ABSTRACT
Recent progress in two-dimensional ferroelectrics greatly expands the versatility and tunability in van der Waals heterostructure based electronics. However, the switching endurance issue that widely plagues conventional ferroelectrics in practical applications is hitherto unexplored for van der Waals layered ferroelectrics. Herein, we report the observation of unusual polarization fatigue behaviors in van der Waals layered CuInP2S6, which also possesses finite ionic conductivity at room temperature. The strong intertwinement of the short-range polarization switching and long-range ionic movement in conjunction with the van der Waals layered structure gives rise to unique morphological and polarization evolutions under repetitive electric cycles. With the help of concerted chemical, structural, lattice vibrational and dielectric analyses, we unravel the critical role of the synergy of ionic migration and surface oxidation on the anomalous polarization enhancement and the eventual polarization degradation. This work provides a general insight into the polarization fatigue characteristics in ionically-active van der Waals ferroelectrics and delivers potential solutions for the realization of fatigue-free capacitors.
ABSTRACT
Solar desalination of seawater is an effective approach to address the scarcity of freshwater resources. For solar steam generation, it is critical to design biodegradable, sustainable, low-cost, and high-evaporation-rate technology. This study aims to develop a novel solar desalination technology by designing and fabricating a nanocomposite material with excellent light absorption and thermal conversion properties. We designed a double-layer aerogel structure, which uses naturally abundant carboxymethyl cellulose (CMC) as the basic skeleton to achieve sustainability and biodegradability, and uses carbon nanotubes as the photothermal material for efficient light absorption to prepare a ferric tannate/carbon nanotube/carboxymethyl cellulose composite aerogel (FT-CNT-CMC aerogel). Experimental results demonstrate that the FT-CNT-CMC aerogel exhibits a high light absorption rate of 96-98% within the spectral range of 250-2400 nm, showcasing remarkable photothermal conversion performance. Under a sun intensity of 1 kW·m-2, the FT-CNT-CMC aerogel achieves a significant evaporation rate of 1.942 kg·m-2·h-1 at room temperature. Moreover, the excellent performance of the FT-CNT-CMC aerogel is validated in practical seawater desalination and organic dye wastewater purification. The FT-CNT-CMC aerogel exhibits a retention rate exceeding 99% for Na+, Mg2+, K+, and Ca2+ ions in simulated seawater, while no characteristic absorption peaks are observed in methylene blue and rhodamine B dye solutions after purification. These findings highlight the promising potential of the FT-CNT-CMC aerogel in the field of novel solar desalination, providing a viable solution to obtain freshwater.
ABSTRACT
Fog-harvesting performance is influenced by surface wettability, patterned structure and the heat transfer coefficient. In this work, we have prepared different surfaces with a stripe array of superhydrophilic, superslippery and superslippery/superhydrophilic surfaces for fog harvesting on silicon substrates using photolithography and silver-assisted chemical etching. The surface wettability and heat transfer coefficients of the above samples have been investigated. We analyzed the contact angle, sliding angle and transport state of droplets on these surfaces. The fog-harvesting rate of all samples under different voltages of the cooling pad (V = 0, 2.0, 2.5, 3.0, 3.5 V) was measured. Results showed that the superslippery/superhydrophilic striped surface could achieve rapid droplet nucleation, directional transport and efficient collection due to its superhydrophilic striated channels and the Laplace pressure difference between different wettability regions. At a condensation voltage of 3.5 V, the fog-harvesting rate efficiencies of the uniformly striped superhydrophilic and superslippery surface were 1351 mg·cm-2·h-1 and 1265 mg·cm-2·h-1, respectively, while the fog-harvesting rate of the superslippery/superhydrophilic striped surface was 1748 mg·cm-2·h-1. Compared with the original silicon surface, the maximum fog-harvesting rate of the superslippery/superhydrophilic striped surface was improved by 86.9%. This study offers significant insights into the impact of heat transfer and silicon surface wettability on the process of fog collection.
ABSTRACT
Transition metal thiophosphate, CuInP2S6 (CIPS), has recently emerged as a potentially promising material for photoelectrochemical (PEC) water splitting due to its intrinsic ferroelectric polarization for spontaneous photocarrier separation. However, the poor kinetics of the hydrogen evolution reaction (HER) greatly limits its practical applications. Herein, we report self-enhancing photocatalytic behavior of a CIPS photocathode due to chemically driven oxygen incorporation by photoassisted acid oxidation. The optimal oxygen-doped CIPS demonstrates a >1 order of magnitude enhancement in the photocurrent density compared to that of pristine CIPS. Through comprehensive spectroscopic and microscopic investigations combined with theoretical calculations, we disclose that oxygen doping will lower the Fermi level position and decrease the HER barrier, which further accelerates charge separation and improves the HER activity. This work may deliver a universal and facile strategy for improving the PEC performance of other van der Waals metal thiophosphates.
ABSTRACT
Recently, large-scale photonic integrated circuits have seen rapid development. Optical switches are the elementary units used to realize optical routers and processors. However, the high static power and large footprint of silicon electro-optic and thermo-optic switches are becoming an obstacle for further scaling and high-density integration. In this Letter, we demonstrate a 2×2 nonvolatile silicon Mach-Zehnder optical switch enabled by low-loss phase change material Sb2S3. Changing the phase state of Sb2S3 can switch the optical transmission between the bar and cross paths. As no static power is required to maintain the phase state, it can find promising applications in optical switch matrices and reconfigurable optical circuits.
ABSTRACT
Black silicon contains high-aspect-ratio micro/nanostructures with greatly suppressed front-surface reflection, thus possessing superior property in photoelectric devices. In this report, by a two-step copper-assisted chemical etching method, we have fabricated pyramid n+p-black silicon with optimized morphology and anti-reflectance capability, through systematically tuning the concentration of both copper ions and reducing agents, as well as the etching time. The improved optical absorption and superior charge transfer kinetics validate n+p-black silicon as a highly active photocathode in photoelectrochemical cells. The onset potential of 0.21â V vs. RHE and the saturation photocurrent density of 32.56â mA/cm2 are achieved in the optimal n+p-black silicon. In addition, the nanoporous structure with lower reflectance is also achieved in planar p-silicon via the same etching method. Moreover, the photodetectors based on planar p-black silicon show significantly enhanced photoresponsivity over a broad spectral range. This study offers a low-cost and scalable strategy to improve the photoelectric-conversion efficiency in silicon-based devices.
ABSTRACT
Visible-light-active ferroelectric materials are gaining increasing attention due to the unique ferroelectric photovoltaic effect. To boost the light harvesting capability, vast research is devoted to band gap engineering by chemical substitutions, regardless of the side effect on ferroelectric polarization. Here, we focus on how polar order affects the optical and photovoltaic properties. Using BiFeO3as the model system, we induce the polarization rotation by A-site La substitution, which results in continuous reduction of optical anisotropy of the samples, as revealed by the concerted optical characterizations. This further causes the decrease of angular dependence of ferroelectric photovoltaic effect on the light polarization. The results demonstrate the inner connection of the ferroelectric polarization and optical anisotropy via the lattice degree of freedom.
ABSTRACT
p-Type compounds Cu2BaSnS4 (CBTS) are extremely attractive materials for photocathode applications because of their suitable conduction and valence bands, earth-abundant sources, and environmental friendly nature. Herein, an inexpensive and reproducible aqueous solution approach has been developed to synthesize CBTS films with single-crystalline grains as large as micron scale. Because of the large crystalline grains, the as-grown CBTS films show excellent carrier mobility (1.29 cm2/V·s). Greater than 4 mA·cm-2 photocurrent density has been obtained in a neutral solution for bare Mo/CBTS film photocathodes under 100 mW·cm-2 illumination at 0 V versus reversible hydrogen electrode.
ABSTRACT
In this work, thin SiO2 insulating layers were generated on the top and bottom surfaces of single-crystalline silicon plates (n type) by thermal oxidation to obtain an insulator/semiconductor/insulator (ISI) multilayer structure. X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) pictures implied that all of the synthesized SiO2 layers were amorphous. By controlling the thermal oxidation times, we obtained SiO2 layers with various thicknesses. The dielectric properties of silicon plates with different thicknesses of SiO2 layers (different thermal oxidation times) were measured. The dielectric properties of all of the single-crystalline silicon plates improved greatly after thermal oxidation. The dielectric constant of the silicon plates with SiO2 layers was approximately 104, which was approximately three orders more than that of the intrinsic single-crystalline silicon plate (11.9). Furthermore, both high permittivity and low dielectric loss (0.02) were simultaneously achieved in the single-crystalline silicon plates after thermal oxidation (ISI structure).
ABSTRACT
A porous carbon layer was inserted between a BiFeO3 film and a Pt catalyst for efficient solar water splitting. A photocathodic current density of -235.4 µA cm-2 at 0 V versus RHE and an onset potential of 1.19 V versus RHE were obtained under 100 mW cm-2 Xe-lamp illumination.
ABSTRACT
Water splitting in a photoelectrochemical cell, which converts sunlight into hydrogen energy, has recently received intense research. Silicon is suitable as a viable light-harvesting material for constructing such cell; however, there is a need to improve its stability and explore a cheap and efficient cocatalyst. Here we fabricate highly efficient and stable photocathodes by integrating crystalline MoS2 catalyst with â¼2 nm Al2O3 protected n+p-Si. Al2O3 acts as a protective and passivative layer of the Si surface, while the sputtering method using a MoS2 target along with a postannealing leads to a vertically standing, conformal, and crystalline nano-MoS2 layer on Al2O3/n+p-Si photocathode. Efficient (0.4 V vs RHE onset potential and 35.6 mA/cm2 saturated photocurrent measured under 100 mA/cm2 Xe lamp illumination) and stable (above 120 h continuous water splitting) photocathode was obtained, which opens the door for the MoS2 catalyst to be applied in photoelectrochemical hydrogen evolution in a facile and scalable way.
ABSTRACT
Pb(Zr(0.2)Ti(0.8))O3 wrapped CaFe2O4 particles were constructed on ITO coated quartz as a photocathode for efficient water splitting. A photocurrent of 152 µA cm(-2) was obtained under zero bias vs. Ag/AgCl and 100 mW cm(-2) with the assistance of positive poling and Ag decoration.
ABSTRACT
PZT film of 300 nm thickness was deposited on tin indium oxide (ITO) coated quartz by a sol-gel method. Four metal electrodes, such as Pt, Au, Cu and Ag, were used as top electrodes deposited on the same PZT film by sputtering at room temperature. In ITO-PZT-Ag and ITO-PZT-Au structures, the visible light (400-700 nm) can be absorbed partially by a PZT film, and the maximum efficiency of photoelectric conversion of the ITO-PZT-Ag structure was enhanced to 0.42% (100 mW cm(-2), AM 1.5G), which is about 15 times higher than that of the ITO-PZT-Pt structure. Numerical simulations show that the natural random roughness of polycrystalline-PZT-metal interface can offer a possibility of coupling between the incident photons and SPs at the metal surface. The coincidence between the calculated SP properties and the measured EQE spectra reveals the SP origin of the photovoltaic enhancement in these ITO-PZT-metal structures, and the improved photocurrent output is caused by the enhanced optical absorption in the PZT region near the metal surface, rather than by the direct charge-transfer process between two materials.
ABSTRACT
ITO/Pb(Zr,Ti)O(3) contacts and Ag nanoparticles were used to construct a novel ferroelectric film photocathode exhibiting a stable short-circuit photocurrent of 110 µA cm(-2) and an open-circuit voltage of 0.76 V under 100 mW cm(-2) Xe-lamp illumination and zero-bias versus SCE.
ABSTRACT
Because of the existence of interface Schottky barriers and depolarization electric field, ferroelectric films sandwiched between top and bottom electrodes are strongly expected to be used as a new kind of solar cells. However, the photocurrent with a typical order of µA/cm(2) is too low to be practical. Here we demonstrate that the insertion of an n-type cuprous oxide (Cu(2)O) layer between the Pb(Zr,Ti)O(3) (PZT) film and the cathode Pt contact in a ITO/PZT/Pt cell leads to the short-circuit photocurrent increasing 120-fold to 4.80 mA/cm(2) and power conversion efficiency increasing of 72-fold to 0.57% under AM1.5G (100 mW/cm(2)) illumination. Ultraviolet photoemission spectroscopy and dark J-V characteristic show an ohmic contact on Pt/Cu(2)O, an n(+)-n heterojunction on Cu(2)O/PZT and a Schottky barrier on PZT/ITO, which provide a favorable energy level alignment for efficient electron-extraction on the cathode. Our work opens up a promising new method that has the potential for fulfilling cost-effective ferroelectric-film photovoltaic.
Subject(s)
Copper/chemistry , Electric Power Supplies , Electrodes , Nanostructures/chemistry , Nanostructures/ultrastructure , Semiconductors , Solar Energy , Energy Transfer , Equipment Design , Equipment Failure Analysis , Magnetic FieldsABSTRACT
A novel nanostructured ferroelectric photovoltaic material, consisting of the ferroelectric lead zirconate titanate (PZT) film and Ag(2) O semiconductor nanoparticles of comparatively narrow bandgap, has demonstrated a remarkable enhancement in the photovoltaic effects and the highest light-electricity conversion efficiency among those PZT-based photodiodes previously reported. This work sheds light on the design and enhanced performance of new optoelectronic and solar energy devices.
