombination due to the bulkier hydrophobic environment and led to high open-circuit voltage in the devices.

A coral-like film of Ni@NiS with core-shell particles for the counter electrode of an efficient dye-sensitized solar cell

Abstract: A coral-like film of nickel@nickel sulfide (Ni@NiS) was obtained on a conducting glass through an electrochemical method, in which the Ni functioned as a template. Three types of Ni thin films were electrodeposited on fluorine-doped tin oxide (FTO) substrates by a pulse current technique at the passed charge densities of 100, 200, and 300 mC cm−2, which rendered custard apple-like, coral-like, and cracked nanostructures, respectively. Subsequently, nickel sulfide films were coated on these Ni films by using a pulse potential technique. Due to the template effect of the Ni films, the composite films of Ni@NiS also assumed the same structures as those of their nickel templates. In each case of the films the particle of the film assumed a core–shell structure. The Ni@NiS coated FTO glasses were used as the counter electrodes for dye-sensitized solar cells (DSSCs). The DSSC with the coral-like Ni@NiS film on its counter electrode exhibits the highest power conversion efficiency (η) of 7.84%, while the DSSC with platinum film on its counter electrode shows an η of 8.11%. The coral-like Ni@NiS film exhibits multiple functions, i.e., large surface area, high conductivity, and great electrocatalytic ability for iodine/triiodine (I−/I3−) reduction. X-ray photoelectron spectroscopy (XPS), X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), and four-point probe technique were used to characterize the films. The photovoltaic parameters are substantiated using incident photon-to-current conversion efficiency (IPCE) curves, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization plots. The IPCE curves were further used to calculate theoretical short-current densities of the cells.

Dye-sensitized solar cells with reduced graphene oxide as the counter electrode prepared by a green photothermal reduction process.

Abstract: Highly conductive reduced graphene oxide (rGO) with good electrocatalytic ability for reducing triiodide ions (I3(-)) is a promising catalyst for the counter electrode (CE) of dye-sensitized solar cells (DSSCs). However, hazardous chemical reducing agents or energy-consuming thermal treatments are required for preparing rGO from graphene oxide (GO). Therefore, it is necessary to find other effective and green reduction processes for the preparation of rGO and to fabricate rGO-based DSSCs. In this study, GO was prepared using a modified Hummers method from graphite powder, and further reduced to rGO through a photothermal reduction process (to give P-rGO). P-rGO shows better electrocatalytic ability due mainly to its high standard heterogeneous rate constant for I3(-) reduction and in part to its considerable electrochemical surface area. The corresponding DSSC shows a higher cell efficiency (η) of 7.62% than that of the cell with a GO-based CE (η=0.03%). When the low-temperature photothermal reduction process is applied to all-flexible plastic DSSCs, the DSSC with a P-rGO CE shows an η of 4.16%.

Organic dyes containing fluoren-9-ylidene chromophores for efficient dye-sensitized solar cells

Abstract: Novel organic sensitizers comprising one or two fluorenylidene moieties in the donor part of triarylamine, cyanoacrylic acid as the acceptor/anchoring group and a fluorene and oligothiophene spacer in a D–π–A architecture have been synthesized and characterized as sensitizers for nanocrystalline TiO2-based dye-sensitized solar cells. Their optical, electrochemical and photovoltaic properties are compared with the electron accepting dicyanovinyl unit containing the organic sensitizer. Incorporation of the fluorenylidene moiety dominates the optical properties of the dyes in terms of relatively broad and high molar extinction coefficient absorption when compared to the dicyanovinyl derivatives. Theoretical investigations using TDDFT simulations indicate that the trends in the excitation energies are consistent with the solution spectral data for higher wavelength absorption and the lower wavelength absorptions attributed to the amine to auxiliary acceptor charge transfer. The electrochemical properties are influenced by the number of fluorenylidene chromophores and the electron richness of the linking segment. The dye-sensitized solar cells fabricated using fluorenylidene-based sensitizers showed higher power conversion efficiency than the dicyanovinyl derivatives attributed to their higher photocurrent density. A fluorenylidene-based dye exhibited a high power conversion efficiency of 6.13% under full sunlight (AM 1.5G, 100 mW cm−2).

Poly(3,4-ethylenedioxythiophene) (PEDOT) hollow microflowers and their application for nitrite sensing

Abstract: A film of poly(3,4-ethylenedioxythiophene) hollow microflowers (PEDOT-HMF) was electrodeposited on a fluorine-doped tin oxide (FTO) glass substrate by using a film of ZnO microflowers as the template. Each of the PEDOT hollow microflowers shows several 2D nanopetals. Various charge densities were applied for the deposition of the PEDOT film, intending to investigate the charge effect on the film's morphology. The FTO glass with the film of PEDOT-HMF (hereafter PEDOT-HMF modified electrode) was used as a nitrite sensor. A dramatic improvement was observed in the sensitivity of the PEDOT-HMF electrode, with reference to that of a flat PEDOT electrode. Through an amperometric detection, the sensitivity and limit of detection (LOD) of the sensor were found to be 255.2 μA mM −1 cm −2 and 0.59 μM, respectively. The linear range of the PEDOT-HMF electrode was between 50 and 7500 μM, and was observed to be larger than that of the corresponding PEDOT electrode. An interference effect was studied, using different kinds of salts that contain anionic interferences in the detection of nitrite. All the ions of the salts, except SO 3 2− , showed negligible effect on the determination of nitrite.

Novel polymer gel electrolyte with organic solvents for quasi-solid-state dye-sensitized solar cells.

Abstract: A cross-linked copolymer was previously synthesized from poly(oxyethylene) diamine (POE-amine) and an aromatic anhydride and cured to generate an amide-imide cross-linking structure. The copolymer containing several chemical groups such as POE, amido acids, and imide, enabled to absorb liquid electrolytes in methoxypropionitrile (MPN) for suitable uses in dye-sensitized solar cells. To establish the advantages of polymer gel electrolytes (PGE), the same copolymer was studied by using different electrolyte solvents including propylene carbonate (PC), dimethylformamide, and N-methyl-2-pyrrolidone, and shown their long-term stability. The morphology of the copolymer after absorbing liquid electrolytes in these solvents was proven the same as a 3D interconnected nanochannels, evidenced field emission-scanning electron microscopy. Among these solvents, PC was selected as the optimized PGE, which demostrated a higher power conversion efficiency (8.31%) than that of the liquid electrolyte (7.89%). In particular,...

Nanocomposite Graphene/Pt Electrocatalyst as Economical Counter Electrode for Dye‐Sensitized Solar Cells

Abstract: Platinum is the most common electrocatalyst used as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). However, due to its high cost, Pt presents an obstacle to popularizing DSSCs in energy-harvesting applications. Therefore, effective utilization of Pt and good understanding of the role of its composites are critical issues for developing low-cost DSSCs with high efficiency. In this study, a graphene/Pt nanoparticles (GN/ PtNPs) nanocomposite is synthesized as the catalyst for the CE of a DSSC. GN/PtNPs catalysts with various of PtNP loadings (10–60 wt %) are obtained by using a polyol reduction method, and are subsequently characterized by using X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. A solar-to-electricity conversion efficiency (h) of 8.79 % is achieved for a DSSC with a GN/PtNPs CE containing 20 wt% PtNPs (GN/PtNPs-20 %); this h value is higher than those of the cells with CEs consisting of pristine GN (7.65 %) or sputtered Pt (sPt, 8.58 %). Electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel polarization plots reveal that the higher h value of the cell with GN/PtNPs-20 % is due to the higher electrocatalytic ability of the CE for the reduction of triiodide ions (I3 � ) and the reduced charge-transfer resistance at the CE/electrolyte interface. The excellent electrocatalytic performance of GN/PtNPs-20 % is attributed essentially to its high intrinsic heterogeneous rate constant for the I3 � reduction reaction and partly to its high electrochemical surface area, which are quantitatively calculated by means of a rotating disk electrode system and the Koutecky ´–Levich equation.

Tunable electrofluorochromic device from electrochemically controlled complementary fluorescent conjugated polymer films.

Abstract: The fluorescent behavior of the electrofluorochromic devices (Type I) of greenish-yellow emitting P1 and blue emitting P2 can be reversibly switched between the nonfluorescent (oxidized) state and the fluorescent (neutral) state with a superb on/off ratio of 23.8 and 21.9, respectively. Moreover, a tunable electrofluorochromic device (Type II) based on two P1 and P2 polymeric layers that are coated individually on two independent ITO electrodes shows switchable blue-white-(greenish-yellow) multifluorescence states.

Functional tuning of phenothiazine-based dyes by a benzimidazole auxiliary chromophore: an account of optical and photovoltaic studies

Abstract: We have designed and synthesized a series of organic dyes featuring phenothiazine donors containing an N-phenylbenzimidazole substituent and a cyanoacrylic acid acceptor. Benzimidazole incorporation red-shifted the charge transfer transition and increased the molar extinction coefficient of the peak. It also helped to fine-tune the HOMO and LUMO energies of the dyes due to the electron-withdrawing nature of the benzimidazole. The dye-sensitized solar cells fabricated using the dyes possessing N-phenylbenzimidazole showed efficiency better than the analogous dye without benzimidazole. The hike in the efficiency resulted from the increase in short-circuit current and open circuit voltage. The electrochemical impedance spectroscopy of the devices revealed that the integration of benzimidazole in the dye enhances the life time of the injected electrons in the conduction band of TiO2 and resists electron recombination at the TiO2/dye/electrolyte interface.

Ionic liquid with a dual-redox couple for efficient dye-sensitized solar cells.

Abstract: A new type of ionic liquid that contains a nitroxide radical (NOC) and iodide as two redox couples, JC-IL, has been suc- cessfully synthesized for high-performance dye-sensitized solar cells (DSSCs). Both of the redox couples exhibit distinct redox potentials and attractive electrochemical characteristics. The UV/Vis absorption spectra of JC-IL shows a low-intensity peak compared to the strong absorption of I2 in the wavelength region of 350-500 nm. The high open-circuit voltage of DSSCs with JC-IL is over 850 mV, which is approximately 150 mV higher than that of the DSSCs with a standard iodide electro- lyte. The dramatic increase in the standard heterogeneous electron-transfer rate constant leads to an increase in the short-circuit current for JC-IL compared to that of 2,2,6,6-tetra- methylpiperidin-N-oxyl (TEMPO). DSSCs with the JC-IL electro- lyte show promising cell efficiencies if coupled with dyes CR147 (8.12 %) or D149 (6.76 %). The efficiencies of the DSSCs based on the JC-IL electrolyte are higher than those of DSSCs based on either TEMPO electrolyte or standard iodide electro- lyte alone.

Synthesis of a novel amphiphilic polymeric ionic liquid and its application in quasi-solid-state dye-sensitized solar cells

Abstract: A novel polymeric ionic liquid (PIL), poly(oxyethylene)-imide-imidazole complex coupled with iodide anions (coded as POEI-II), was synthesized for preparing the gel electrolyte for quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). Herein, POEI-II, which acts simultaneously as a redox mediator in the electrolyte and a polymer for the gelation of an organic solvent-based electrolyte, was used to improve cell durability. In the structure of POEI-II, the presence of the POE segment can chelate lithium cations (Li+) within the electrolyte to improve the open-circuit voltage (VOC) of a QSS-DSSC, and enable a strong dipole–dipole lone-pair electron interaction with iodide ions (I−) of electrolyte composition rendering the high ionic conductivity and the diffusivity of a redox couple within the gel electrolyte. Consequently, the QSS-DSSC with the POEI-II gel electrolyte reaches a high cell efficiency of 7.19%. In addition, 5 wt% of multi-wall carbon nanotubes (MWCNTs) are incorporated into the POEI-II gel electrolyte as the extended electron transfer material (EETM) to facilitate charge transfer from the counter electrode to the redox mediator, which benefits the dye regeneration more efficiently. Meanwhile, the POE segments in POEI-II can prevent the MWCNTs from aggregation, which makes the well dispersed MWCNTs largely exposed to redox mediators. The highest cell efficiency of 7.65% was achieved by using the POEI-II/MWCNT gel electrolyte and it showed an unfailing durability of greater than 1000 h under 50 °C. This properly designed PIL paves a promising way for developing highly efficient and durable QSS-DSSCs.

Structure–Performance Correlations of Organic Dyes with an Electron-Deficient Diphenylquinoxaline Moiety for Dye-Sensitized Solar Cells

Abstract: The high performances of dye-sensitized solar cells (DSSCs) based on seven new dyes are disclosed. Herein, the synthesis and electrochemical and photophysical properties of a series of intentionally designed dipolar organic dyes and their application in DSSCs are reported. The molecular structures of the seven organic dyes are composed of a triphenylamine group as an electron donor, a cyanoacrylic acid as an electron acceptor, and an electron-deficient diphenylquinoxaline moiety integrated in the π-conjugated spacer between the electron donor and acceptor moieties. The DSSCs based on the dye DJ104 gave the best overall cell performance of 8.06 %; the efficiency of the DSSC based on the standard N719 dye under the same experimental conditions was 8.82 %. The spectral coverage of incident photon-to-electron conversion efficiencies extends to the onset at the near-infrared region due to strong internal charge-transfer transition as well as the effect of electron-deficient diphenylquinoxaline to lower the energy gap in these organic dyes. A combined tetraphenyl segment as a hydrophobic barrier in these organic dyes effectively slows down the charge recombination from TiO2 to the electrolyte and boosts the photovoltage, comparable to their Ru(II) counterparts. Detailed spectroscopic studies have revealed the dye structure-cell performance correlations, to allow future design of efficient light-harvesting organic dyes.

Transparent graphene–platinum nanohybrid films for counter electrodes in high efficiency dye-sensitized solar cells

Abstract: A dispersion of platinum-on-graphene was prepared essentially by a two-step process, involving uniform distribution of graphene nanoplatelets in a cosolvent of ethanol–water in the presence of a polymeric dispersant and subsequent in situ reduction of dihydrogen hexachloroplatinate to metallic platinum on the graphene surface. The process generated platinum nanoparticles (PtNPs) of ca. 4.0–10 nm in diameter on the graphene surface. The platinum-on-graphene dispersion was coated on an FTO glass to prepare a counter electrode (CE) for a dye-sensitized solar cell (DSSC). The hybrid film of platinum nanoparticles and graphene nanoplatelets (PtNP/GN) showed a transparency of 70% at 550 nm, indicating its suitability as a CE material for a rear-illuminated DSSC. The DSSC with the CE having the film of PtNP/GN exhibited a power conversion efficiency (η) of 8.00%, superior to 7.14% of the DSSC with a conventional sputtered platinum (s-Pt) CE. In the case of rear-illumination the DSSC showed an η of 7.01%, while the DSSC with the conventional s-Pt showed an η of only 2.36%. HRTEM and FE-SEM were used to observe the dispersion of the hybrid material in the solvent, UV-vis spectroscopy and cyclic voltammetry were used to characterize the films, and IPCE spectra and electrochemical impedance spectra were used to explain the photovoltaic parameters of the DSSCs.

Electrochemical synthesis of a double‐layer film of ZnO nanosheets/nanoparticles and its application for dye‐sensitized solar cells

Abstract: A double-layer film, consisting of an upper layer of ZnO nanosheets and a lower layer of ZnO nanoparticles (designated as ZnONS/NP), was synthesized for the photoanode of a dye-sensitized solar cell (DSSC) by a one-step potentiostatic electrodeposition on a conducting fluorine-doped tin oxide substrate at 70 °C in a solution containing zinc nitrate and sodium acetate, followed by the pyrolysis of the film at 300 °C. The growth mechanism of the double-layer nanostructure was studied by monitoring the morphological changes at various periods of electrodeposition. The effects of the concentration of acetate anion on the morphology of the double-layer structure were also studied. The double-layer film of ZnONS/NP showed a better self-established light scattering property, compared with that of a thin film of ZnO nanoparticles, prepared without acetate anion. The concentration of an acetate anion in the electrolyte for the electrodeposition of the double-layer film, the electrodeposition period, and the period for dye adsorption were optimized for obtaining the best performance for a DSSC with a photoanode consisting of the double layer. A metal-free dye, coded as D149, was used in this research. A conversion efficiency of 4.65% was achieved for a DSSC (0.2376 cm2) with the photoanode, consisting of the double-layer film, under 100 mW/cm2 illumination in the wavelength range of 400–800 nm. X-ray diffraction patterns, thermo gravimetric curves, elemental analysis, scanning electron microscopic images, transmission electron microscopic image, transmission spectra, and electrochemical impedance spectra were used to explain observations. Copyright © 2012 John Wiley & Sons, Ltd.

Self-assembled all-conjugated block copolymer as an effective hole conductor for solid-state dye-sensitized solar cells.

Abstract: An all-conjugated diblock copolymer, poly(2,5-dihexyloxy-p-phenylene)-b-poly(3-hexylthiophene) (PPP-b-P3HT), was synthesized and applied as a hole transport material (HTM) for the fabrication of solid-state dye-sensitized solar cells (ss-DSCs). This copolymer is characterized by an enhanced crystallinity, enabling its P3HT component to self-organize into interpenetrated and long-range-ordered crystalline fibrils upon spin-drying and ultimately endowing itself to have a faster hole mobility than that of the parent P3HT homopolymer. Transient photovoltage measurements indicate that the photovoltaic cell based on PPP-b-P3HT as the HTM has a longer electron lifetime than that of the reference device based on P3HT homopolymer. Moreover, comparing the two ss-DSCs in terms of the electrochemical impedance spectra reveals that the electron density in the TiO2 conduction band is substantially higher in the PPP-b-P3HT device than in the P3HT cell. Above observations suggest that the PPP block facilitates an intimat...

Surface modification of TiO2 nanotube arrays with Y2O3 barrier layer: controlling charge recombination dynamics in dye-sensitized solar cells

Abstract: Fast electron transport, large specific surface area, and slow interfacial electron recombination are indispensable features for efficient photoelectrodes of dye-sensitized solar cells (DSSCs). Highly ordered TiO2 nanotubes (TNT) with advanced architecture of high surface-to-volume ratio and open-up geometry for providing direct electron/ion transport channels is applied on a flexible photoanode in this study. Because several micrometers of semiconductor are required for the diffusion of electrons, which are surrounded by electron acceptors at a distance of only several nanometers, a wide band gap barrier layer of Y2O3 is coated on TNT to retard back-transfer of electrons to the electrolyte or to the oxidized dye molecules by electrodepositing Y(OH)3 on the TNT surfaces and subsequently annealing the samples. By adjusting the charge capacity for Y(OH)3 electrodeposition, the charge recombination dynamics in the pertinent DSSC can be easily controlled. This barrier layer also enhances dye adsorption and therefore increases the volume of the optically active component due to the more basic surface of Y2O3 for more carboxyl groups in a dye molecule adsorbing onto the surface. A higher light-to-power conversion efficiency (η) of 6.52% is obtained for the pertinent DSSC compared with a reference cell with non-coated TNT (η = 5.35%), exhibiting an enhancement of 22% in η.