Sequential Ionic Layer Adsorption Reaction Research Articles

Photosensitivity reversal in solution-processed Copper Zinc Tin Sulphide/Cadmium Sulphide superstrate junction

Inverse photosensitivity is a sought-after property for the development of photonic devices and non-volatile memories with low power conversion. Herein, we report on the development of a superstrate-type thin film junction exhibiting inverse photosensitivity which does not involve the use of a pricy transparent conducting oxide layer, providing a method for engineering low-cost thin film devices. Sequential ionic layer adsorption reaction (SILAR) was used to grow Copper Zinc Tin Sulphide (CZTS) and Cadmium sulphide (CdS) large area thin film p-n diode junction. Uniform CZTS thin films with an area of ∼10 cm2 which were free of pin holes or voids could be deposited using an optimized SILAR process recipe. The grown CZTS films exhibited an electrical resistivity of 4.4 × 10−4 Ωm using silver (Ag) electrodes. CdS thin films were sub-sequentially grown over the CZTS layer to form a p-n junction. A knee voltage of 0.2 V in the device configuration “glass/CZTS/CdS/Ag” was observed in the current voltage characteristics. The as-prepared and the vacuum-annealed p-n junction exhibited negative photosensitivity of magnitude 0.21 and 0.16 respectively. The air-annealed device structure exhibited photosensitivity of 216.

Ni foam supported photocathode platform for DNA detection based on antifouling interface

In this work, the photosensitive needle-like Eu: Co3O4 was synthesized on conductive nickel foam (Ni foam) in situ via hydrothermal and subsequent heat treatment, and as the basic material to construct an antifouling photoelectrochemical (PEC) DNA sensor for BRCA1 (breast cancer marker) detection. Ni foam has a great frame structure, which could well control the morphology and size of materials. Then CuS nanoparticles could easily grow on the surface of Eu: Co3O4/Ni foam through a sequential ionic layer adsorption reaction to further enhance the PEC response. For BRCA1 sensitivity analyzing, the excellent antifouling property was realized rely on the conjugation of amino-terminal poly(ethylene glycol) (PEG-NH2). The developed PEC sensor displayed an outstanding stability and great sensitivity under the dissolved oxygen environment, and Ni foam PEC electrode provided potential application for other photosensitive materials-controlled preparation.

Deposition of CZTS|ZnO Hetero-Junction Using SILAR and Spray Pyrolysis

Copper zinc tin sulphide (CZTS) thin films have been deposited on glass substrate at 323 ± 5 K using sequential ionic layer adsorption reaction (SILAR). The number of SILAR cycles required for optimum crystalline quality CZTS thin films was optimized. The as-deposited CZTS thin films showed kesterite crystalline structure with preferential orientation along (103) plane. Structural, optical, electrical, and morphological properties of the films changed when the as-prepared films were subjected to annealing in a vacuum chamber maintained at 3 × 10–4 Torr at temperatures of 473, 573, and 673 K. Film resistivity was found to decrease exponentially as the annealing temperature was increased. We have achieved a resistivity of 4.4 × 10–4 Ω m for the as-prepared thin film, which is lowest among SILAR-grown films at temperature lower than 373 K without any post-deposition processing. A superstrate-type p–n junction was fabricated by growing nano-structured zinc oxide (ZnO) on top of the glass|CZTS structure using chemical spray pyrolysis technique. The photosensitivity of the p–n junction was reversed when the structure was subjected to vacuum annealing at 673 K.

Band gap engineered ternary semiconductor PbxCd1−xS: Nanoparticle‐sensitized solar cells with an efficiency of 8.5% under 1% sun—A combined theoretical and experimental study

AbstractWe report the synthesis and photovoltaic properties of a ternary metal sulfide alloyed semiconductor PbxCd1−xS prepared by the two‐stage sequential ionic layer adsorption reaction. The synthesized PbxCd1−xS nanoparticles (NPs) retain the hexagonal structure of the CdS host with Pb substituting a fraction of the Cd atom (x = 0‐0.17). Band structures of PbxCd1−xS with various Pb contents x were calculated using the complementary density functional theory (DFT) method. Optical, quantum efficiency, cyclic voltammetry measurements, and band structure calculation revealed that the band gap of PbxCd1−xS decreased with increasing x, resulting in an increased optical absorption band from 500 to 720 nm (1.73‐2.44 eV) for x = 0 to 0.17. Solid‐state PbxCd1−xS semiconductor nanoparticle‐sensitized solar cells (NSSCs) were fabricated from the synthesized NPs using spiro‐OMeTAD as the hole‐transporting material. The best Pb0.05Cd0.95S cell yielded a power conversion efficiency (PCE) of 3.67%, a Voc of 0.70 V, and a fill factor (FF) of 62.8% under 1 sun. The PCE increased to 5.93% under a reduced light intensity of 0.1 sun and further increased to 8.48% under 0.01 sun. The external quantum efficiency (EQE) spectrum covers the spectral range of 300 to 730 nm with a maximal EQE of 82% at λ = 580 nm. The PCE over 8% can be categorized into a high‐efficiency NSSCs. In addition, the Voc of 0.70 V is a relatively high Voc among all NSSCs. The high PCE and Voc suggest that PbxCd1−xS has potential to be an efficient solar absorber.

Sequential ionic layer adsorption reaction formation of LaVO4–TiO2 nanocomposites for photocatalytic water treatment

Lanthanum vanadate (LaVO4) has been deposited onto the surface of P25 TiO2 particles immobilized on glass beads for photocatalytic water treatment.

Bandgap Tunable Ternary Cd x Sb2-y S3-δ Nanocrystals for Solar Cell Applications.

We report the synthesis and photovoltaic performance of a new nonstoichiometric ternary metal sulfide alloyed semiconductor–CdxSb2–yS3−δ nanocrystals prepared by the two-stage sequential ionic layer adsorption reaction technique. The synthesized CdxSb2–yS3−δ nanocrystals retain the orthorhombic structure of the host Sb2S3 with Cd substituting a fraction (x = 0–0.15) of the cationic element Sb. The CdxSb2–yS3−δ lattice expands relative to the host, Sb2S3, with its lattice constant a increasing linearly with Cd content x. Optical and external quantum efficiency (EQE) spectra revealed that the bandgap Eg of CdxSb2–yS3−δ decreased from 1.99 to 1.69 eV (i.e., 625–737 nm) as x increased from 0 to 0.15. Liquid-junction CdxSb2–yS3−δ quantum dot-sensitized solar cells were fabricated using the polyiodide electrolyte. The best cell yielded a power conversion efficiency (PCE) of 3.72% with the photovoltaic parameters of Jsc = 15.97 mA/cm2, Voc = 0.50 V, and FF = 46.6% under 1 sun. The PCE further increased to 4.86%, a respectable value for a new solar material, under a reduced light intensity of 10% sun. The PCE (4.86%) and Jsc (15.97 mA/cm2) are significantly larger than that (PCE = 1.8%, Jsc = 8.55 mA/cm2) of the Sb2S3 host. Electrochemical impedance spectroscopy showed that the ZnSe passivation coating increased the electron lifetime by three times. The EQE spectrum of CdxSb2–yS3−δ has a maximal EQE of 82% at λ = 350 nm and covers the spectral range of 300–750 nm, which is significantly broader than that (300–625 nm) of the Sb2S3 host. The EQE-integrated current density yields a Jph of 11.76 mA/cm2. The tunable bandgap and a respectable PCE near 5% suggest that CdxSb2–yS3−δ could be a potential candidate for a solar material.

A novel photoelectrochemical singal amplification assay for procalcitonin detection based on ZnxBi2S3+x sensitized NiTiO3 matrix

An original signal amplification photoelectrochemical (PEC) immunosensor for procalcitonin detection was fabricated based on ZnxBi2S3+x sensitized NiTiO3 nanorods. Using ethylene glycol as medium, the NiTiO3 nanorods were successfully manufactured after calcination in air atmosphere, the rod-like structure have rough surface that produced benefit to capture lots of functional ZnxBi2S3+x, the sensitizer sensitized NiTiO3 on ITO substrate by means of a sequential ionic layer adsorption reaction, and the obtained ZnxBi2S3+x/NiTiO3 composites showed an excellent absorption of visible light owing to the matched band gap. By the way, ZnxBi2S3+x/NiTiO3 composites as mimic enzyme of glucose oxidase, high sensitivity was achieved due to the generated H2O2 as holes scavenger when glucose added, that promote the photo electrons transfer quickly, further increased the PEC signal. The as prepared sensor showed a large linear range of 0.0001–50 ng·mL−1 with 0.04 pg·mL−1 detection limit. Simultaneously, the signal amplification strategy of this sensor provides applicable to other PEC immunosensors for detection of other targets.

Photocatalytic Behavior of SILAR-Grown Nano-flaked CdS

An undemanding and cost-effective low-temperature sequential ionic layer adsorption reaction process has been used to synthesize cadmium sulfide (CdS) thin films on glass substrates. The as-deposited films were photoconductive in nature with a photosensitivity of ~ 10, and their sensitivity could be improved using a post-deposition annealing process sequence to ~ 650. We have grown nano-flaked CdS and tested their efficacy for the photo-catalytic degradation of Rhodamine B dye molecules. We report that the nano-flaked CdS has an inherent Rhodamine B dye decay pathway which is active even in the absence of visible radiation. We also report on the Rhodamine B dye decay by the nano-flaked CdS under direct sunlight illumination. Our results prove that the kinetics of the photocatalysis is directly related to the photoconductive nature of the films. The highly photosensitive nature of the nano-flaked CdS films leads to alternate dye degradation pathways which enhance the kinetics of the reaction.

Tunable Optical Properties in SnxSb2–yS3: A New Solar Absorber Material with an Efficiency of near 5%

This work investigates the synthesis of a new ternary alloyed metal sulfide semiconductor SnxSb2–yS3 and its application in solar cells. SnxSb2–yS3 nanocrystals were synthesized by incorporating Sn2+ ions into the host binary Sb2S3 semiconductor using a two-step sequential ionic layer adsorption reaction (SILAR) process. The ternary SnxSb2–yS3 semiconductor maintains the monoclinic crystalline structure of the binary Sb2S3 host with a small expansion in lattice constants relative to that of Sb2S3. Energy-dispersive X-ray analysis revealed the nominal chemical composition of the sample with eight SILAR cycles to be Sn0.52Sb1.48S3. The energy gap Eg of SnxSb2–yS3 decreases with increasing Sn content x, resulting in a tunable Eg from 620 to 800 nm (i.e., 2.0–1.5 eV) for x = 0–0.56. Liquid-junction quantum dot-sensitized solar cells were fabricated, for the first time, from the prepared SnxSb2–yS3 nanocrystals using the polyiodide electrolyte. The best cell yielded an efficiency of 2.58% with the photovoltaic parameters of Jsc = 14.04 mA/cm2, Voc = 0.46 V, and FF = 39.9% under 1 sun. The efficiency improved to a respectable value of 4.89% under the reduced light intensity of 0.05%. The external quantum efficiency (EQE) spectrum has a maximal EQE of 71.8% at λ = 500 nm and covers the spectral range of 300–800 nm, which is significantly broader than that (300–620 nm) of the host Sb2S3. The broader optical absorption band increases light harvesting and results in a Jsc ≈ 64% larger than that of the host Sb2S3. The result demonstrates the tunable optical properties of SnxSb2–yS3 by controlling the cationic Sn and Sb compositions, which is a favorable property for a solar absorber.

Ultrathin Ti/TiO2/BiVO4 nanosheet heterojunction arrays for photoelectrochemical water oxidation

Bismuth vanadate (BiVO4) photoanode has attracted intensive attention recently due to its narrow band gap and suitable band edges. However, BiVO4 is suffered from slow charge transportation and short carrier diffusion length resulting a low energy conversion efficiency. Herein, we proposed a strategy for fabricating ultrathin Ti/TiO2/BiVO4 nanosheet heterojunction arrays by a sequential ionic layer adsorption reaction (SILAR) method depositing BiVO4 on top of Ti/TiO2 nanosheet arrays. The photocurrent of Ti/TiO2/BiVO4 photoanode prepared at the precursor concentration of 0.04 M is 1.2 μA/cm2 and increase to 5.8 μA/cm2 for that of 0.02 M. The ultrathin Ti/TiO2 nanosheet arrays possess an ideal surface area for coupling nanoscale BiVO4 as much as possible to construct heterojunction interfaces, which not only shorten the charge transfer pathway but also provide a flexible and strong conductive charge collector. Besides, the formation of heterojunctions between ultrathin TiO2 and BiVO4 favors the photoinduced electrons transfer from BiVO4 to TiO2 suppressing the recombination of photogenerated electron-hole pairs effectively.

Eco-Friendly NaSbS2 Quantum Dot-Sensitized Solar Cells

Ternary sulfide NaSbS2 is a low-cost, environmentfriendly semiconductor that has rarely been studied. This paper demonstrates, for the first time, solid-state NaSbS2 quantum dot-sensitized solar cells (QDSSCs). NaSbS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles were synthesized using the sequential ionic layer adsorption reaction method. Solid-state QDSSCs were fabricated from the synthesized nanoparticles using spiro-OMeTAD as the hole-transporting electrolyte. The best cell yielded an efficiency of 1.27% under 1 sun. At the reduced light intensity I0 of 10% sun, the efficiency increased significantly to 4.11% with an open-circuit voltage Voc of 0.51 V, a short-circuit current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> of 1.68 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and a fill factor (FF) of 47.8%. A sublinear power law of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ∝ I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sup> accounts for the large improvement in performance under low-light intensities because of the reduced carrier recombination. The external quantum efficiency (EQE) spectrum covered the spectral region of 300-750 nm with a maximum EQE value of 72% at λ = 450 nm. The present efficiency (4.11%) represents about 30% improvement over the best previous result (3.18%) of liquid-junction QDSSCs. The respectable efficiency indicates that NaSbS2 shows potential as an efficient solar absorber material.

Gas selectivity of SILAR grown CdS nano-bulk junction

Nano-particles of cadmium sulphide were deposited on cleaned copper substrate by an automated sequential ionic layer adsorption reaction (SILAR) system. The grown nano-bulk junction exhibits Schottky diode behavior. The response of the nano-bulk junction was investigated under oxygen and hydrogen atmospheric conditions. The gas response ratio was found to be 198% for Oxygen and 34% for Hydrogen at room temperature. An increase in the operating temperature of the nano-bulk junction resulted in a decrease in their gas response ratio. A logarithmic dependence on the oxygen partial pressure to the junction response was observed, indicating a Temkin isothermal behavior. Work function measurements using a Kelvin probe demonstrate that the exposure to an oxygen atmosphere fails to effectively separate the charges due to the built-in electric field at the interface. Based on the benefits like simple structure, ease of fabrication and response ratio the studied device is a promising candidate for gas detection applications.

BiVO4 -TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method.

Composite photocatalyst films have been fabricated by depositing BiVO4 upon TiO2 via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP-OES), XPS, photoluminescence and Mott-Schottky analyses. SILAR processing was found to deposit monoclinic-scheelite BiVO4 nanoparticles onto the surface, giving successive improvements in the films' visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO4 conduction band and valence band lying cathodically shifted from those of TiO2 . The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo-first-order rate constant of 0.004 min(-1) . As a reference material, the same SILAR modification has been made to an inactive wide-band-gap ZrO2 film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO4 -ZrO2 system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self-sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst's conduction band.

Effect of vacuum annealing on the photoconductivity of CuO thin films grown using sequential ionic layer adsorption reaction

Using sequential ionic layer adsorption reaction technique, Cupric Oxide (CuO) thin films were deposited on a glass substrate at relatively low bath temperature of 338 ± 5 K. The as deposited films were polycrystalline in nature with preferential orientation along the (200) plane. The films were found to exhibit negative photoconductivity. Vacuum annealing of the films resulted in preferential growth along the (111) and (200) plane for temperatures 373 K, 473 K and 573 K. Vacuum annealing at 673 K resulted in preferential growth along the (200) plane. The vacuum annealed films showed normal photoconductivity behavior. The optical band gap of the films was found to increase from 1.57 eV for the as prepared films to 2.06 eV for films annealed in vacuum at 673 K. Surface photo voltage measurements indicate that the direction of band bending is reversed when the as deposited CuO thin films are subjected to vacuum annealing. We conclude that surface state passivation is leading to change in the photoconductive behavior of the thin film samples when subjected to post deposition vacuum annealing.

(Invited) Progress on Electroless Atomic Layer Deposition

Atomic layer deposition (ALD) is a group of methods for the formation of nanofilms of materials, an atomic layer at a time using surface limited reactions. The majority of those methods are based on use of the vacuum environment. However there are methods such as sequential ionic layer adsorption reaction (SILAR) which uses the condensed phase, that is, aqueous solutions of precursor ions. In addition, this group has been working on an electrochemical form of ALD for 25 years. That work is referred to as electrochemical atomic layer deposition (E-ALD) or electrochemical atomic layer epitaxy (EC-ALE), and is based on using underpotential deposition (UPD) for surface limited reactions. The problem with using an electrochemical methodology for the formation of nanofilms is that many compatible with the conductive substrates normally used for E-ALD. This has stimulated investigations into the growth of materials using an electroless form of ALD (EL-ALD). The processes being explored are based on use of an adsorbed layer of a precursor, where the solution is then exchanged for a reducing agent, or vis versa. This cycle is then repeated to desired thickness. One example is the use of an adsorbed (or absorbed) layer of hydrogen as the reducing agent (usually on Pd). This is then used for surface limited redox replacement (SLRR) of the desired element. Another example is the use of Sn2+ adsorption followed by Pd2+, which oxidizes the Sn2+ to Sn4+ and forms Pd on the surface. Studies are underway to build this into a cycle for EL-ALD.

In situ synthesis of Bi2S3 sensitized WO3 nanoplate arrays with less interfacial defects and enhanced photoelectrochemical performance.

In this study, Bi2S3 sensitive layer has been grown on the surface of WO3 nanoplate arrays via an in situ approach. The characterization of samples were carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and ultraviolet–visible absorption spectroscopy (UV-vis). The results show that the Bi2S3 layer is uniformly formed on the surface of WO3 nanoplates and less interfacial defects were observed in the interface between the Bi2S3 and WO3. More importantly, the Bi2S3/WO3 films as photoanodes for photoelectrochemical (PEC) cells display the enhanced PEC performance compared with the Bi2S3/WO3 films prepared by a sequential ionic layer adsorption reaction (SILAR) method. In order to understand the reason for the enhanced PEC properties, the electron transport properties of the photoelectrodes were studied by using the transient photocurrent spectroscopy and intensity modulated photocurrent spectroscopy (IMPS). The Bi2S3/WO3 films prepared via an in situ approach have a greater transient time constant and higher electron transit rate. This is most likely due to less interfacial defects for the Bi2S3/WO3 films prepared via an in situ approach, resulting in a lower resistance and faster carrier transport in the interface between WO3 and Bi2S3.

Negative resistance in Cu2O/In2S3 heterostructure

A semiconductor hetero-structure exhibiting photovoltaic effect was grown by a combination of sequential ionic layer adsorption reaction and chemical spray pyrolysis technique. The forward current–voltage characteristic of the device showed a dynamic negative resistance region. It was observed that the onset of the dynamic negative resistance can be tuned by the illumination intensity of the incident light. Low temperature electrical studies of the device showed the presence of shallow states at ∼80 meV and ∼15 meV in the band structure. Work function measurement using Kelvin Probe proved the presence of inverted bands in this hetero structure. Shallow states trapped within these bands may be responsible for the negative resistance exhibited by the hetero-structure.

Highly Efficient Photoelectrochemical Hydrogen Generation Using Zn(x)Bi2S(3+x) Sensitized Platelike WO₃ Photoelectrodes.

Zn(x)Bi2S(3+x) sensitized platelike WO3 photoelectrodes on FTO substrates were for the first time prepared via a sequential ionic layer adsorption reaction (SILAR) process. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet visible spectrometry (UV-vis), and Raman spectra. The results show that the ZnxBi2S3+x quantum dots (QDs) are uniformly coated on the entire surface of WO3 plates, forming a WO3/Zn(x)Bi2S(3+x) core/shell structure. The Zn(x)Bi2S(3+x)/WO3 films show a superior ability to capture visible light. High-efficiency photoelectrochemical (PEC) hydrogen generation is demonstrated using the prepared electrodes as photoanodes in a typical three-electrode electrochemical cell. Compared to the Bi2S3/WO3 photoelectrodes, the Zn(x)Bi2S(3+x)/WO3 photoelectrodes exhibit good photostability and excellent PEC activity, and the photocurrent density is up to 7.0 mA cm(-2) at -0.1 V versus Ag/AgCl under visible light illumination. Investigation of the electron transport properties of the photoelectrodes shows that the introduction of ZnS enhances the photoelectrons' transport rate in the photoelectrode. The high PEC activity demonstrates the potential of the Zn(x)Bi2S(3+x)/WO3 film as an efficient photoelectrode for hydrogen generation.

Electroless Atomic Layer Deposition

Atomic layer deposition (ALD) is a group of methods for the formation of nanofilms of materials, an atomic layer at a time using surface limited reactions. The majority of those methods are based on use of the vacuum environment. However there are methods such as sequential ionic layer adsorption reaction (SILAR) which used the condensed phase, that is, aqueous solutions of precursor ions. In addition, this group has been working on an electrochemical form of ALD for 25 years. That work is referred to as electrochemical atomic layer deposition (E-ALD) or electrochemical atomic layer epitaxy (EC-ALE), and is based on using underpotential deposition (UPD) for surface limited reactions. The problem with using an electrochemical methodology for the formation of nanofilms is that many substrates are not conductive. This has stimulated investigations into the growth of materials using an electroless form of ALD (EL-ALD). An example of an EL-ALD process would be the use of a solution containing H2 to poise the potential of a Pd surface. This will result in the adsorption of a layer of hydrogen atoms which can then be exposed to precursors for Pt or Pd, forming an atomic layer of the metal. That process can then be repeated to grow a nanofilm. That example takes place on a conducting surface, however. Work is continuing on development of an EL-ALD method which can start on an insulating surface, and results will be discussed.