Free-standing TiO2 Nanotube Arrays Research Articles

Construction of nanoreactors on TiO2 nanotube arrays as a POCT device for sensitive colorimetric detection

With increasing attention to personalized healthcare, miniaturized and easily implementable devices are desired for point-of-care testing (POCT). Herein, hydrophilic patterns were designed on freestanding TiO2 nanotube arrays (TiNTs) as nanoreactors for a naked-eye colorimetric assay. With a high aspect ratio, TiNTs can provide a long observation length combined with a limited volume. Moreover, by combining the photocatalytic property of TiO2 and spatiotemporal controllability of light, hydrophilic nanoreactors were fabricated with minimal volume, and thus the indicator and analyte are limited in a confined void by the hydrophobic surroundings, thus allowing a higher sensitivity for sensing. We believe the proposed sensing platform could provide a promising strategy in developing POCT devices for routine health monitoring.

Betavoltaic-powered electrochemical cells using TiO2 nanotube arrays incorporated with carbon nanotubes

Highly efficient direct energy conversion utilizing the betavoltaic effect is a promising alternative for developing of maintenance-free and long-life self-generating power cells. This work demonstrates a betavoltaic-powered electrochemical cell (BPEC) using free-standing TiO2 nanotube arrays (TNTAs) incorporated with single-wall carbon nanotubes (SWCNTs) as the beta anode, a polyiodide (I−/I3−) solution as the electrolyte, and a radioisotope 63Ni/Ni sheet as the cathode as well as the irradiation source. Freestanding TNTAs were fabricated using electrochemical anodization. Monte Carlo simulations were used to investigate the interaction of the incident beta particles with the TNTAs structure. Experimentally, the photoelectrochemical characteristics were used to optimize the structural design of the BPECs. The optimum BPEC exhibited an energy conversion efficiency of 8.74% with an open circuit voltage of 0.26 V and a short circuit current density of 0.87 μA/cm2. The enhanced betavoltaic effect is attributed to the highly efficient separation and transport of beta-generated carriers through the enhanced beta-electrochemical redox reactions in the 3-D TiO2/liquid heterojunction as well as the extensive SWCNTs conductive network.

Effect of Au Nanoparticles and Scattering Layer in Dye-Sensitized Solar Cells Based on Freestanding TiO2 Nanotube Arrays.

The development of high efficiency dye-sensitized solar cells (DSSCs) has received tremendous attention. Many researchers have introduced new materials for use in DSSCs to achieve high efficiency. In this study, the change in power conversion efficiency (PCE) of DSSCs was investigated by introducing two types of materials—Au nanoparticles (Au NPs) and a scattering layer. A DSSC fabricated without neither Au NPs nor a scattering layer achieved a PCE of 5.85%. The PCE of a DSSC based on freestanding TiO2 nanotube arrays (f-TNTAs) with Au NPs was 6.50% due to better electron generation because the plasmonic absorption band of Au NPs is 530 nm, which matches the dye absorbance. Thus, more electrons were generated at 530 nm, which affected the PCE of the DSSC. The PCE of DSSCs based on f-TNTAs with a scattering layer was 6.61% due to better light harvesting by scattering. The scattering layer reflects all wavelengths of light that improve the light harvesting in the active layer in DSSCs. Finally, the PCE of DSSCs based on the f-TNTAs with Au NPs and a scattering layer was 7.12% due to the synergy of better electron generation and light harvesting by plasmonics and scattering. The application of Au NPs and a scattering layer is a promising research area for DSSCs as they can increase the electron generation and light harvesting ability.

Synthesis and density functional theory study of free-standing Fe-doped TiO2 nanotube array film for H2S gas sensing properties at low temperature

Abstract To analyze the sensing performance of the TiO2 nanotube (TiNT) array film gas sensor to H2S at low working temperature, the free-standing Fe-doped TiNT array films were synthesized using the one-step anodic oxidation method followed by immersion and annealing processes. The results obtained from the field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectra and ultraviolet–visible spectra methods indicate that the lattice of TiO2 was doped by iron ions. Subsequently, compared with undoped TiO2, the response intensity, response and recovery times of the gas sensor based on Fe-doped TiNT array film to 50 ppm H2S at 100 °C were improved. Furthermore, the improved selectivity and stability to H2S were also obtained with the Fe-doped TiNT gas sensor. Finally, based on the Density Functional Theory (DFT), the band structure of Fe-doped TiO2 and the electronic density of states of H2S and the compared gases are calculated and used for the systematical analysis of sensing and selectivity mechanisms of the Fe-doped TiNT gas sensor at low working temperature.

MoS2-supported on free-standing TiO2-nanotubes for efficient hydrogen evolution reaction

The electrochemical production of hydrogen is a promising and flexible approach towards the conversion of intermittent renewable energy sources into clean chemical fuel. However, low-cost, efficient, and durable electrocatalysts are yet to be developed to attain economies of scale in hydrogen generation. In this study, we fabricated highly ordered free-standing TiO2 nanotube arrays (TiO2-NTs), by simply anodizing Ti foils. The tube length, diameter, wall thickness, and surface structure of the TiO2-NTs can be controlled by adjusting the anodization conditions. Subsequently, we synthesized and supported MoS2 layers on free-standing TiO2-NTs as an active material for the hydrogen evolution reaction (HER), using a slow evaporation method. The layers of MoS2 uniformly disperse on the entire surface of the TiO2-NTs composite. The electrochemical test shows that the MoS2-supported free-standing (MoS2/TiO2-NTs) system exhibits excellent HER performance in acidic media with a low overpotential at 10 mA cm−2 (170 mV), as well as small Tafel slope (70 mV decade−1). Also, the MoS2/TiO2-NTs displays superior durability for HER after 5000 continuous potential cycles between −0.4 and + 0.2 (V vs. RHE). Our results demonstrate the potential application of MoS2/TiO2-NTs composite for cost-effective electrochemical production of hydrogen.

Au-Embedded and Carbon-Doped Freestanding TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells for Better Energy Conversion Efficiency.

Dye-sensitized solar cells (DSSCs) are fabricated with freestanding TiO2 nanotube arrays (TNTAs) which are incorporated with Au nanoparticles (NPs) and carbon materials via electrodeposition and chemical vapor deposition (CVD) method to create a plasmonic effect and better electron transport that will enhance their energy conversion efficiency (ECE). The ECE of DSSCs based on the freestanding TNTAs is 5.87%. The ECE of DSSCs, based on the freestanding TNTAs with Au NPs or carbon materials, is 6.57% or 6.59%, respectively, and the final results of DSSCs according to the freestanding TNTAs with Au NPs and carbon materials is increased from 5.87% to 7.24%, which is an enhancement of 23.34% owing to plasmonic effect and better electron transport. Au NPs are incorporated into the channel of freestanding TNTAs and are characterized by CS-corrected-field emission transmission electron microscope (Cs-FE-TEM) and elemental mapping. Carbon materials are also well-incorporated in the channel of freestanding TNTAs and are analyzed by Raman spectroscopy.

Au-Nanoparticle-Embedded Open-Ended Freestanding TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells for Better Electron Generation and Electron Transport.

Freestanding TiO2 nanotube arrays (TNTAs) were prepared by an electrochemical method, and dye-sensitized solar cells (DSSCs) were fabricated with the open-ended freestanding TNTAs incorporated with Au nanoparticles (NPs). Open-ended freestanding TNTAs were prepared by etching the barrier layer of closed-ended freestanding TNTAs using an ion milling method, and Au NPs were incorporated into the channel of the open-ended freestanding TNTAs by an electrodeposition method. The Au-NP-embedded open-ended freestanding TNTAs were applied to DSSCs to improve the energy conversion efficiency (ECE) by better electron generation and electron transport. The ECE of DSSCs based on the closed-ended freestanding TNTAs with Au NPs increased to 6.116% from 5.502% for DSSCs based on the closed-ended freestanding TNTAs without Au NPs, an enhancement of 11.16% because of better electron generation by the plasmonic and charging effects of the Au NPs. However, the ECE of DSSCs based on the closed-ended freestanding TNTAs incorporated with Au NPs for 40 s decreased from 6.116 to 5.336% because aggregation of the Au NPs led to a decrease in the open-circuit voltage (Voc) and fill factor. For enhanced ECE of DSSCs, the barrier layer of closed-ended freestanding TNTAs was etched by an ion milling method for 0, 30, 60, or 90 min to provide “open-ended freestanding TNTAs”. Then, Au NPs were incorporated into the open-ended freestanding TNTAs. After the barrier layer was completely removed by the ion milling method for 90 min, the ECE of the DSSCs reached 7.120% because the electron transport and electrolyte diffusion were improved by the elimination of the barrier layer of the freestanding TNTAs.

Plasmonic and charging effects in dye-sensitized solar cells with Au nanoparticles incorporated into the channels of freestanding TiO2 nanotube arrays by an electrodeposition method

Au nanoparticles (NPs) were incorporated into the channels of freestanding TiO2 nanotube arrays (TNTAs) by an electrodeposition method and then applied to dye-sensitized solar cells (DSSCs) for light harvesting to improve the power conversion efficiency (PCE). The average size of Au NPs incorporated into TNTA channels was approximately 70nm, and the extinction of the Au NPs by UV–vis spectra was approximately 530nm, which is similar to the absorbance of the ruthenium dye (N719) used in DSSCs. The PCE of DSSCs based on TNTAs containing Au NPs increased to 6.80% from a PCE of 5.66% without Au NPs, an enhancement of 20.14% owing to light harvesting from the NP plasmonic and charging effects. However, the PCE of DSSCs based on TNTAs with excess Au NPs decreased from 6.80% to 5.49% due to aggregation of the Au NPs, which led to a decreased open-circuit voltage and fill factor.

Improved efficiency in front-side illuminated dye sensitized solar cells based on free-standing one-dimensional TiO2 nanotube array electrodes

Although morphological disorder of nanotube structure is further down than the nanoparticular electrode, its density of traps are the hindering effects in the charge transport. In this study, crack-free TiO2 nanotube membranes, which obtained through a re-anodizing process, are fixed on transparent fluorine–tin-oxide glass by applying a few drops of Titanium Isopropoxide without needing the TiO2 powder paste. Front-side illuminated dye sensitized solar cells fabricated by undoped, N-doped and blue TiO2 nanotube membranes are investigated. The electrical characteristics of TiO2 nanotube based dye sensitized solar cells are followed by theoretical analysis using simple one-diode model. Morphology improvement is utilized to remove top irregular layers and the efficiency can be increased up to 56%. Annealing temperature, dopant, and tube orientation effects are examined on the cell efficiencies. The results show that elevating annealing temperature from 480 to 520 °C improve the cell efficiency up to 70%. Also, in the N-doped TiO2 nanotube membranes, improvement in efficiency is observed up to 40% as compared to undoped samples. Finally, different orientations of N-doped TiO2 nanotubes are studied and it is found that the through-hole morphology of N-doped TiO2 nanotube membrane shows noteworthy enhancement and an efficiency of about 8%.

Exploring the photoelectrocatalytic behavior of free-standing TiO2 nanotube arrays on transparent conductive oxide electrodes: Irradiation direction vs. alignment direction

Although one-dimensional TiO2 nanotube arrays (TNA) grown on Ti substrates via electrochemical anodization are extensively studied in photoelectrochemistry, the photo(electro)catalytic activity of TNA detached from the Ti substrates remains unexplored. Herein, we synthesize TNA samples with various pore sizes (40–100 nm) and tube lengths (4–15 μm) via two-step electrochemical anodization, and transfer them to transparent conducting oxide (i.e. fluorine-doped tin oxide; FTO) substrates in normal (n) alignment (front plane outward) and reverse (r) alignment (backplane outward). The front and back planes of the as-fabricated TNA film are the same based on X-ray diffraction (anatase structure), X-ray photoelectron spectroscopy (Ti and O), and UV–vis transmittance data, though the tubes are open in the front and closed in the back. Regardless of the direction of irradiation (SE: FTO → TNA vs. EE: TNA → FTO), longer tubes generate a higher photocurrent (Iph) due to the large light absorption. However, for the same alignment of TNA (either n- or r-TNA), SE irradiation leads to a very large Iph (e.g., nSE >nEE), whereas n-TNA consistently generates a larger Iph than r-TNA for a given irradiation direction (i.e., n >r). The photocatalytic decomposition of phenol follows the same tendency (n >r); however, the Faraday efficiency (based on the photocharge) is higher with EE (nEE 28%, rEE 20%) than SE (rSE 11%, nSE 7%) irradiation. These photoelectrochemical and photocatalytic behaviors are explained in terms of charge carrier generation (FTO/TNA vs. TNA/solution), dissimilar charge carrier transfer pathways (e− transfer through tube framework vs. h+ transfer via radial direction), and charge injection at the tube (open vs. clogged tube mouth)/solution interface. The time-resolved photoluminescence (TRPL) emission and incident photon-to-current efficiency (IPCE) are also studied to gain insight into the charge transfer kinetics.

Enhanced H2S sensing performance of cobalt doped free-standing TiO2 nanotube array film and theoretical simulation based on density functional theory

A cobalt doped free-standing TiO2 nanotube (Co-doped TiNT) array film was firstly synthesized by a one-step anodization followed by immersion method. The characterization analysis results of TiNT with the field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) proved that the doped cobalt ions had entered into the lattice of TiO2. Subsequently, the Co-doped TiNT gas sensors with different concentration of cobalt ions were developed for testing the gas-sensing properties for H2S. Compared with the undoped one, by 0.1 M Co-doping operation, working under the temperature of 300 °C, the Co-doped TiNT gas sensor was demonstrated the following superiorities: the response time and recovery time were 14 s and 4 s, which were shortened by 36.4% and 33.3%, respectively. Moreover, the Co-doped TiNT gas sensor with superior selectivity, stability and repeatability, reached the response value at 199.16 for 50 ppm H2S, which was improved by 7.6 times. Finally, based on the density functional theory (DFT), the calculated band gap of the Co-doped TiO2 decreased from 2.285 eV to 1.418 eV with a 38% decline. The mechanism simulation explained the obtained promotions in the gas sensing properties of the Co-doped TiNT gas sensor.

Semitransparent TiO2 nanotube arrays with both ends open by electrochemical anodization and ion-beam etching process

Free-standing TiO2 nanotube arrays were prepared by electrochemical anodization method. The as-prepared film was not opaque, but it was a semi-transparent. The mechanical stability of the film gradually increased with increasing film thickness. The TiO2 nanotube array films have different surface morphologies. The surface morphology of the top-surface of film was rough and all the nanotubes of top-surface were open. The compact oxide layer covered bottom-surface was smooth and all the TiO2 nanotube arrays have closed end surface morphologies. The preparation conditions were optimized and the repeatability of the film prepared at 60 V showed good results. Usually, chemical etching method was used to remove the compact oxide layer of nanotube cap. In the present work, low-energy ion-beam etching method was used to remove the compact oxide layer. The orderliness and uniformity of the bottom-surface nanotube arrays were much better than that of chemical etching method. The as-prepared film thickness was calculated as 25 μm. After the ion-beam etching process for an etching time of 1 h, the film thickness was 24 μm. The etch rate of the film was calculated as 1.6 nm min−1. The power conversion efficiency of dye-sensitized solar cell (DSC) increased with increasing film thickness.

Efficient photocatalytic degradation of gaseous N,N-dimethylformamide in tannery waste gas using doubly open-ended Ag/TiO2 nanotube array membranes

Gaseous N,N-dimethylformamide (DMF), typical volatile organic compound exhausted from manufacturing factories, may damage the health of workers under long-term exposure even at low levels. The defined geometry, porous surface and highly ordered channels make the free-standing anodic TiO2 nanotube (TiNT) arrays particularly suitable for applications of practical air purification by flow-through photocatalysis. In the present work, crystallized doubly open-ended Ag/TiNT array membranes were designed and prepared by employing a lift-off process based on an anodization-annealing-anodization-etching sequence, followed by uniform Ag nanoparticles decoration. For the photocatalytic degradation of gaseous DMF at low concentration levels close to that found in realistic pollutant air, an analytical methodology for the monitoring and determination of degradation process was developed based on the coupling of headspace sampling with gas chromatography mass spectrometry (HS-GC-MS). The doubly open-ended Ag/TiNT arrays exhibited higher removal efficiency of gaseous DMF from air compared with conventional bottom-closed Ag/TiNT arrays and pure bottomless TiNT arrays. These results indicated that the photocatalytic properties of TiNT arrays were improved with the open-bottom morphology and the Ag nanoparticles decoration. Based on the analysis with GC-MS and high performance ion chromatography (HPIC), it was found that demethylation is the main pathway of DMF degradation in photocatalytic reactions. Furthermore, decontamination of actual polluted tannery waste gas collected in leather factory proved that the photocatalysis on doubly open-ended Ag/TiNT array membrane is an efficient way and a promising application to treat air contaminated by DMF despite the complexity of various volatile organic compounds.

Enhanced Efficiency in Dye-Sensitized Solar Cells by Electron Transport and Light Scattering on Freestanding TiO₂ Nanotube Arrays.

Dye-sensitized solar cells (DSSCs) were fabricated with closed- or open-ended freestanding TiO2 nanotube arrays as photoelectrodes that were decorated with carbon materials and large TiO2 nanoparticles (NPs) to enhance energy conversion efficiency. The energy conversion efficiency of DSSCs based on open-ended freestanding TiO2 nanotube arrays increased from 4.47% to 5.39%, compared to the DSSCs based on closed-ended freestanding TiO2 nanotube arrays. In DSSCs based on the open-ended freestanding TiO2 nanotube arrays, the energy conversion efficiency with carbon materials increased from 5.39% to 6.19% due to better electron transport, and that with a scattering layer from 5.39% to 6.24% due to more light harvesting compared to the DSSCs without carbon materials or scattering layer. Moreover, the energy conversion efficiency of DSSCs based on the open-ended freestanding TiO2 nanotube arrays with both carbon materials and scattering layer increased from 5.39% to 6.98%, which is an enhancement of 29.50%. In DSSCs based on the TiO2 nanotube arrays, the carbon materials can improve electron transport by π-π conjugation, and the large TiO2 NPs can enhance the capacity to light-harvest by scattering.

A fast response and recovery H2S gas sensor based on free-standing TiO2 nanotube array films prepared by one-step anodization method

Abstract The free-standing TiO2 nanotube (TiNT) array film was firstly synthesized by a one-step anodization method. The characterization results with SEM, TEM, XRD and EDX indicated that the main compound on the TiNT array film was titania with anatase phase, and the average inner diameter of the nanotube was around 110 nm with a wall thickness of 16 nm and a layer thickness of 3.8 µm. Subsequently, the TiNT-based gas sensor was fabricated and its sensing properties toward H2S were investigated. The results showed that, operating under the optimum temperature of 300 °C, the TiNT-based gas sensor not only had excellent reversibility, selectivity and stability, but also attained the response values 4.5–26.2 to the detected H2S gas at 1–50 ppm, and good linearity between the sensor response and H2S concentration could be observed. Meanwhile, the response and recovery time of the sensor to 50 ppm H2S gas were as low as 22 s and 6 s, respectively. In addition, the growth mechanism of the free-standing TiNT array film and the gas sensing mechanism of the TiNT-based gas sensor towards H2S were also given in the article. Lastly, the outstanding gas sensing properties and easy fabrication of the TiNT-based gas sensor presented the potential industrial applications in the future.

Dual Functionalized Freestanding TiO2 Nanotube Arrays Coated with Ag Nanoparticles and Carbon Materials for Dye-Sensitized Solar Cells

Highly ordered, freestanding TiO2 nanotube arrays (TiO2 NTAs) were prepared using an electrochemical method. The barrier layer was etched to open the bottom of each array, aptly named “open-ended TiO2 NTAs”. These arrays were coated with silver nanoparticles (Ag NPs) and/or carbon materials to enhance electron generation and transport. The energy conversion efficiency of the resulting dye-sensitized solar cells (DSSCs) with open-ended freestanding TiO2 NTAs, when coated with Ag NPs, increased from 5.32% to 6.14% (by 15%) due to plasmonic interactions. Meanwhile, coating the open-ended freestanding TiO2 NTAs with carbon materials increased the energy conversion efficiency from 5.32% to 6.07% (by 14%), due to π-π conjugation. When the Ag NPs and carbon materials were simultaneously applied to the open-ended freestanding TiO2 NTAs, the energy conversion efficiency increased from 5.32% to 6.91%—an enhancement of 30%, due to the additive effects of plasmonics and π-π conjugation.

Titanate nanotube array membranes filled with polyelectrolyte brushes for proton conduction

Development of effective ion conductors with high volumetric stability is essential for micro-electrochemical devices. Herein, we report the synthesis of orderly aligned proton conductors based on polyelectrolyte brushes grafted on the surface of free-standing and through-hole TiO2 nanotube array membranes. The proton conductivity observation of the formed membranes with partially and fully filled polymers indicates that the ionic segments close to the surface play major role on proton transportation through membranes. The formed membrane exhibits promising proton conductivity at elevated temperature (0.125Scm−1 at 140°C) and the proton conductivity remains stable within the test period of time (100h). The results provide a potential nanotechnology for preparation of orderly aligned ionic conductors not only for transportation of proton but also for other ions.

Enhanced photovoltaic performance of dye sensitized solar cell using TiO2 and ZnO nanoparticles on top of free standing TiO2 nanotube arrays

Photovoltaic performance of dye sensitized solar cell (DSSC) with absorber layer of TiO2 nanotube (NT)/TiO2 nanoparticles (NPs)/ZnO NPs was investigated. Fabricated DSSC exhibits enhanced open circuit voltage, current density and power conversion efficiency compared with DSSC having absorber layer of TiO2 NT/ TiO2 NPs and TiO2 NT/ZnO NPs. To further explore the dynamics of charge transport and recombination processes, electrochemical impedance analysis, intensity modulated photovoltage spectroscopy and photocurrent spectroscopy were carried out on the fabricated DSSCs. It was found that an optimal combination of TiO2/ZnO NPs on top of TiO2 NTs reduces the electron recombination and improves transport pathways, resulting in an efficient charge collection of 99%.

Carbon-Decorated TiO2 Nanotube Membranes: A Renewable Nanofilter for Charge-Selective Enrichment of Proteins.

In this work, we design a TiO2 nanomembrane (TiNM) that can be used as a nanofilter platform for selective enrichment of specific proteins. After a first use, the photocatalytic properties of TiO2 allow the decomposition of unwanted remnants on the substrate and thus make the platform reusable. To construct this platform, we fabricate a free-standing TiO2 nanotube array and remove the bottom oxide to form a both-end-open TiNM. By pyrolysis of the natural tube wall contamination, the walls become decorated with graphitic carbon patches (C/TiNM). Owing to the large surface area, the amphiphilic nature and the charge-adjustable character, this C/TiNM can be used to extract and enrich hydrophobic charged biomolecules. Using human serum albumin (HSA) as a model protein as well as protein mixtures, we show that the composite membrane exhibits a highly enhanced loading capacity and protein selectivity and is reusable after a short UV treatment.

Ag Nanoparticle-Functionalized Open-Ended Freestanding TiO₂ Nanotube Arrays with a Scattering Layer for Improved Energy Conversion Efficiency in Dye-Sensitized Solar Cells.

Dye-sensitized solar cells (DSSCs) were fabricated using open-ended freestanding TiO2 nanotube arrays functionalized with Ag nanoparticles (NPs) in the channel to create a plasmonic effect, and then coated with large TiO2 NPs to create a scattering effect in order to improve energy conversion efficiency. Compared to closed-ended freestanding TiO2 nanotube array–based DSSCs without Ag or large TiO2 NPs, the energy conversion efficiency of closed-ended DSSCs improved by 9.21% (actual efficiency, from 5.86% to 6.40%) with Ag NPs, 6.48% (actual efficiency, from 5.86% to 6.24%) with TiO2 NPs, and 14.50% (actual efficiency, from 5.86% to 6.71%) with both Ag NPs and TiO2 NPs. By introducing Ag NPs and/or large TiO2 NPs to open-ended freestanding TiO2 nanotube array–based DSSCs, the energy conversion efficiency was improved by 9.15% (actual efficiency, from 6.12% to 6.68%) with Ag NPs and 8.17% (actual efficiency, from 6.12% to 6.62%) with TiO2 NPs, and by 15.20% (actual efficiency, from 6.12% to 7.05%) with both Ag NPs and TiO2 NPs. Moreover, compared to closed-ended freestanding TiO2 nanotube arrays, the energy conversion efficiency of open-ended freestanding TiO2 nanotube arrays increased from 6.71% to 7.05%. We demonstrate that each component—Ag NPs, TiO2 NPs, and open-ended freestanding TiO2 nanotube arrays—enhanced the energy conversion efficiency, and the use of a combination of all components in DSSCs resulted in the highest energy conversion efficiency.