Successive Ionic Layer Absorption And Reaction Research Articles

Doubling the power conversion efficiency in CdS/CdSe quantum dot sensitized solar cells with a ZnSe passivation layer

The surface passivation layer in quantum dot sensitized solar cells (QDSSCs) plays a very important role in preventing surface charge recombination and, thus, improving the power conversion efficiency. The present study demonstrated the introduction of a ZnSe passivation layer prepared with a successive ionic layer absorption and reaction (SILAR) method in CdS/CdSe co-sensitized solar cells, though not likely in the ideal form of a conformal overlayer, have significantly enhanced the power conversion efficiency, which was found to be far more efficient than the most widely used ZnS passivation layer. Not only can the ZnSe passivation layer reduce surface charge recombination, but can also enhance the light harvesting. The short-circuit current density, open-circuit voltage, fill factor, and the corresponding photovoltaic conversion efficiency were all significantly improved with the introduction of a ZnSe passivation layer but varied appreciably with the layer thickness. When three SILAR cycle layer was applied, the power conversion efficiency is as high as 6.4%, which is almost doubled the efficiency of 3.4% for the solar cell without ZnSe passivation layer. For the comparison, the CdS/CdSe co-sensitized solar cells with optimum ZnS passivation layer was also fabricated, which generated a power conversion efficiency of 4.9%, much lower than 6.4% of ZnSe passivated QDSSCs. This work demonstrated that ZnSe would be a good alternative to ZnS as a passivation material.

Instrument-Free Synthesizable Fabrication of Label-Free Optical Biosensing Paper Strips for the Early Detection of Infectious Keratoconjunctivitides.

We introduce a surface-enhanced Raman scattering (SERS)-functionalized, gold nanoparticle (GNP)-deposited paper strip capable of label-free biofluid sensing for the early detection of infectious eye diseases. The GNP biosensing paper strip was fabricated by the direct synthesis and deposition of GNPs on wax-divided hydrophilic areas of a permeable porous substrate through a facile, power-free synthesizable, and highly reproducible successive ionic layer absorption and reaction (SILAR) technique. To maximize localized surface plasmon resonance-generated SERS activity, the concentration of the reactive solution and number of SILAR cycles were optimized by controlling the size and gap distance of GNPs and verified by computational modeling with geometrical hypotheses of Gaussian-estimated metallic nanoparticles. The responses of our SERS-functionalized GNP paper strip to Raman intensities exhibited an enhancement factor of 7.8 × 10(8), high reproducibility (relative standard deviation of 7.5%), and 1 pM 2-naphthalenethiol highly sensitive detection limit with a correlation coefficient of 0.99, achieved by optimized SILAR conditions including a 10/10 mM/mM HAuCl4/NaBH4 concentration and six SILAR cycles. The SERS-functionalized GNP paper is supported by a multivariate statistics-preprocessed machine learning-judged bioclassification system to provide excellent label-free chemical structure sensitivity for identifying infectious keratoconjunctivitis. The power-free synthesizable fabrication, label-free, rapid analysis, and high sensitivity feature of the SILAR-fabricated SERS-functionalized GNP biosensing paper strip makes it an excellent alternative in point-of-care applications for the early detection of various infectious diseases.

Enhanced photocatalytic and photoelectrochemical properties of TiO2 nanorod arrays sensitized with CdS nanoplates

TiO2 nanorod arrays (NRAs) sensitized with CdS nanoplates (NPLs) were fabricated via a two-step method. Vertically aligned TiO2 NRAs were synthesized by a hydrothermal method, and followed by depositing CdS NPLs on TiO2 NRAs via successive ion layer absorption and reaction (SILAR) method. Their surface morphology, structure, photoelectrochemical, and photocatalytic properties were investigated. UV-via absorption spectra suggest that the absorption peaks shift from the ultraviolet region (408nm) to the visible region (580nm) when compared to pure TiO2 nanorod arrays. Additionally, upon irradiation of visible light, the photocurrent response of CdS NPL sensitized TiO2 NRAs after 8 SILAR cycles significantly improved, displaying an optimal photocurrent density of 168.5μA/cm2, which is much higher than that of the unsensitized samples (48.1μA/cm2). They also exhibited excellent photocatalytic properties where the degradation rate of methyl orange under visible light showed an enhancement of 92.4% compared to bare TiO2 NRAs. The mechanisms of the enhanced photocatalytic and photoelectrochemical properties of TiO2 nanorod arrays sensitized with CdS nanoplates are discussed in detail.

Spectral Dependent Photoelectrochemical Behaviors of CdS Sensitized ZnO Nanorods.

CdS decorated ZnO nanorods have been grown by a combination of hydrothermal method and successive ion layer absorption and reaction (SILAR) method. Optical absorption and emission properties of ZnO nanorods have been studied after sensitization with CdS nanoparticles. Current-voltage characteristics of ZnO nanorods and CdS sensitized ZnO nanorods have been studied in an electrochemical cell. The spectral dependent photocurrent and photopotential behaviors of ZnO nanorods and CdS sensitized ZnO nanorods have been investigated using monochromatic light of wavelength 300-700 nm. The photopotential recovery time have been estimated for CdS sensitized nanorods and pristine nanorods.

Enhanced Performance of PbS-quantum-dot-sensitized Solar Cells via Optimizing Precursor Solution and Electrolytes.

This work reports a PbS-quantum-dot-sensitized solar cell (QDSC) with power conversion efficiency (PCE) of 4%. PbS quantum dots (QDs) were grown on mesoporous TiO2 film using a successive ion layer absorption and reaction (SILAR) method. The growth of QDs was found to be profoundly affected by the concentration of the precursor solution. At low concentrations, the rate-limiting factor of the crystal growth was the adsorption of the precursor ions, and the surface growth of the crystal became the limiting factor in the high concentration solution. The optimal concentration of precursor solution with respect to the quantity and size of synthesized QDs was 0.06 M. To further increase the performance of QDSCs, the 30% deionized water of polysulfide electrolyte was replaced with methanol to improve the wettability and permeability of electrolytes in the TiO2 film, which accelerated the redox couple diffusion in the electrolyte solution and improved charge transfer at the interfaces between photoanodes and electrolytes. The stability of PbS QDs in the electrolyte was also improved by methanol to reduce the charge recombination and prolong the electron lifetime. As a result, the PCE of QDSC was increased to 4.01%.

Role of Ag2S coupling on enhancing the visible-light-induced catalytic property of TiO2 nanorod arrays.

In order to obtain a better photocatalytic performance under visible light, Ag2S-coupled TiO2 nanorod arrays (NRAs) were prepared through the electron beam deposition with glancing angle deposition (GLAD) technique, annealing in air, followed by the successive ionic layer absorption and reaction (SILAR) method. The properties of the photoelectrochemical and photocatalytic degradation of methyl orange (MO) were thus conducted. The presence of Ag2S on TiO2 NRAs was observed to have a significant improvement on the response to visible light. It’s resulted from that Ag2S coupling can improve the short circuit photocurrent density and enhance the photocatalytic activity remarkably.

CdS/ZnS Co-Sensitized Hierarchical TiO2 Nanotree Array with Rutile/Anatase Junctions for Enhanced Photoelectrochemical Performance

Hetero-structured TiO2 nanotree arrays on flurine-doped tin oxide (FTO) substrates were deposited by a two-step hydrothermal method, CdS/ZnS core-shell quantum dots (CdS/ZnS QDs) were deposited by a successive ionic layer absorption and reaction (SILAR) process. The TiO2 nanotree array is composed of a trunk-branch structure where the trunk is rutile TiO2 nanorod array and the branch is anatase TiO2 nanosheets standing on the trunk. Morphology, optical properties and photoelectrochemical (PEC) performances were investigated in detail. After the deposition of CdS/ZnS QDs, TiO2 nanotree array photoanode shows much better PEC performance compared to TiO2 nanorod array photoanode that sensitized nanotree array show a higher photocurrent desity (1.5 mA/cm2) at 1.0 V and almost 2-fold current density (0.29 mA/cm2) than sensitized nanorod array (1.0 mA/cm2 and 0.15 mA/cm2) in the measurement of linear sweep voltammetry (LSV) and transient photocurrent, respectively. This result is due to the enlarged surface specific area for more quantum dots loading, and also due to the rutile/anatase junctions formed on the boundary of trunks and branches, leading to an effective charge separating and transporting. It suggests that the hetero-structured TiO2 nanotree array is very promising to be applied in highly efficient photoanodes for energy devices.

Facile Fabrication of a Silver Nanoparticle Immersed, Surface-Enhanced Raman Scattering Imposed Paper Platform through Successive Ionic Layer Absorption and Reaction for On-Site Bioassays.

We introduce a novel, facile, rapid, low-cost, highly reproducible, and power-free synthesizable fabrication method of paper-based silver nanoparticle (AgNP) immersed surface-enhanced Raman scattering (SERS) platform, known as the successive ionic layer absorption and reaction (SILAR) method. The rough and porous properties of the paper led to direct synthesis of AgNPs on the surface as well as in the paper due to capillary effects, resulting in improved plasmon coupling with interparticles and interlayers. The proposed SERS platform showed an enhancement factor of 1.1 × 10(9), high reproducibility (relative standard deviation of 4.2%), and 10(-12) M rhodamine B highly sensitive detection limit by optimizing the SILAR conditions including the concentration of the reactive solution (20/20 mM/mM AgNO3/NaBH4) and the number of SILAR cycles (six). The applicability of the SERS platform was evaluated using two samples including human cervical fluid for clinical diagnosis of human papillomavirus (HPV) infection, associated with cervical cancer, and a malachite green (MG) solution for fungicide and parasiticide in aquaculture, associated with human carcinogenesis. The AgNP-immersed SERS-functionalized platform using the SILAR technique allowed for high chemical structure sensitivity without additional tagging or chemical modification, making it a good alternative for early clinical diagnosis of HPV infection and detection of MG-activated human carcinogenesis.

Effect of the electrophoretic deposition of Au NPs in the performance CdS QDs sensitized solar Cells

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability alternative for next generation of solar cells, and metallic nanoparticles had shown to be a good alternative to improve specific parameters in such kind of devices. In the present work, it is showed the systematic study of the effect of electrophoretic gold nanospheres (Au NPs) with cadmium sulfide Quantum Dots (CdS QDs) sensitized TiO2 solar cells. Au NPs were added by electrophoretic deposition at several times (0.5, 2.5 and 7.5minutes) and CdS QDs were deposited by a Successive Ionic Layer Absorption and Reaction (SILAR) method. Electrophoretic deposition allowed to significantly decrease the Au NPs deposition times respect previously reported methods. The results show that Au NPs reduce the photocurrent (from 9.85 to 9.44mA/cm2) at the same time that increase the open circuit voltage (Voc) (from 575 to 618mV) and the Fill Factor (FF) (from 46 to 51%) which result in a final increase of the photoconversion efficiency (η) (from 2.63 to 2.96% for 0.5min of deposit). A systematic characterization permitted to identify the origin of the variations observed in the solar cell parameters with and without Au NPs. Incident Photon to Current conversion efficiency (IPCE) demonstrate that the Au NPs reduces the amount of light that reach the CdS QDs and Impedance Spectroscopy (IS) analysis, indicates a downshift in the TiO2 conduction band (CB) and decreases the recombination processes, resulting in the observed increase in the FF and Voc.

Influence of Mn+2 incorporation in CdSe quantum dots for high performance of CdS–CdSe quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) have attracted considerable attention recently and become promising candidates for realizing a cost-effective and facile fabrication of solar cell with improved photovoltaic performance. QDs were directly grown on the TiO2 mesostructure by the successive ionic layer absorption and reaction (SILAR) technique. QDSSC based on CdS–CdSe photoanode achieves a power conversion efficiency of 3.42% under AM 1.5 G one sun illumination. The loading of Mn+2 metal ions was applied to a CdSe (CdS–Mn–CdSe) photoanode to enhance the absorption in QDSSCs, which greatly improved the power conversion efficiency. Without the passivation layer, the solar cell based on a CdS–Mn–CdSe QD-sensitized TiO2 photoelectrode shows higher Jsc (14.67 mA/cm2), Voc (0.590 V) and power conversion efficiency (4.42%) comparing to Mn-undoped CdS–CdSe QD sensitized TiO2 (Jsc: 11.29 mA/cm2, Voc: 0.568 V, and efficiency: 3.42%), which can be ascribed to superior light absorption, faster electron transport and slower charge recombination for the former. The effective electron lifetime of the device with CdS–Mn–CdSe was higher than those with CdS–CdSe, leading to more efficient electron–hole separation and slower electron recombination. The effects of Mn+2 metal ions on the chemical, physical, and photovoltaic properties of the QDSSCs have been investigated have been investigated by X-ray photon spectroscopy (XPS), UV–vis spectra, photocurrent–voltage (J–V) characteristics and electrochemical impedance spectra (EIS).

Improved performance of quantum dots sensitized solar cells using ZnO hierarchical spheres as photoanodes

In this study, the different sizes of ZnO hierarchical spheres (ZnO HS) based on the aggregations of nanoparticles were synthesized through hydrolysis of zinc acetate dihydrate in water and applied to photoanodes of quantum dots-sensitized solar cells (QDSSCs). Among these, ZnO HS with a main diameter of less than 1μm could significantly extend the traveling distance of light within the photoanode films as the scattering centers and ZnO nanoparticles could prevent the decrease of specific surface area. CdS and CdSe quantum dots were deposited by successive ionic layer absorption and reaction (SILAR) method and chemical bath deposition (CBD) respectively. Field-emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM) and X-ray diffraction (XRD) were used to identify the surface profile and crystal structure of ZnO HS photo-electrodes before and after depositing quantum dots. CdS/CdSe co-sensitized ZnO HS photoanodes demonstrated an overall power conversion efficiency of 4.13% under one sun illumination (100mWcm−2), which is higher than that of CdS/CdSe co-sensitized ZnO nanoparticles (ZnO NP) photoanodes.

Fabrication of quantum-sized CdS-coated TiO2 nanotube array with efficient photoelectrochemical performance using modified successive ionic layer absorption and reaction (SILAR) method

Quantum-sized CdS-coated TiO2 nanotube array (Q-CdS-TiO2 NTA) was fabricated by the modified successive ionic layer absorption and reaction method. Scanning electron microscope and transmission electron microscope images showed the regular structure of TiO2 NTA, where quantum-sized CdS (diameter <10nm) deposited on both the inside and outside of TiO2 nanotube wall. Fabrication conditions including immersing cycles, calcination temperature and drying process were well optimized, and the Q-CdS-TiO2 NTA and its photoelectrochemical (PEC) properties were characterized by X-ray fluorescence spectrometer, UV–Vis diffuse reflectance spectra and photovoltage. Distinct increases in visible light absorption and photocurrent were observed as the immersing cycle was increased from 5 to 20 times. The additional drying process accelerated the CdS crystal growth rate, and thus, the fabrication time could be shortened accordingly. Calcination temperature influenced the PEC property of Q-CdS-TiO2 NTA deeply, and the optimized calcination temperature was found as 500 °C. As the Q-CdS-TiO2 NTA was fabricated under such condition, the visible photocurrent density increased to 2.8mA/cm and the photovoltage between 350 and 480nm was enhanced by 2.33 times than that without calcination. This study is expected to optimize Q-CdS-TiO2 NTA fabrication conditions for the purpose of improving its PEC performance.

Controlled engineering of WS2 nanosheets–CdS nanoparticle heterojunction with enhanced photoelectrochemical activity

We report the well-controlled preparation of WS2 nanosheets–CdS nanoparticle heterojunction for photoelectrochemical (PEC) water splitting application. The WS2 nanosheets with an average thickness of ~5nm and lateral dimensions of ~200nm were synthesized via liquid phase exfoliation of bulk WS2 in water/ethanol solution, followed by deposition onto ITO substrate via electrophoretic method. CdS nanoparticles were grown via facile successive ion layer absorption and reaction (SILAR) method. Using these two well-controlled methods, CdS/WS2/ITO and WS2/CdS/ITO systems were fabricated. The loading of WS2 nanosheets was controlled by the deposition condition and the heterojunction was optimized for enhanced photoelectrochemical response under simulated sunlight irradiation. The fabricated electrodes were characterized by various analytical techniques as well as PEC response and electrochemical impedance spectroscopy (EIS). Our results showed that the CdS/WS2/ITO heterojunction exhibits a stable photo-current density which is 3 times higher than the CdS/ITO electrode. In contrast, photo-current density of the WS2/CdS/ITO electrode was lower than that of the bare CdS/ITO, indicating that an appropriate energy level cascade is essential for achieving enhanced PEC response. A charge transfer mechanism was proposed to explain the observed PEC enhancement. This work indicates that the exfoliated WS2 nanosheet is a promising material for stable photoelectrochemical applications.

Effect of the nature of cationic precursors for SILAR deposition on the performance of CdS and PbS/CdS quantum dot-sensitized solar cells

In this work, the influences of cationic precursors on the quality of photoelectrode, consequently on the performance of the quantum dot-sensitized solar cells (QDSCs) have been studied. CdS QDSCs have been prepared using successive ionic layer absorption and reaction (SILAR) method. Three cadmium precursors including nitrate (Cd(NO3)2), chloride (CdCl2), and acetate (Cd(Ac)2) were employed for the synthesis and absorption of CdS nanoparticles on nanostructure TiO2 film. The loading amount and nanoparticle size of the CdS on mesoporous TiO2 film showed a significant difference while using various cadmium precursors in the same SILAR cycles. Both the light-harvesting ability and the obtained incident photon-to-current conversion efficiency values show the trend of deposition rate caused by cadmium precursors. Further, it was proposed that an effective cationic precursor could provide a good connection between QD sensitizer and TiO2 interface by electrochemical impedance spectroscopy analysis. Under AM 1.5 G full one sun illumination, the final power conversion efficiency of CdS QDSC based on Cd(Ac)2 was 2.10 %, and PCE values of 1.57 and 1.20 % were obtained for solar cells sensitized by CdS QDs prepared by CdCl2 and Cd(NO3)2, respectively. The cationic precursor effect was further applied in PbS/CdS co-sensitized solar cells. The PbS/CdS QDSCs based on acetate cationic precursors provide a photocurrent of 19.24 mA/cm2 and PCE of 3.23 % in comparison with 11.26 mA and 2.13 % obtained with nitrate acetate salts. Noticeably, the CdS and PbS/CdS QDSCs based on various cationic precursors prepared by SILAR exhibited good photocurrent stability under several light on–off cycles.

Fabrication of AgInS2 nanoparticles sensitized TiO2 nanotube arrays and their photoelectrochemical properties

TiO2 nanotube arrays sensitized with AgInS2 nanoparticles (TiO2 NTs/AgInS2) were successfully fabricated by a two-step process of anodization followed by a successive ionic layer absorption and reaction (SILAR) method. The structural investigation by scanning electron microscopy and transmission electron microscopy indicated that the AgInS2 nanoparticles of diameters ~15nm grew uniformly on the walls of the TiO2 nanotubes. The TiO2 NTs/AgInS2 exhibits excellent photocurrent and photoelectrocatalytic activities under visible light irradiation. The enhancement in the photoelectrochemical performance could be explained by the optoelectronic coupling between dispersed AgInS2 nanoparticles and TiO2 NTs.

Enhanced tribological performance of CuS thin film on Si substrate: the case of APS-PAA buffer layer

Purpose – The purpose of this paper was to demonstrate the influence of a 3-aminopropyl-triethoxysilane–polyacrylic acid (amino propyl silane (APS)-PAA) buffer layer on the tribological performance of copper sulfide (CuS) thin film on silicon (Si) substrate. Design/methodology/approach – The APS-PAA buffer layer was first deposited on Si substrate by a self-assembling method. Then, the deposited film was coated by a CuS film by a successive ionic layer absorption and reaction (SILAR) method. The structures and morphologies of the prepared films were characterized by X-ray diffraction and atomic force microscopy. The results showed that the prepared CuS film with a PAA-APS double layer had a good crystallinity and surface morphology. The tribological performance of the prepared film was analyzed on UMT-2 tribometer and scanning electric microscope. Findings – With use of an APS-PAA buffer layer, the CuS thin films became compact, smooth and uniform. The tribological performance of the CuS film was greatly enhanced by using an APS-PAA buffer layer. Originality/value – The paper is the first to demonstrate that the CuS film exhibited enhanced structure, morphology and tribological characteristics by using an APS-PAA buffer layer.

Highly-efficient quantum dot-sensitized solar cells based on Sn doped ZnO and CuS electrodes

Highly efficient CdS/CdSe/ZnS quantum dots (QDs) co-sensitized solar cells based on Sn doped ZnO (Sn–ZnO) and CuS electrodes were structured. Sn–ZnO nanoparticle was prepared by hydrothermal method and investigated by X-ray diffraction and N2 adsorption–desorption. The influence of sol-modification and printing process on the crystallinity and morphology of Sn–ZnO photoanode was investigated by scanning electron microscopy (SEM). Semiconductor QDs were grown on sol-modified Sn–ZnO (SM–Sn–ZnO) photoanode by successive ion layer absorption and reaction (SILAR) method and built quantum dot-sensitized solar cells (QDSSCs) based on polysulfide electrolyte. Optimizing the SILAR deposition cycle, the highest conversion efficiency (η) reached 2.07 % by co-sensitization of CdS/CdSe/ZnS, which was 37.09 % higher than SM–ZnO based QDSSCs (η = 1.51 %) under the same condition. CuS electrode was used to replace Pt as the cheap counter electrodes of QDSSCs based on the same photoanodes, which could obviously improve the fill factor of QDSSCs and the conversion efficiency reached 3.37 %.

Research on the Depositon of CdS Quantum Dots on TiO&lt;sub&gt;2&lt;/sub&gt; Inverse Opal

As the third generation solar cells, quantum dot sensitized solar cells (QDSSC) has received wide attention from researchers because of its high theoretical energy conversion efficiency and low production costs. The preparation of CdS quantum dots for TiO2 inverse opal based QDSSC by successive ionic layer absorption and reaction (SILAR) was investigated. The optimized number of SILAR cycle and ionic reaction time was obtained by the analysis of absorption spectra.

Fabrication of CuInSe2 quantum dots sensitized TiO2 nanotube arrays for enhancing visible light photoelectrochemical performance

The CuInSe2 quantum dots (CuInSe2 QDs) sensitization of TiO2 nanotube arrays (TiO2 NTs/CISe) was carried out by a successive ionic layer absorption and reaction (SILAR) method using Cu(Ac)2 and InCl3 as precursors at different Cu/In molar ratio. The deposition of CuInSe2 QDs on the upper and inner surface of the TiO2 NTs was confirmed by field emission scanning electron and transmission electron microscopes. UV-vis absorption and photoelectrochemical measurements indicated that the CuInSe2 QDs sensitization extended the visible light absorption and photocurrent response. The results also showed that TiO2 NTs/CISe largely enhanced the photocatalytic degradation of methyl orange (MO) under visible light irradiation, and showed the excellent activity and stability.

Fabrication of ZnxIn1−xS quantum Dot-sensitized TiO2 nanotube arrays and their photoelectrochemical properties

Complete composition-tuned ZnxIn1−xS (0<x<1) quantum dots were deposited on TiO2 nanotube arrays by the successive ionic layer absorption and reaction (SILAR) method. The deposition of ZnxIn1−xS nanoparticles on the upper and inner surface of the TiO2 NTs was confirmed by field emission scanning electron (FE-SEM) and transmission electron microscopes (TEM). The ZnxIn1−xS/TiO2 nanotube arrays exhibited high absorption in the visible light region due to the narrow band gap of ZnxIn1−xS. Zn0.4In0.6S/TiO2 NTs electrodes showed the optimal photoelectrochemical properties under visible light illumination.