Ultrathin TiO2 Layer Research Articles

Optical and photocatalytic properties of sol-gel AuNPs@TiO2 ultrathin film

The optical and photocatalytic properties of ultrathin TiO2 layers were investigated in order to stress out the effect of nanoscale thickness on the film properties. The method relies on monitoring localized surface plasmon resonance (LSPR) through UV–visible spectroscopy and enhanced Raman spectroscopy (SERS). To achieve this, TiO2 thin films were prepared using the sol–gel method on high density gold nanoparticles arrays (AuNPs). TiO2 anatase phase was obtained by thermal annealing and confirmed by XRD, HRTEM, and SERS. Our results reveal that the thinnest TiO2 layers consist of compact TiO2NPs of small dimensions and lower porosity compared to the thicker TiO2NPs layers. Subsequently, these thin TiO2 layers functionalizing AuNPs were applied in plasmonic photocatalysis, specifically for the N-demethylation of methylene blue in the visible range. When comparing layers with the same thickness (a single deposition layer with layers prepared by stacking various thin layers), the stacked layers demonstrated enhanced photocatalytic activity. This novel, stable form of TiO2 has the potential to open numerous opportunities in the fields of photocatalysis and detection.

Rational design of oxide heterostructure InGaZnO/TiO2 for high-performance thin-film transistors

In this study, hetero-structured and self-passivated oxide thin film transistors (TFTs) were fabricated, wherein the channel comprised a N2O plasma (a-IGZO:N2O) treated a-IGZO front layer and TiO2 ultra-thin back layer. A high field-effect mobility (μFE) of 40.5 cm2/Vs and small sub-threshold swing (SS) of 250 mV/decade upon a SiO2/Si substrate were achieved using a rational design. Moreover, small threshold voltage shifts (ΔVth) of 0.5 (−0.7) and 0.8 (−0.9) V under gate bias and light illumination stress tests were obtained. Using Si3N4/HfO2 gate dielectrics, μFE and SS were enhanced to 53.6 cm2/Vs and 75 mV/decade, respectively. Experimental observations indicate that the electrons transfer from TiO2 to a-IGZO:N2O layer resulted in the accumulation of free carriers near a-IGZO:N2O/TiO2 interfaces. Additionally, an appropriate N2O treatment reduced the oxygen-related defects and bulk/interface trap density, while controlling the carrier density in the bilayer a-IGZO:N2O/TiO2 TFTs. Furthermore, the ultra-thin TiO2 layer acted as a surface passivation layer that reduced the leakage current and protected the channel from ambient influences. The proposed high-performance hetero-structured a-IGZO:N2O/TiO2 TFTs with superior stability are expected to provide a new and effective approach to obtaining high-performance metal oxide TFTs for application in thin film electronics.

Open volume defects in ultra-thin TiO2 layers embedded in VMCO-like samples studied with positron annihilation spectroscopy

Positron annihilation signals from VMCO-like samples grown by atomic layer deposition at different temperatures are utilized for the characterization of differences in open volume defects in TiN/TiO2/a-Si heterostructures. Doppler and coincidence Doppler mode of positron annihilation spectroscopy combined with a monoenergetic positron beam were used for this study. Differences observed in the Doppler parameters indicate differences in the positron trapping states of the TiO2 epilayers grown at different temperatures. Furthermore, the coincidence-Doppler results show that these differences cannot be due to intermixing of the TiO2 and a-Si layers and formation of thin SiO2 layers at the interface during the growth process. The results indicate that the amount of open volume defects in the TiO2 layer of the VMCO-structure seems to increase with an increase in the growth temperature.

Back Cover Image

COVER CAPTION: The Back cover image is based on the Review Application of ultrathin TiO2 layers in solar energy conversion devices by Chenyu Zhou et al., https://doi.org/10.1002/ese3.1142.

Energy Science & Engineering: 10 Years of excellence

This year celebrates 10 years of the journal, Energy Science & Engineering (ESE). In 2013, ESE was launched as a peer-reviewed, open-access journal devoted to publishing high-quality research in energy. Published by Wiley and the Society of Chemical Industry (SCI), the journal offers authors a fast route to publication and the ability to share their important research in the highest visible global forum. As a prestigious journal, it maintains the highest standards of peer review as evidenced by an average rejection rate of over 60%. Dr Tomas Kaberger was the first editor-in-chief of the ESE, and he played an important leading role in the journal development. In 2018, it was my honor to succeed Tomas Kaberger as the Editor-in-Chief of the journal.1 In his inaugural editorial on the first page of this journal, Kaerger said “We hope this journal will serve as an excellent platform for integrated research, education, and communication, particularly for those with results of immediate relevance in the energy industry.”2 On the 10th birthday of ESE, we can see that ESE has grown in all possible ways, including the number of annual submissions (1000+), the number of papers (up to 300), and issues (12) published annually, and the impact factor (4.170). It has achieved numerous milestones (see Table 1) and has published many high-impact papers (see Table 2). This is because of your participation and contributions as authors, reviewers, readers, staff, editorial advisory board members, and editors. To celebrate the 10th anniversary of ESE, we organized this special issue, which consists of 12 invited articles in various energy areas, including CO2 reduction, solar energy conversion, photovoltaics, batteries, electrolysis of water, and clean fuels. The first three articles are reviews on the application of non-thermal plasma in methanol synthesis from CO2 hydrogenation, recent progress in the electrochemical reduction of carbon dioxide on metal single-atom catalysts, and CO2 reduction into formic acid under hydrothermal conditions, respectively. The fourth and fifth review articles summarized solar energy conversion, including the application of ultrathin TiO2 layers in solar energy conversion devices and the phase change of salt hydrates for photovoltaics thermal management. The review article on solid-state lithium-ion batteries constitutes the sixth article, while the seventh article is a review on sodium-ion batteries. The eighth review article assessed the degradation issues and highlighted the stabilization strategies of protonic ceramic electrolysis cells for steam electrolysis. Among four research papers, the first one is the investigation of energy management for robots. Renewable hydrogen production and natural gas blending systems were developed and assessed in the second research article, while the third research paper explored subphthalocyanine–triangulene dyads for light-harvesting device applications. The final article has made contributions to Fischer–Tropsch synthesis by converting waste to sustainable aviation fuel. I wish to express my gratitude by thanking all the authors and reviewers for their contributions to this special issue and my two colleagues (ESE Deputy Editors-in-Chief at Wiley), Dr Sonia Ojo and Dr Costas Kouroupis-Agalou, for their great efforts in the peer-review process and the organization of this special issue. At this unique moment, I would like to say “Happy Birthday” to ESE, and extend my sincere gratitude to all of you for your enthusiasm in submitting high-quality manuscripts as authors, your important evaluating manuscripts as reviewers, your energetic discussions, and helpful suggestions as editorial advisory board members, and your great contributions as handling editors. I also appreciate the strong support and help from the publisher Wiley and the SCI. Prof. Yun Hang Hu is the Editor-in-Chief of Energy Science & Engineering.

Application of ultrathin TiO2 layers in solar energy conversion devices

AbstractA vital pursuit in solar energy research is to achieve high efficiency and long‐term stability in energy conversion devices. Coating or sandwiching an ultrathin layer of TiO2 onto active solar components has been demonstrated to be a remarkably effective and facile strategy to improve their stability. The TiO2 film acts as a protection layer and enhances solar energy conversion efficiency by passivating surface recombination sites or facilitating electron transport. To date, numerous efforts have been devoted to applying ultrathin TiO2 layers in various kinds of solar energy conversion devices. In this study, we review deposition techniques, characterization methods of the resulting ultrathin TiO2 layer, as well as its applications in dye‐sensitized solar cells, organic–inorganic hybrid solar cells, and photoelectrochemical cells.

Double core-shell structure stabilized porous Si@graphene@TiO2 microsphere anode with excellent cyclability and high coulombic efficiency

The vast volume expansion of Si anode during lithiation process leads to poor cyclability and low initial coulombic efficiency (ICE), and thus seriously hampers its applications in lithium-ion batteries (LIBs). To overcome these obstacles, in this study, a double core-shell structure stabilized hierarchical porous Si (p-Si) microsphere was synthesized through a graphene-involved electrostatic self-assembly process coupled with a solvent-confined TiO2 (sc-TiO2) monomicelle assembly strategy. The advanced solvent-confined monomicelle assembly process enables the uniform deposition of ultra-thin TiO2 layer on p-Si@graphene (p-Si@G) microsphere. The G/sc-TiO2 hybrid double shell layer can significantly consolidate porous structure of p-Si microsphere and simultaneously improve the ICE value of p-Si@G@sc-TiO2 microsphere. The resulting p-Si@G@sc-TiO2 composite shows a high capacity value of 2597.9 mAh g−1 at 0.2 A g−1 with a high ICE value of 80.59%. The p-Si@G@sc-TiO2 composite also demonstrates excellent rate capability with capacity of 802.53 mAh g−1 at 8 A g−1 and outstanding cyclability with capacity retention of 68% (1005.1 mAh g−1) after 300 cycles at 2 A g−1, superior to that of p-Si, p-Si@G as well as p-Si@G@TiO2 microsphere preparing by traditional sol-gel TiO2 coating method, suggesting its promising applications in LIBs.

Improved SERS sensitivity of TiO2 nanorod films by annealing in vacuum

In this paper, substoichiometric TiO2-x nanorod films were prepared by vacuum annealing treatment of TiO2 nanorod films for an optimized period of time as a simple and effective method. As surface-enhanced Raman scattering (SERS) substrates, the TiO2-x nanorod films show good stability and high sensitivity because of the detection limit of Rhodamine 6G (R6G) as low as 10−6 M. By combining photoluminescence (PL), UV–vis diffuse reflectance, Raman and electrical measurement, a high density of electronic states related to oxygen vacancy below the Fermi level has been identified in the reduced TiO2−x. Besides, X-ray photoelectron spectroscopy (XPS) analysis exhibits an ultra-thin TiO2 layer was formed at the outmost surface of TiO2-x. The effect of the TiO2 surface layer includes two aspects: (a) providing abundant regenerated surface oxygen-vacancy-associated levels to promote charge transfer between analyte and substrate under illumination of visible light; and (b) protecting oxygen vacancy from further oxidation to improve the stability of SERS performance of TiO2.

Numerical Simulation for Optimization of Ultra-thin n-type AZO and TiO2 Based Textured p-type c-Si Heterojunction Solar Cells

A maximum efficiency of 17 % for ultra-thin n-type AZO layer and 17.5 % for ultra-thin n-type TiO2 layer based silicon heterojunction solar cell is reported by optimizing its properties which is much higher than practically obtained efficiency signifying a lot of improvements can be performed to improve efficiency of TiO2/Si and AZO/Si heterojunction solar cell. AZO layer and TiO2 layer is used as n-type emitter layer and crystalline silicon wafer is used as p-type (p-cSi) layer for modelling AZO/Si and TiO2/Si heterojunctions solar cell respectively using AFORS HET automat simulation software. Various parameters like thickness of AZO, TiO2 layer, p-cSi layer, doping concentration of donors (Nd) and effective conduction band density (Nc) are optimized. Finally, texturing at different angle is studied and maximum efficiency is reported at 70 μm thick p-type crystalline Silicon (p-cSi) wafer, that can be very helpful for manufacturing low cost HJ solar cells at industrial scale because of thin wafer and removal of additional processing setup required for deposition of amorphous silicon i-layer. Utilization of TiO2 and Aluminium doped Zinc Oxide as n-type layer and p-cSi as p-type layer can help in producing low cost and efficient heterojunction (HJ) than compared to HJ with intrinsic thin layer HIT solar cells.

Low cost copper zinc tin sulphide (CZTS) solar cells fabricated by sulphurizing sol-gel deposited precursor using 1,2-ethanedithiol (EDT)

In this paper, we report the preparation of crystalline CZTS thin films by sol–gel method followed by sulphurization using 1,2- Ethanedithiol (EDT) at 400 °C in a three zone horizontal tubular reactor equipped with computer controlled vacuum system. These films were characterized by XRD, Raman, Hall measurements and UV–Vis-NIR spectroscopy. XRD and Raman studies confirmed highly crystalline and single phase CZTS. Hall study revealed p-type semiconducting CZTS film having charge carriers density of 1.70 × 1018 cm−3 and the resistivity (ρ) of the order of 5.00 × 10−1Ω-cm. It was found that the direct band gap of 1.44 eV for CZTS film was seen from optical study. Further, double metal oxide layers having slightly different band gap were used to form a p-n junction with CZTS film. Cadmium-free solar cells with structure ITO/ZnO/CZTS/Ag (cell-1) and ITO/ZnO/com-TiO2/CZTS/Ag (cell-2) were fabricated. Electrochemical Impedance Spectroscopy (EIS) measurements were performed in the low frequency range with applied bias of 0.1 Volt for the devices. The EIS studies showed that the solar cell with ultrathin compact TiO2 layer provide a favorable path for the efficient charge transport process at the interface. The external quantum efficiency measured at 520 nm was found to be 62.5%. Cell-2 exhibited improved photovoltaic parameters with short circuit current density (Jsc) of 4.721 mA/cm2, fill factor of 0.46 and open circuit voltage (Voc) of 400 mV. The short circuit current density and fill factor of double metal oxide layers (cell-2) were increased by 78% and 46%, respectively, as compared to single metal oxide layer (cell-1).

Constructing ultrathin TiO2 protection layers via atomic layer deposition for stable lithium metal anode cycling

Uncontrollable dendrite growth during the repeated plating/stripping of Li ions induces short cycle life and safety issues, which has severely impeded the practical application of lithium metal battery. It is acknowledged that the solid electrolyte interphase (SEI) is pivotal for Li metal anode stabilization. Here, a lithium metal anode coated with an artificial SEI film as the working electrode is applied. The TiO2 coating layer is firstly demonstrated for the lithium metal anode protection via atomic layer deposition (ALD) method. Thanks to the ultrathin TiO2 layer, dendritic growth is suppressed and the cycling lifetime is significantly improved. Additionally, the thickness of TiO2 protective layer has been further optimized. Comparing with other different thickness TiO2 layer, 5 nm TiO2 layer is found to be the optimized parameter toward capacity, cycling stability and rate capability in both symmetric battery system and full-cell system. The TiO2 layer promoted uniform deposition of Li+ and effectively inhibited the growth of lithium dendrites. Symmetric Li/50TiO2||Li/50TiO2 battery could cycle stably for more than 1600 h at 1 mA cm−2, and more than 500 h at 3 mA cm−2 and 10 mA cm−2 current density. The Li/50TiO2||NCM622 full-cell exhibited better rate performance and long-cycle performance, which capacity retention was increased by 23.3% compared to bare electrode after 100 cycles at 0.5C charge-discharge current density. Furthermore, the inherent working mechanism of TiO2 artificial SEI film has been proposed. This work provides an effective and new alternative method for lithium metal anodes protection, which is critical for the future design of next-generation Li metal batteries under safe operation.

Succulent-like core–shell composite: Synthesis of CdS coated with an ultrathin layer of TiO2 and enhanced photocatalytic performance in the degradation of crystal violet and hydrogen production

A core–shell composite CdS-APS@TiO2 (APS = 3-aminopropyltriethoxysilane) has been prepared by a temperature-programmed hydrothermal method combined with a simple and convenient chemical bath deposition. The form of the product resembles that of a succulent plant. Electrostatic interaction between the water-stable TiO2 precursor with negative charge and the amino-functionalized petal-like surfaces of CdS is evident. The as-prepared composite adopts the aforementioned succulent morphology with a petal-like structure, surface-coated with TiO2. Moreover, compared with the CdS precursor, the specific surface area of the as-prepared CdS-APS@TiO2 composite is increased, and its optical absorption extends into the visible region. The CdS-APS@TiO2 composite shows high activity in multiple photocatalytic processes, and some activity in photocatalytic hydrogen production (149.2 μmol/g, 8 h). To assess its mode of action, trapping experiments have been carried out by adding various radical scavengers. Possible mechanisms for the photocatalytic degradation of dyes and the photocatalytic splitting of water over the CdS-APS@TiO2 composite are proposed.

Enhanced photoresponse of TiO2/MoS2 heterostructure phototransistors by the coupling of interface charge transfer and photogating

Two-dimensional (2D) MoS2 with appealing physical properties is a promising candidate for next-generation electronic and optoelectronic devices, where the ultrathin MoS2 is usually laid on or gated by a dielectric oxide layer. The oxide/MoS2 interfaces widely existing in these devices have significant impacts on the carrier transport of the MoS2 channel by diverse interface interactions. Artificial design of the oxide/MoS2 interfaces would provide an effective way to break through the performance limit of the 2D devices but has yet been well explored. Here, we report a high-performance MoS2-based phototransistor with an enhanced photoresponse by interfacing few-layer MoS2 with an ultrathin TiO2 layer. The TiO2 is deposited on MoS2 through the oxidation of an e-beam-evaporated ultrathin Ti layer. Upon a visible-light illumination, the fabricated TiO2/MoS2 phototransistor exhibits a responsivity of up to 2,199 A/W at a gate voltage of 60 V and a detectivity of up to 1.67 × 1013 Jones at a zero-gate voltage under a power density of 23.2 µW/mm2. These values are 4.0 and 4.2 times those of the pure MoS2 phototransistor. The significantly enhanced photoresponse of TiO2/MoS2 device can be attributed to both interface charge transfer and photogating effects. Our results not only provide valuable insights into the interactions at TiO2/MoS2 interface, but also may inspire new approach to develop other novel optoelectronic devices based on 2D layered materials.

High-efficiency polymer solar cells controlled by photoelectrochemically formed ordered polythiophene active layers with various thicknesses

The effect of polythiophene (PT) with various thicknesses on photocurrent generation was investigated. The PT layer was prepared via anchor-guided photoelectrochemical polymerization of thiophene onto TiO2 layers (0.25–6 μm-thick) covered with a sub-monolayer of tethered C207 molecules, 3-{5-[N,N-Bis(4-diphenylamino)pheny]thieno[3,2-b]thiophen-2-yl}-2-cyano-acrylate acid. Although the thickness of the porous TiO2 layer is different from the ultra-thin compact TiO2 layer (150 nm), a highly ordered and uniform PT layer can also be photoelectrochemically grown onto the surface of and into the crevices of the C207-covered TiO2 nanoparticles. With a 1.5 μm-thick PT layer separated from the cathode by the hole-transport material Spiro-OMeTAD, 2,2′,7,7′-tetrakis(N,N-di(4-methoxyphenyl)amino)-9,9′-spirobifluorene, the open-circuit voltage Voc and short-circuit current density Jsc were measured to be 0.78 ± 0.02 V and 14.77 ± 0.31 mA/cm2, respectively. The power conversion efficiency (8.41 ± 0.31 %) of such a polythiophene-based solar cell (PTSC) is higher than those of solar cells sensitized by an ordered thin PT film (270 nm) grown onto compact TiO2 layers or by a thick PT layer grown onto coarse TiO2 layers (6 μm). The high conversion efficiency of the PTSC is attributed to the oriented PT growth along the chain-like C207 molecules at the TiO2 nanoparticles, which facilitates facile transport of charges while effectively preventing the hole/electron recombination.

Surface Modification of Fe7 S8 /C Anode via Ultrathin Amorphous TiO2 Layer for Enhanced Sodium Storage Performance.

Iron sulfides with high theoretical capacity and low cost have attracted extensive attention as anode materials for sodium ion batteries. However, the inferior electrical conductivity and devastating volume change and interface instability have largely hindered their practical electrochemical properties. Here, ultrathin amorphous TiO2 layer is constructed on the surface of a metal-organic framework derived porous Fe7 S8 /C electrode via a facile atomic layer deposition strategy. By virtue of the porous structure and enhanced conductivity of the Fe7 S8 /C, the electroactive TiO2 layer is expected to effectively improve the electrode interface stability and structure integrity of the electrode. As a result, the TiO2 -modified Fe7 S8 /C anode exhibits significant performance improvement for sodium-ion batteries. The optimal TiO2 -modified Fe7 S8 /C electrode delivers reversible capacity of 423.3 mA h g-1 after 200 cycles with high capacity retention of 75.3% at 0.2 C. Meanwhile, the TiO2 coating is conducive to construct favorable solid electrolyte interphase, leading to much enhanced initial Coulombic efficiency from 66.9% to 72.3%. The remarkable improvement suggests that the interphase modification holds great promise for high-performance metal sulfide-based anode materials for sodium-ion batteries.

Electrosprayed MnO2 on ZnO nanorods with atomic layer deposited TiO2 layer for photoelectrocatalytic water splitting

We have designed and produced a hierarchical photocatalyst for water splitting by first fabricating ZnO nanorods via a chemical bath deposition (CBD) process using ZnO seeds electrosprayed onto In-doped tin oxide (ITO), then electrospraying MnO2 particles as a co-catalyst, and finally depositing an ultrathin passivation layer of TiO2 via atomic layer deposition. These hierarchical photocatalysts exhibit excellent photoelectrochemical properties and reduced photocorrosion compared to materials without TiO2 coating. Moreover, the MnO2-garnished ZnO nanorods obtained at 550 °C deliver a 1.7-fold enhancement in photocurrent density (0.95 mA/cm2) at 1.2 VAg/AgCl in 0.5-M Na2SO3 solution compared to ZnO nanorods without MnO2. We attribute improved photocurrent density to rapid charge transfer and charge separation at the ZnO–MnO2 interface. This investigation illustrates a balanced design of a nanoarchitecture for photoelectrodes that favors formation of effective photoelectrocatalytic sites while improving stability for potential large-scale water splitting applications.

Performance enhancement of perovskite solar cells via modification of the TiO2/perovskite interface with oxygen plasma treatment

High-temperature (~500 °C) sintering is a routine post-treatment to fabricate compact Titanium dioxide (TiO2) electron selective layer (ESL) in high-performance perovskite solar cells (PSCs). Here, we propose an effective low-temperature (<150°C) approach: pinhole-free and compact ultrathin TiO2 layers are fabricated via thermal atomic layer deposition (ALD) following a low-pressure oxygen plasma treatment. The hydrophilicity of TiO2 surfaces can be suitably tailored, which favors precursor solution being well spread and the growth of perovskite film. In addition, effective removal of oxygen vacancies serving as unproductive quenching sites in TiO2 surface is observed, which is attributed to atomic oxygen radical, the most reactive species generated in oxygen plasma. The PSC device with oxygen-plasma-treated ALD–TiO2 ESL achieves an efficiency of 14.9%, which is better than 13.3% of the device with 500 °C- sintered ALD–TiO2 ESL and comparable to 14.3% of the device with conventional 500°C-sintered Sol–gel–TiO2 ESL under our conditions.

Adapting Aluminum-Doped Zinc Oxide for Electrically Conductive Membranes Fabricated by Atomic Layer Deposition.

The use of electrically conductive membranes has recently drawn great interest in water treatment as an approach to reduce biofouling. Most conductive membranes are made by binding nanoparticles (carbon nanotubes or graphene) to a polymeric membrane using additional polymers, but this method risks leaching these nanomaterials into the environment. A new approach was developed here based on producing an electrically conductive layer of aluminum-doped zinc oxide (AZO) by atomic layer deposition. The aqueous instability of AZO, which is a critical challenge for water applications, was solved by capping the AZO layer with an ultrathin (∼11 nm) TiO2 layer (AZO/TiO2). The combined film exhibited prolonged stability in water and had a low sheet resistance of 67 Ω/sq with a 120 nm-thick coating, while the noncapped AZO coating quickly deteriorated as shown by a large increase in membrane resistance. The AZO/TiO2 membranes had enhanced resistance to biofouling, with a 72% reduction in bacterial counts in the absence of an applied current due to its higher hydrophilicity than the bare polymeric membrane, and it achieved an additional 50% reduction in bacterial colonization with an applied voltage. The use of TiO2-capped AZO layers provides a new approach for producing conductive membranes using abundant materials, and it avoids the risk of releasing nanoparticles into the environment.

Sol–gel approach for the growth of vertically aligned 3D-TiO2 nanorod arrays as an efficient photoanode for high-performance dye-sensitized solar cells

In this study, a facile, low cost, and scalable sol–gel method has been proposed for the coating of ultra-thin layer of TiO2 on FTO substrate as a seed layer for the growth of 3D-TiO2 nanorod (3D-TiO2-NR) arrays on FTO. Then, the two-step hydrothermal process including nanorod growth and the chemical etching treatment was proceeded for the fabrication of FTO/3D-TiO2-NR photoanodes. The thickness of the deposited TiO2 in FTO/TiO2-sg samples was measured with small-angle X-ray scattering technique, and it was obtained to be 21.3 nm. FE-SEM and TEM techniques were used for the morphological characterization of 3D-TiO2-NR, and it was obtained that the tightly adhered film of vertically aligned 3D-TiO2-NR with two-layer nanostructuring is formed with a cubic base and a nanorods head. Finally, DSSCs with iodine-based and cobalt(II/III) tris(2,2′-bipyridine) complex-based electrolytes with two different photoanodes including 3D-TiO2-NR and TiO2-NP were assembled and their photovoltaic characteristics were investigated. For [Co(bpy)3]2+/3+ shuttle-based DSSC, the obtained power conversion efficiency (η) was about 3.5% with Jsc of 9.36 mA cm−2 in 3D-TiO2-NR-based DSSC, while η of TiO2-NP-based DSSC was about 1.4%. The results showed that employing 3D-TiO2-NR-based photoanode in DSSCs with bulky electron shuttles remarkably improves the photovoltaic characteristics of DSSCs. Electrochemical impedance spectroscopic studies also showed the lower charge transfer resistances for DSSCs with nanorod-based photoanode building blocks.

Z-scheme Bi2O2.33/Bi2S3 heterojunction nanostructures for photocatalytic overall water splitting

Photocatalysts with a wide response to solar spectrum especially to visible light are supposed to have a high energy conversion efficiency in solar water splitting. Heterogeneous binary composite photocatalysts exhibit outstanding performance in solar light absorption and photocarrier transfer/transport. In this work, a Z-scheme photocatalyst based on Bi2O2.33/Bi2S3 heterojunction is successfully designed and fabricated by assembling Bi2S3 nanoneedles on Bi2O2.33 nanosheets. Benefiting from the effective light absorption of Bi2S3 to solar light and the facilitated charge transfer by the Z-scheme band structure of Bi2O2.33/Bi2S3, the composite photocatalyst exhibits a fascinating photocatalytic performance in water splitting. With the help of Pt as a co-catalyst and sacrificial agent, the production rate of H2 can reach 62.61 μmol·h−1 (sample area 2 cm2). The direct Z-scheme junction also exhibits the capacity of overall water splitting. Moreover, the stability of the heterojunction photocatalyst is optimized by depositing an ultra-thin amorphous TiO2 layer (about 3 nm) to avoid photocorrosion of Bi2S3. This work will provide a new insight into the design and development of efficient and long-life photocatalysts.