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The Raman analysis of Cu2ZnSn(S,Se)4 thin films revealed a change in the relative defect concentration and device performance with composition.

Point defect engineering in Cu2ZnSnSe4 (CZTSe) thin films is the main issue to improve its device performance. This study reveals the correlation between the reaction pathway and the point defects in the CZTSe film. The reaction pathway from a metallic precursor (Mo/Zn/Sn/Cu) to a kesterite CZTSe film is varied by changing the annealing process. The synthesized CZTSe films under different reaction pathways induce different device performances with different defect energy levels, although all CZTSe films have similar structural and optical properties (Eg ∼ 1.0 eV). The admittance spectroscopy demonstrates the correlations between point defect types (VZn, ZnSn, ZnCu, CuZn, and VCu) and the reaction pathways for the formation of CZTSe films. The different growth rates of binary selenides, such as ZnSe and/or Sn-Se phases, during the annealing process are especially strongly related to the formation of point defects, leading to the different open-circuit voltages (396-451 mV) and fill factors (51-65%). The results of this study suggest that controlling the reaction pathway is an effective approach to adjust the formation of defects in the kesterite CZTSe film as well as to fabricate high-performance solar cell devices.

A cation substitution in Cu2ZnSn(S,Se)4 (CZTSSe) offers a viable strategy to reduce the open-circuit voltage (Voc)-deficit by altering the characteristics of band-tail states, antisite defects, and...

Kesterite surface properties and band alignment behavior at an absorber/buffer interface are key issues for highly efficient kesterite solar cell devices. Herein, we report new insights into surface and interface engineering and favorable band alignment of Cu2ZnSnSe4 (CZTSe)/CdS buffer in solar cells via in situ formed ZnSe nanoparticles (NPs) on the CZTSe surface. The device characteristics and junction qualities of the CZTSe solar cells with in situ formed ZnSe NPs are improved even though they have similar bulk properties to CZTSe thin films. X-ray photoelectron spectroscopy (XPS) characterization revealed a favorable conduction band offset (CBO, +0.26 eV) for CZTSe/ZnSe NPs/CdS compared to that for CZTSe/CdS (+0.01 eV) and CZTSe/ZnSe layer/CdS (+0.976 eV), respectively. In this regard, we also postulated a formation mechanism for in situ formed ZnSe NPs on the CZTSe surface via annealing of metallic precursors with different stacking orders. This work offers a simple and source-free interface engineering strategy using in situ formed ZnSe NPs (secondary phase) on the CZTSe surface to further improve the performance of kesterite solar cell devices.

Transition-metal phosphide (TMP) nanostructures have been extensively studied for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, phase-controlled synthesis of collo...

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 10/03/2021 Here, a three-dimensional (3D) core–shell nanohybrid based on few-layer amorphous Co–Fe–Bi nanosheets directly grown on crystalline NiCo2O4 nanowires supported on the Ni foam (Co–Fe–Bi/NiCo2O4/NF) are facilely fabricated as highly efficient and durable electrocatalysts for water oxidation. This self-standing 3D core–shell nanohybrid design with unique materials chemistry and excellent interface engineering enhances the mass transport and stimulates the production of active sites during the oxygen evolution reaction. Serving as the anode catalysts, the resulting self-standing Co–Fe–Bi/NiCo2O4/NF nanohybrid electrocatalysts show a better electrocatalytic activity with an overpotential of 227 mV at 10 mA/cm2, a Tafel slope of 45 mV dec–1, excellent durability over 40 h, and the ability to deliver a current density of 200 mA/cm2 at an overpotential of ∼410 mV in an alkaline medium. Thus, the excellent electrocatalytic performance of the Co–Fe–Bi/NiCo2O4/NF nanohybrid demonstrates the importance of design and development of core–shell nanohybrids for large-scale practical applications in a multitude of energy conversion devices.

A vertical half-wavelength RF cavity was designed for SKKUCY-10 cyclotron . The design of the RF cavity was implemented in three stages as follows. Firstly, the structure of the cavity was modeled as an HWR without Dee geometry. Secondly, the Dee configuration including geometry was modeled, and finally, the power coupler, fine tuner, and the central region including ion source and puller were designed. For the first structure, the length of the resonator was selected as 560 mm to minimize the resonance frequency. For the second structure, the resonance frequency, unloaded quality factor ( Q 0 ) and electric field strength were simulated to be 83.2 MHz, 5830 and 7.8 MV/m, respectively. A coupling coefficient of ( β ) 0.98 and characteristic impedance ( Z 0 ) of 50 Ω were obtained for the final structure. The RF cavity was fabricated based on design and resonance frequency, coupling coefficient were measured 83.2 MHz, 1.09, respectively. The reflection ratio of 5 ± 0.1% and cavity pick-up power of 0–0.12 μ W were tested by increasing the input RF power from 0 to 9 mW. The specifications of the RF cavity showed that there is a good agreement between the simulation and experimental results.

We demonstrate that graphene can enhance the etch resistance of polymeric hardmask significantly. Graphene oxide with a sub-micrometer diameter (nGO) was functionalized with fluorinated poly(hydroxyamide) (FPHA) via a chemical coupling reaction. The FPHA-functionalized-nGO can be dispersed in various organic solvents including methanol, cyclohexanone, dimethylformamide, and N-methyl pyrrolidone. In addition, the dispersions were spincoated to prepare hardmask films which were then thermally annealed to produce nRGO-fluorinated-polybenzoxazole (FPBO) film. Compared to pristine FPBO film, elastic modulus (122%), hardness (92%), and etch resistance (54%) were significantly enhanced at 17 wt.% graphene loading, surpassing the properties of commercial CHM009 film.

Here, a hierarchical nanostructure composed of Ni-doped α-FeOOH (Ni:FeOOH) nanosheets coupled with N-doped graphite foam (NGF) is demonstrated as a three-dimensional (3D) self-supported electrocata...

A cation substitution in Cu

We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 °C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 °C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.

A self‐cleaning bar screen is often used in the first filtration level of a wastewater treatment plant to screen out solid debris from sewage water. The screening process of the bar screen was numerically investigated using the arbitrary Lagrangian–Eulerian method to model the fluid–structure interaction between the sewage water and bar screen. The bar screen design is improved by installing a rotating subscreen under the bar screen to prevent solid waste from passing through. The effects of bar screen on the water flow were examined using hydrodynamic properties. The structural properties were estimated to observe the effects of water flow on the parts of the bar screen. Various inlet flow rates and positions of subscreen and rake were used to examine their effects on velocity, pressure coefficient, structural deformation and von Mises stress. The screening process decreased with the increase in sewage flow rates. The water flow significantly affected the bar screen when the subscreen and rake are not in contact.

Herein, we report a facile process, i.e., controlling the initial chamber pressure during the postdeposition annealing, to effectively lower the band tail states in the synthesized CZTSSe thin films. Through detailed analysis of the external quantum efficiency derivative (dEQE/dλ) and low-temperature photoluminescence (LTPL) data, we find that the band tail states are significantly influenced by the initial annealing pressure. After carefully optimizing the deposition processes and device design, we are able to synthesize kesterite CZTSSe thin films with energy differences between inflection of d(EQE)/dλ and LTPL as small as 10 meV. These kesterite CZTSSe thin films enable the fabrication of solar cells with a champion efficiency of 11.8% with a low Voc deficit of 582 mV. The results suggest that controlling the annealing process is an effective approach to reduce the band tail in kesterite CZTSSe thin films.

In successive alkalinity-producing systems (SAPS), the limestone tends to get coated with precipitates, reducing the permeability of the SAPS, the mine water treatment efficiency, and the service life of the SAPS. Further study of the precipitates are required to improve the design of flushing systems. In this study, the growth characteristics, particle size distribution, and chemical composition of these precipitates were determined. Based on their growth characteristics, precipitates were classified into four types, and the critical velocity of the precipitates, which is a design parameter of flushing systems, was evaluated through experiments. The resulting critical velocity was used to identify the minimum number of orifices required for lateral pipes in flushing systems.

A compact 6 MeV electron linear accelerator (linac), intended to be used as an X-ray source for a dual-head gantry radiotherapy system has been developed. In order to meet the size requirements of the dual-head gantry machine, an X-band radio frequency (RF) technology is used, which facilitates a reduction in the size of the linac, which is nine times smaller than the conventional medical purpose linac using S-band RF technology. Nevertheless, the X-band RF technology requires much higher machining precision and higher-quality surface finish owing to the electrical breakdown phenomena resulting from its small size. After the design was completed, the RF cavity was machined using high-precision machining technology, achieving machining tolerances of ±2 μm, and a surface roughness less than 50 nm. Various RF properties were measured in the fabricated RF cavity by using a network analyzer, and the distribution of the electric field generated in the RF cavity was verified by a bead-pull measurement technique. RF conditioning and beam commissioning experiments were performed, following the fabrication and tuning of the RF cavity.

Alzheimer's disease (AD) is characterized by amyloid beta (Aβ) plaques and neurofibrillary tangles. AD drug development has been limited due to the presence of the blood–brain barrier (BBB), which prevents efficient uptake of therapeutics into the brain. To solve this problem, we used trans-activator of transcription (TAT)-transducing domain and added the human serum albumin (HSA) carrier to increase the half-life of the drug within the body. In addition, we included the protein of interest for lowering Aβ deposition and/or neurofibrillary tangles. We made HSA fusion protein (designated AL04) which contains Cystatin C (CysC) as core mechanism of action moiety in the construct containing tandem repeat TAT (dTAT). After purification of 80KDa AL04, we investigate the therapeutic potential of AL04 in vitro and AD mouse model Tg2576. We evaluated the permeability of AL04 through the BBB using a cell-based human BBB model and show that dTAT plays a role in facilitating the delivery of 80 kDa protein. We found out that AL04 attenuates Aβ-induced neurotoxicity in PC12 cells. In Tg2576 mice brain, Aβ plaques were dramatically reduced in AL04 treated mice. These data suggest that BBB-crossing albumin fusion protein AL04 with CysC active moiety can be a disease modifying treatment for AD.

Quintenary Cu2(Zn1−xCox)SnS4 is an analog of the promising solar absorber material Cu2ZnSnS4 (CZTS). The initial rapid progress in CZTS has stalled because the similar sizes of Cu and Zn cations lead to facile formation of antisite defects, which are thought to limit the solar cell performance. Cobalt substitution for Zn may reduce cation disorder. Herein, we report the synthesis of wurtzite Cu2(Zn1−xCox)SnS4 across the entire composition range and a systematic study of the substitution of Co into the wurtzite CZTS lattice. The synthesis is based on microwave heating to only 160 °C and uses metal salts and thiourea as precursors and ethylene glycol as the solvent. The Cu2(Zn1−xCox)SnS4 nanocrystals were phase pure wurtzite within the detection limits of X-ray diffraction and Raman scattering. The wurtzite lattice parameters, nanocrystal sizes, and A1 Raman mode peak positions depend on the Co concentration, x. The lattice parameters follow Vegard's law within the accuracy of our measurements, and the A1 Raman mode shifts nearly linearly with x. The nanocrystal size decreases from 8 nm to 4 nm as x increases from 0 to 1. The absorption band edge blue shifted from 1.1 eV for x = 0 to 1.35 eV for x = 1. These values are lower than those predicted by density functional theory calculations and previous attempts at determining the optical band gap for wurtzite Cu2ZnSnS4 (x = 0) and Cu2CoSnS4 (x = 1). Either the band gaps of wurtzite Cu2ZnSnS4 (x = 0) and Cu2CoSnS4 (x = 1) are lower or these materials have significant band tails due to defects. We also prepared polycrystalline Cu2(Zn1−xCox)SnS4 thin films by thermal annealing, in sulfur, of coatings comprised of Cu2(Zn1−xCox)SnS4 nanocrystals. Upon annealing in sulfur, the wurtzite Cu2(Zn1−xCox)SnS4 nanocrystals transformed into larger grains (100 s of nm to microns) that have a kesterite structure. The films with x ≤ 0.4 were phase pure kesterite within the detection limits of XRD and Raman scattering, but, for x ≥ 0.6, secondary phases such as Cu1.96S and Co0.24Zn0.76S were also detected.

A low-cost, highly efficient and durable photoelectrochemical (PEC) water-splitting system can be realized through designing a hierarchical core/shell nanostructured photoanode entirely composed of Earth-abundant elements. Herein, we report the rational design of a core/shell nanostructured photoanode with a TiO2 nanorod (NR) array as the core and a highly active Earth-abundant NiFe oxyhydroxide ((Ni1−xFex)OOH, NiFeOOH) oxygen evolution catalyst (OEC) as the shell for PEC water oxidation. Specifically, the NiFeOOH nanosheets were prepared via a facile, one-step electroless deposition method for a short reaction time of 10 min at room temperature. The TiO2/NiFeOOH core/shell nanostructured photoanode exhibits an unprecedented enhancement in photocurrent density (3.85 mA cm−2 at 1.23 V vs. a reversible hydrogen electrode, (RHE)), no decay in photocurrent density over 24 h, and an obvious cathodic onset potential shift of 133 mV compared to the TiO2 NRs (0.73 mA cm−2 at 1.23 V vs. RHE). The electron transfer mechanism is discussed through electrochemical impedance spectroscopy studies and calculated band alignments via ultraviolet photoelectron spectroscopy characterization. This work not only suggests a simple, room temperature electroless strategy for integrating Earth-abundant catalysts with photoanodes, but also accelerates the development of rationally designed core/shell photoanodes for efficient and durable solar water oxidation.

Recently, emerging Cu–Sb–S-based compounds have been identified as an attractive candidate for photovoltaic (PV) applications because of their high natural abundance, eco-friendly features and typical phase-dependent characteristics. Herein, a simple eutectic solvent-mediated (choline chloride/ethylene glycol) synthetic approach for newly debuted Cu–Sb–S-based nanocrystals (NCs) with phase-selective properties is presented. This combination of material and preparation method may promote the exchange of carriers by avoiding a steric hindrance for a facile charge transport encountered in NCs prepared using amines, thiols, hydrazines and phosphine oxide solvents. A temperature-dependent study of an ethaline-based deep eutectic solvent (DES) is conducted to elucidate the characteristics of associated chemical shifts and vibrations and to determine changes in hydrogen bonding interactions using structural and thermal analytical techniques. The results suggest that ethaline is a strong candidate as a greener solvent for the synthesis of NCs at relatively low temperatures. The electronic structures of all four Cu–Sb–S phases—Cu3SbS4, CuSbS2, Cu3SbS3, and Cu12Sb4S13—were simulated using the Vienna ab initio Simulation (VASP) code, projector augmented-wave (PAW) potentials and the hybrid functional method (HSE 06) and using density functional theory for combined theoretical and experimental studies. Discrepancies between the experimental and theoretical bandgap values of 0.29, 0.18, 0.12 and 0.16 eV were observed for Cu3SbS4, CuSbS2, Cu3SbS3 and Cu12Sb4S13 compounds, respectively. A photoelectrochemical (PEC) water reduction system with a Mo/photoelectrode/CdS/Pt/electrolyte configuration generated a cathodic photocurrent of −1.28 and −2.72 mA cm−2 for Cu3SbS4 and CuSbS2 electrodes, respectively, at 0 V versus the reversible hydrogen electrode (VRHE) under AM 1.5 G illumination, demonstrating the great potential of NCs prepared via eutectic solvent-mediated synthesis. This is the first successful attempt to apply eutectic solvent-mediated Cu–Sb–S NCs for solar driven H2 production. These outcomes suggest that designing proper functional materials through the application of greener synthesis strategies can improve water-splitting performance and would help meet the perpetual technological need for greener methods.

Deep eutectic solvents (DESs) based on choline chloride/ethylene glycol have been explored as synthetic media for recently introduced Cu–Sb–S based colloidal quantum dots (CQDs) decorated on NiO/fluorine-doped tin oxide (FTO) and TiO2/FTO photoelectrodes for unassisted solar water splitting for hydrogen generation. The feasibility of the use of an environmentally benign solvent-based synthetic process is demonstrated herein by preparing the earth-abundant Cu–Sb–S-based CQDs and utilizing them in a solar energy harvesting material for photoelectrochemical (PEC) water splitting while avoiding the use of sacrificial agents. The band alignment between CQDs and NiO or TiO2 clearly suggests that the CQD-modified NiO and TiO2 electrodes act as a potential photocathode (NiO/Cu3SbS4/ZnS) and photoanode (TiO2/CuSbS2/ZnS) with faradaic efficiencies of up to 74 and 86%, respectively, which allows us to construct an efficient PEC cell to split water at an overall solar-to-hydrogen (STH) efficiency of ∼0.28%. The tandem photoelectrode configuration in an unassisted mode of solar-driven water splitting based on a wire-linked system shows ∼0.97 mA cm−2 of current density, and can split water under zero-bias conditions. Enhancement of the PEC device by accelerating electron and hole transport and broadening the diffusion length using photosensitizer materials while avoiding typical recombination with a thin passivation layer was achieved. The charge transport mechanism through combining experimental results in half and overall water splitting reactions is proposed. The success of such efficient multi-layered heterojunction photoelectrodes is essential for the future development of green energy harvesting devices.

Maternal RNA/protein degradation and zygotic genome activation (ZGA), occurring during maternal-to-zygotic transition (MZT), are the first essential events for the development of pre-implantation embryos. Previously, we have shown the importance of the ubiquitin-proteasome system (UPS) for initiation of minor ZGA at the 1-cell stage of mouse embryos. However, little is known about the mechanism of involvement of the UPS-degraded maternal proteins in ZGA. In this study, we investigated the effect of inhibiting maternal protein degradation by the reversible proteasome inhibitor, MG132, on post-implantation development and ZGA regulation during early cleavage stages. Our study revealed that zygotic transcription by RNA polymerase II (Pol II) at the 1-cell stage was delayed and the full-term development was affected by transient proteasome inhibition during 1 to 9 h post-insemination (hpi). Furthermore, we found that the transient inhibition of proteasome activity at the 2-cell stage delayed the onset of transcription of some major ZGA genes. These results support the model hypothesizing the requirement of sequential degradation of maternal proteins by UPS for the proper onset of ZGA and normal progression of MZT in early mouse embryos.

The radioisotope 117mSn has recently attracted considerable attention because of its application in theranostics and its imaging using 159-keV γ-photons. In this study, we developed a target system that yielded 117mSn via a 116Cd(α, 3n)117mSn nuclear reaction. A separable Pt substrate was utilized to prepare the enriched 116Cd target to be irradiated, and the enriched 116Cd in a cadmium acetate solution was electroplated onto the Pt substrate. The substrate was thermally analyzed via ANSYS simulations, and the plating thickness was optimized through calculations with TALYS code. The production of 117mSn was confirmed through the emission measurement of inherent gamma rays.

We report the rational design and fabrication of earth-abundant, visible-light-absorbing Cu2ZnSnS4 (CZTS) nanoparticle (NP) in situ sensitized S doped TiO2 nanoarchitectures for high-efficiency solar water splitting. Our systematic studies reveal that these nanoarchitectures significantly enhance the visible-light photoactivity in comparison to that of TiO2, S doped TiO2, and CZTS NP sensitized TiO2. Detailed photoelectrochemical (PEC) studies demonstrate an unprecedented enhancement in the photocurrent density and incident photon to electron conversion efficiency (IPCE). This enhancement is attributed to the significantly improved visible-light absorption and more efficient charge separation and transfer/transport, resulting from the synergistic influence of CZTS NP sensitization and S doping, which were confirmed by electrochemical impedance spectroscopy (EIS). Moreover, density functional theory (DFT) calculations supported by the experimental evidence revealed that the gradient S dopant concentration ...

Earth-abundant, copper–zinc–tin–sulfide (CZTS), kesterite, is an attractive absorber material for thin-film solar cells (TFSCs). However, the open-circuit voltage deficit (Voc-deficit) resulting from a high recombination rate at the buffer/absorber interface is one of the major challenges that must be overcome to improve the performance of kesterite-based TFSCs. In this paper, we demonstrate the relationship between device parameters and performances for chemically deposited CdS buffer/CZTS-based heterojunction TFSCs as a function of buffer layer thickness, which could change the CdS/CZTS interface conditions such as conduction band or valence band offsets, to gain deeper insight and understanding about the Voc-deficit behavior from a high recombination rate at the CdS buffer/kesterite interface. Experimental results show that device parameters and performances are strongly dependent on the CdS buffer thickness. We postulate two meaningful consequences: (i) Device parameters were improved up to a CdS buff...

We developed a design for a 6 MeV X-band linear accelerator for radiation therapy in a dual-head gantry layout. The dual-head gantry has two linacs that can be operated independently. Each X-band linac accelerates electron bunches using high-power RF and generates X-rays for radiation therapy. It requires a versatile RF system and pulse sequence to accomplish various radiation therapy procedures. The RF system consists of 9.3 GHz, 2 MW X-band magnetron and associated RF transmission components. A test linac was assembled and operated to characterize its RF performance without beam. This paper presents these results along with a description of the gantry linacs and their operational requirements.

The formation of secondary phases in kesterite-based solar cells plays a critical role, affecting the performances of devices primarily due to the open circuit voltage deficient characteristics. Systematic studies of the phase evolution pathways and the formation of secondary phases in kesterite thin films are desirable. In this paper, the phase evolution pathways and the formation of secondary phases in kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin films during thermal treatment of sputtered Cu-Sn-Zn metallic precursors have been studied using high-resolution X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). A possible phase evolution process for the kesterite thin films is proposed based on the experimental observations. The Cu-Sn-Zn metallic precursor thin films were prepared using the sputtering technique followed by thermal treatments at different temperatures ranging from 250 °C to 580 °C in a chalcogen atmosphere. XRD and Raman characterizations of the thin films annealed under chalcogen atmospheres indicated that the precursor thin films were completely transformed to the CZTS and CZTSe kesterite phases above 500 °C. However, the TEM analysis of the thin films annealed above 450 °C revealed Cu-based secondary phases. The formation of phase pure CZTS and CZTSe kesterites was observed at annealing temperatures above 500 °C. Based on the experimental observations, the phase evolution pathways for the formation of kesterite and secondary phases from metallic precursors are proposed in this paper.

The development of solution-processable routes as well as compounds consisting of earth abundant elements is highly desirable to reduce the fabrication cost. Recently, kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) have attracted great attention for photoelectrochemical (PEC) water splitting owing to their suitable low-cost, earth-abundancy and suitable band gap energy. However, the environmentally benign synthesis of high-quality CZTS NCs without toxic solvents remains elusive. Here, a green chemistry approach employing vegetable oil as a non-toxic solvent for the synthesis of monodisperse and size-tunable CZTS NCs is introduced for the first time. Additionally, the relationship between the abnormal size behavior of the CZTS NCs and the degree of decomposition in the vegetable oil using electrospray ionization mass spectrometry (ESI-MS) measurements is elucidated for the first time. As a conceptual strategy, a ternary abundant compound based heterojunction nanostructure for efficient solar water splitting by introducing CZTS NCs onto 5 nm Zn(O,S) passivated layer/hydrothermally grown TiO2 nanorod arrays (TNRs) is designed and developed. Remarkably, this ternary CZTS NCs/Zn(O,S)/TNR photoelectrode shows a photocurrent density as high as 15.05 mA cm−2 at 1.23 V (vs. the NHE), which is the highest ever for previously reported CZTS NC-based photoelectrodes. The reasons for the enhanced PEC performance are discussed in detail based on different PEC characterizations. More importantly, this work reflects the sophistication of eco-friendly solution phase synthesized CZTS NCs without using any toxic chemicals as an earth abundant sensitizer and constitute a new paradigm towards the enhanced PEC performance with quantum dot based hetero-nanostructures.

The semiconductor Cu2ZnSnS4 (CZTS) is a promising sustainable photovoltaic material and colloidal dispersions of wurtzite or kesterite CZTS nanocrystals are often used to make thin polycrystalline films for solar cells. This requires control of the nanocrystal phases via the synthesis. We studied the microwave-assisted solvothermal synthesis of CZTS nanocrystals from metal salts and thiourea in ethylene glycol in the presence of various excess sulfur sources. Relative fractions of the kesterite and wurtzite phases depend on the excess sulfur source, the oxidation state of Sn, and the sulfur-to-total-metal -cation (S : M) ratio used in the synthesis. When the excess sulfur source contains an amino group, a Zn–Sn intermediate forms and allows the CZTS phase to be varied between kesterite and wurtzite via the Sn initial oxidation state and S : M ratio. When the excess sulfur source contains an amino group, synthesis using Sn(II) salts and low S : M (1.9) favors the formation of the wurtzite phase, whereas synthesis using high S : M ratio (>4) favors the formation of the kesterite phase. Only the kesterite phase is obtained when Sn(IV) reagent is used, regardless of S : M ratio. When the excess sulfur source does not have an amino group, only the wurtzite phase is obtained under the conditions studied, regardless of the oxidation state of the Sn precursor or the S : M ratio; in these cases, the Zn–Sn intermediate does not form and the precursor to wurtzite appears to be copper sulfide.

An array of one dimensional (1D) TiO 2 nanorods (TONRs) has been regarded as an attractive candidate for electrochemical energy conversion and as storage device due to its large surface area, effiective light scattering, and undisturbed charge transport pathway. However, the high defect/trap densities on surface of the nanostructured morphology and architecture may generally hinder the performance enhancement by providing electron-hole recombination sites. Hence, the surface passivation of nanoarchitectures based photoelectrodes has recently received much attention as an effective strategy to enhance the charge-separation and charge-transfer processes in photoelectrochemical (PEC) water splitting devices. In particular, a coating layer with narrowing band gap materials can promote enhanced light harvesting in the UV–vis region as well as surface passivation, directly supplying a driving force for charge separation and charge transfer due to band alignment. In this paper, the surface of TONRs were passivated by 10 and 30 nm thick Zn(O,S) layers with a relatively narrow band gap using an atomic layer deposition technique to modulate the thickness exactly. The 10 nm Zn(O,S)/TONR array exhibits a significantly enhanced photocurrent density (J sc ) of 5.94 mA/cm 2 at 1.23 eV vs NHE and an incident photon-to-electron conversion efficiency (IPCE) of 49% at 374 nm compared with that of TONR arrays (J sc of 1.99 mA/cm 2 at 1.23 eV vs NHE and an IPCE of 20% at 380 nm). However, the PEC performance is worse in the 30 nm Zn(O,S)/TONR arrays, showing a J sc of 3.09 mA/cm 2 at 1.23 eV vs NHE and an IPCE of 29% at 374 nm. To clearly demonstrate these PEC behaviors, the TONR and Zn(O,S)/TONR arrays were characterized by electrochemical impedance spectroscopy (EIS), open circuit voltage decay (OCV) measurement, and X-ray photoelectron spectroscopy (XPS). The above mentioned characterizations indicate that the enhanced PEC performance of the 10 nm Zn(O,S)/TONR array resulted from the (i) increased light harvesting in the UV–vis region, (ii) lower charge transfer resistance and (iii) high value of valence band offset (VBO, −1.44 eV) and conduction band offset (CBO, −1.2 eV) than those of the TONR. However, the deterioration of J sc in the 30 nm Zn(O,S)/TONR array is attributed to the negative value of VBO (-0.13 eV) and positive value of CBO (+0.27 eV), as well as the higher charge transfer resistance to the electrolyte than that of the TONR arrays, despite of the improved light absorption in the visible region. The photocurrent densities of 10 nm Zn(O,S)/TONR and 30 nm Zn(O,S)/TONR photocathodes decay to 4.718 mA/cm 2 (5.90 mA/cm 2 at 0 min) and 2.212 mA/cm 2 (3.03 mA/cm 2 at 0 min) after 90 min, respectively, they retain of about ∼ 80% and 70% of its original values. These experimental results and discussions not only provide the physical insights into the surface passivation effect and band alignment but also can open a promising route to design the thin passivation layer having the narrowing band gap energy (1.0 eV ∼ 2.5 eV) on the 1D TiO 2 nanostructure for further enhanced performance and realization of a TiO 2 based PEC system.

The structural, electrical, chemical, and optical properties of ternary Zn(O,S) thin films formed by atomic layer deposition (ALD) were investigated. It was revealed that the film׳s characteristics were highly influenced by the O/(O+S) ratio. The n-type Zn(O,S) layer was applied to both S-rich and Se-rich Cu2ZnSn(S,Se)4 (CZTSSe) absorbers as an alternative buffer layer to conventional CdS. The device performance relationship to the O/(O+S) ratio was examined. The highest power-conversion efficiency (PCE) of 2.75% and 3.30% was achieved using an actual O/(O+S) ratio of ~0.67 in the buffer layer for S-rich and Se-rich CZTSSe solar cells, and these PCEs correspond to 77% and 67% of the standard CdS-based solar cells, respectively. Further improvement in Se-rich CZTSSe was demonstrated by using NH4OH solution instead of pure H2O as oxygen source during ALD process. The dependence of the solar cell performance on the O/(O+S) ratio was investigated using dark current density–voltage (J–V), external quantum efficiency (EQE), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX).

This paper describes an approach to using the successive ionic adsorption and reaction (SILAR) method for the synthesis of Cu 2 ZnSnS 4 (CZTS), a highly promising thin film absorber material. This approach involves the preparation of stacked precursor thin films of Cu 2 SnS 3 and ZnS by using the SILAR method with different stacking orders, such as Mo/Cu 2 SnS 3 /ZnS (CZTS-A) and Mo/ZnS/Cu 2 SnS 3 (CZTS-B). These stacked precursor films were sulfurized at 575 °C for 1 h in a H 2 S (5%) + N 2 (95%) atmosphere. The characteristics of the CZTS thin films prepared using stacked sulfide precursors are strongly dependent on the stacking orders in the precursor thin films. The influence of different precursor stacking orders on the structural, compositional, morphological and optical properties as well as the photoelectrochemical (PEC) performance of the CZTS thin films were studied. The best PEC performance of 1.81% was obtained with a maximum J sc of 11.68 mA/cm 2 , V oc of 0.42 V and FF of 0.37 for the CZTS thin films based on the stacking order of Mo/ZnS/Cu 2 SnS 3 .

In the development of low-cost, efficient, and environmentally friendly thin-film solar cells (TFSCs), the search continues for a suitable inorganic colloidal nanocrystal (NC) ink that can be easily used in scalable coating/printing processes. In this work, we first report on the colloidal synthesis of pure wurtzite (WZ) Cu2SnS3 (CTS) NCs using a polyol-mediated hot injection route, which is a nontoxic synthesis method. The synthesized material exhibits a random distribution of CTS nanoflakes with an average lateral dimension of ∼94 ± 15 nm. We also demonstrate that CTS NC ink can be used to fabricate low-cost and environmentally friendly TFSCs through an ethanol-based ink process. The annealing of as-deposited CTS films was performed under different S vapor pressures in a graphite box (volume; 12.3 cm3), at 580 °C for 10 min using a rapid thermal annealing (RTA) process. A comparative study on the performances of the solar cells with CTS absorber layers annealed under different S vapor pressures was cond...

A simple and eco-friendly method of solution processing of Cu2SnS3 (CTS) absorbers using an aqueous precursor solution is presented. The precursor solution was prepared by mixing metal salts into a mixture of water and ethanol (5:1) with monoethanolamine as an additive at room temperature. Nearly carbon-free CTS films were formed by multispin coating the precursor solution and heat treating in air followed by rapid thermal annealing in S vapor atmosphere at various temperatures. Exploring the role of the annealing temperature in the phase, composition, and morphological evolution is essential for obtaining highly efficient CTS-based thin film solar cells (TFSCs). Investigations of CTS absorber layers annealed at various temperatures revealed that the annealing temperature plays an important role in further improving device properties and efficiency. A substantial improvement in device efficiency occurred only at the critical annealing temperature, which produces a compact and void-free microstructure with large grains and high crystallinity as a pure-phase absorber layer. Finally, at an annealing temperature of 600 °C, the CTS thin film exhibited structural, compositional, and microstructural isotropy by yielding a reproducible power conversion efficiency of 1.80%. Interestingly, CTS TFSCs exhibited good stability when stored in an air atmosphere without encapsulation at room temperature for 3 months, whereas the performance degraded slightly when subjected to accelerated aging at 80 °C for 100 h under normal laboratory conditions.

As the semiconductor manufacturing industry develops into the cutting-edge technology, the thick and high etch resistant material is required. Amorphous carbon layer (ACL), currently widely-used deposition-type film, can meet the requirement for etch resistance, but it has intrinsic problems such as darkness, defect control difficulty and low throughput which give limits to its further application. In order to overcome these problems, a novel thick spin-on carbon hardmask (SOH) is introduced in this paper. We designed the material from molecular level to achieve high etch resistance, good optical property, long shelf life and high thickness. Up to 3 micron-thick films with high transparency and etch resistance were successfully fabricated by spin-coating process. With long-enough shelf life for usage, we expect that this novel SOH can expand the possibility of spin-on material.