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Angstrom Thick ZnO Passivation Layer to Improve the Photoelectrochemical Water Splitting Performance of a TiO2 Nanowire Photoanode: The Role of Deposition Temperature
摘要： In this paper, we demonstrate that angstrom thick single atomic layer deposited (ALD) ZnO passivation can significantly improve the photoelectrochemical (PEC) activity of hydrothermally grown TiO2 NWs. It is found that this ultrathin ZnO coating can passivate the TiO2 surface defect states without hampering the carrier’s transfer dynamics. Moreover, a substantial improvement can be acquired by changing the deposition temperature of the ZnO layer (80 °C, and 250 °C) and named as 80 °C TiO2-ZnO, and 250 °C TiO2-ZnO. It was found that the deposition of this single layer in lower temperatures can lead to higher PEC activity compared to that deposited in higher ones. As a result of our PEC characterizations, it is proved that photoconversion efficiency of bare TiO2 NWs can be improved by a factor of 1.5 upon coating it with a single ZnO layer at 80 °C. Moreover, considering the fact that this layer is a passivating coating rather than a continuous layer, it also keeps the PEC stability of the design while this feature cannot be obtained in a thick shell layer case. This paper proposes a bottom up approach to control the electron transfer dynamics in a heterojunction design and it can be applied to other metal oxide combinations.
关键词： deposition temperature,atomic layer deposition,photoelectrochemical water splitting,ZnO passivation,TiO2 nanowire
更新于2025-09-23 15:21:01
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Enhanced current density of anatase TiO2 nanowire arrays by interface connection modulation in flexible quantum dot sensitized solar cells
摘要： The stability and photovoltaic conversion efficiency are very important issues for the industry application of flexible solar cells, which have been seriously limited by the interface connection of basic photo-electrodes in solar cells. Here, one-dimensional TiO2 nanowire arrays films were employed as photo-electrodes of flexible solar cells, which have modulated interface connection of the photo-electrodes by introducing small size of nanoparticles and heating pressure process. The charge generation and separation properties of photo-electrodes have been influenced, which may be attributed by the changes on band energy of small size of nanoparticles in photo-electrodes. With the improvement on the interface connection in the photo-electrodes, the charge transfer property has been effectively improved, which have exhibited a higher current density value of the solar cells, achieving photovoltaic conversion efficiency enhancement from 2.55% to 3.90%. Moreover, there have no obvious changes on the photovoltaic conversion efficiency of these flexible QDSSCs solar cells under the curling condition.
关键词： Anatase TiO2 nanowire arrays,Flexible quantum dot sensitized solar cell,Interface connection,Photovoltaic performance enhancement,Small size of nanoparticles,Heating pressure
更新于2025-09-23 15:19:57
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European Microscopy Congress 2016: Proceedings || Defects in as-grown vs. annealed rutile titania nanowires and their effect on properties
摘要： Semiconducting metal oxides play a key role in electrochemical and photo physical applications like photo catalysis and as electrode material in solar cells and Li-ion batteries. Among these metal oxides, hydrothermally grown rutile TiO2 nanowire arrays are promising as the 1 D structure possesses a large surface area and a directed electron path towards the substrate. However, the efficiency of these devices is also influenced by the defects inside the nanowires (dislocations, stacking faults, titanium interstitials and oxygen vacancies). A previous study showed that as-grown nanowires have a high density of lattice defects.[1] However, these defects can be removed by an additional annealing step. Latest findings demonstrate that hybrid solar cells where those annealed nanowires are incorporated have significantly higher power-conversion efficiency.[2] However, the removal of the defects is not fully understood so far. In our present work, transmission electron microscopy (TEM) was used to study the changes within the nanowire during annealing. TEM investigations were performed at 200 kV using a JEOL JEM-2200FS and at 300 kV using a FEI Titan Themis 60-300. First results were obtained by ex-situ TEM analysis of as-grown TiO2 nanowires and nanowires, which were annealed at 500 °C for 4 h. These ex-situ analysis confirm that both, as-grown and annealed nanowires, have the rutile crystal structure. Defects, present in the as-grown state, can be removed by the thermal treatment. Concurrently, a structural transformation inside the nanowires occurs resulting in faceted voids of several nanometer in diameter. Using tilt series from -70° to +70° in high-angle annular dark-field (HAADF) scanning (S)TEM mode and the discrete iterative reconstruction technique (DIRT)[3], a TEM tomograph was obtained, which proved that these voids are solely formed inside the nanowire and not at the nanowire surface (Fig. 1). Further analysis including electron energy loss spectroscopy revealed changes of the oxidation state at the surface region of the voids during annealing, whereas the rutile TiO2 crystal structure was maintained. HAADF-STEM in-situ heating experiments, performed in a JEOL JEM-2200FS with a DENSsolutions heating holder, enabled the direct observation of the structural changes inside the rutile TiO2 nanowires (Fig. 2). Using a slow heating ramp of 3.3°C/min, a sudden formation of these voids at around 500 °C could be observed. Heating at lower temperatures did not affect the structure of the nanowire and also an additional heating after the transformation (600°C, 1h) did not change the size and shape of the voids. These ex-situ and in-situ observations are a decisive step to explain the mechanisms involved in this process in more detail. The results of our TEM investigation were correlated to the properties of as-grown and annealed TiO2 nanowires. Here, we could show that the healing of the lattice defects upon annealing not only increased the performance of hybrid solar cells but also affects other properties of the nanowires e.g. chemical stability.
关键词： in-situ TEM,TiO2 nanowire,defect healing
更新于2025-09-16 10:30:52
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A 3D hybrid nanowire/microcuboid optoelectronic electrode for maximised light harvesting in perovskite solar cells
摘要： A high-performance optoelectronic device requires efficient light harvesting and management in the electrodes. In this work, we report the integration of antireflective anatase TiO2 nanowire (TNW) arrays and CH3NH3PbI3 microcuboid (CMC) film into a new bilayer architecture. The highly porous and well-interconnected anatase TNW arrays showcase antireflective properties for enhanced light transmittance and provide a largely accessible surface area for anchoring the perovskite light absorber. The thick and compact CMC film enables efficient light absorption. Thus, perovskite solar cells (PSCs) fabricated with a hybrid TNW/CMC optoelectronic electrode achieved an optimal power conversion efficiency (PCE) of up to 20.1% under one sun illumination with a high Jsc of 23.2 mA cm?2, which can be attributed to the maximised light harvesting efficiency within the devices.
关键词： light harvesting,perovskite solar cells,CH3NH3PbI3 microcuboid,optoelectronic electrode,TiO2 nanowire
更新于2025-09-11 14:15:04
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Quantum confinement chemistry of CdS QDs plus hot electron of Au over TiO2 nanowire protruding to be encouraging photocatalyst towards nitrophenol conversion and ciprofloxacin degradation
摘要： Solar light harvesting science is ascertained to be the topmost effective green technique in alleviating environmental pollutants. In this respect, we report a visible light active TiO2/Au/CdS QDs nanocomposite which manifested upgraded photocatalytic activity towards the transformation of 2-nitrophenol, 4-nitrophenol, and degradation of ciprofloxacin. Here, TiO2 nanowire is synthesized by a molten flux method with high product yield and crystallinity with organized dimensions. Au nanoparticles are successfully integrated in between TiO2-CdS composite by Reverse Turkevich method. The prepared composites are meticulously characterized by different physical and optoelectronic techniques to inspect the crystal structure, phase purity, optical properties, nanostructured morphology and electrochemical properties. The plasmonic direct hot electron transfer (DET) mechanism is confirmed from UV-Vis DRS spectra. The prepared composite produces 2.98 mA/cm2 of current density under light irradiation. A Longer lifetime of electrons is found from Bode phase plot i.e. 97.4 μs for TiO2/1%Au/3%CdS QDs owing to the integrative cooperation effect of high aspect ratio of TiO2 nanowire, quantum size effect of CdS and the direct hot electron transfer by Au nanoparticle.
关键词： TiO2 nanowire,2-nitrophenol,DET,4-nitrophenol,ciprofloxacin,CdS QDs
更新于2025-09-09 09:28:46