CuxS Films Research Articles

CuxS films as photoelectrodes for visible-light water splitting

Copper sulfides are appealing semiconductors for optoelectronics applications requiring visible-light activity, such as solar water splitting, due to their relatively low band gaps and earth-abundance. This study investigates the effect of deposition conditions, including substrate temperature and background gas pressure, on the characteristics and photoelectrochemical performance of copper sulfide (CuxS) films grown by pulsed laser deposition (PLD) on Si (100) substrates. The results reveal that varying the deposition parameters influences the crystalline phases, morphology, and optoelectronic properties of the films. For deposition at room temperature, the films exhibited covellite CuS phase, while elevated deposition temperatures (250 °C and 500 °C) led to the formation of Cu1.8S and Cu2S phases, resulting in narrowing of the band gap, with the increased temperature also enhancing the film crystallinity and surface roughness. As a result of the changes in film morphology and crystal structure, photocurrent density magnitudes increased with higher deposition temperatures, reaching 0.747 mA/cm2 at −0.8 V for films deposited at 500 °C under vacuum, at least an order of magnitude higher than reported in comparable previous studies of the photoelectrochemical performance of CuxS. Background gas pressure only slightly affected the photocurrent density, with changes in photoactivity also correlating with changes in film roughness and band gap. The results demonstrate the good visible-light activity and behavior of CuxS as a stand-alone photoelectrode material, with tunability based on the fabrication conditions, suggesting their potential use in photoelectrochemical and other solar energy conversion applications.

Synthesis of copper sulfide (CuxS) films by one-step thermal reduction of copper formate–amine–sulfur complex pastes with low sulfur ratios

A one-step thermal-reduction method was used to synthesize copper sulfide (CuxS, x = 1–2) films using copper formate–sulfur–amine pastes with low sulfur ratios (sulfur/copper formate = 0.5–1.0). The synthesized films were mixtures of Cu + Cu2S, Cu2S + Cu1.8S, or Cu1.8S + CuS, depending on the sulfur ratio. Cu1.8S alone films were synthesized from the paste with a sulfur ratio of 0.75 at 200 °C. The films comprised single-crystal nanoparticles with a size of 10–20 nm, which were covered with excess sulfur and agglomerated to form pillar-like structures. The amount of excess sulfur increased with an increasing sulfur ratio in the paste. The formation of pillar-like structures was due to the individual nanoparticles being connected by excess sulfur and the evaporation of CO2, H2O, and amine during the thermal reduction of copper formate.

Flexible stretchable electrothermally/photothermally dual-driven heaters from nano-embedded hierarchical CuxS-Coated PET fabrics for all-weather wearable thermal management

The multifunctional photoelectronic devices are recently attracting much more attention due to their potential enlarged applications. The flexible stretchable electrothermally/photothermally dual-driven heaters for all-weather wearable thermal management are presented in this work with nano-embedded hierarchical CuxS-coated PET fabrics. Herein, the hierarchical nano-embedded CuxS film is fabricated via a simple chemical bath method for high electrical conductivity and highly efficient inelastic collision of electro/photo-generated carriers. The hierarchical nano-embedded CuxS morphology produces the low sheet resistance of 1.26 Ω sq-1 and the super low total heat transfer coefficient of 3.256 × 10-5 W/oC·mm2, which lead to the high-efficient electro/photo-dual-driven heating effect in the CuxS@PET fabrics. The saturated temperature on the as-fabricated flexible wearable heaters reaches up to 172 °C. The thermal conversion devices also bear the excellent stability, reproducibility, stretchability, controllability and corrosion-resistant characteristics. Interestingly, their excellent thermal conversion performance could be achieved by freely exchanging the driving power sources, such as electricity-supplying equipment, 635-nm laser, infrared physiotherapy lamp and solar simulator, which provides a necessary precondition for the all-weather applications of flexible wearable heaters. The as-fabricated electro/photo-dual-driven heaters on the CuxS@PET fabrics have the promising applications in wearable electronics, all-weather self-heating facilities, out/in-vivo physiotherapy, and so on.

Deposition and properties of mixed molybdenum sulfide (MoS2) and copper sulfide (CuxS) films on glass surface using elemental sulfur as a precursor

Mixed molybdenum sulfide (MoS2) and copper sulfide (CuxS) materials were synthesized on glass slides as a model substrate by successive ionic layer adsorption and reaction method using elemental sulfur as a sulfur source and solutions of copper (II/I) and molybdenum (IV) salts. X-ray diffraction data showed the presence of copper sulfides (anilite Cu7S4 and djurleite Cu31S16 phases), molybdenum disulfide and molybdenum oxide with adjustable crystalline phase composition dependent on the precursor exposure time and reaction temperature. Scanning electron microscopy images showed that the surface had a homogenous layer distribution at lower temperatures/short exposures and comprised of ~1 μm particles. X-ray photoelectron spectroscopy showed no oxidized sulfate (SO42−) compounds present on the sample surface while a thin MoO3 layer was found to cover the sample surface. Optical ultraviolet-visible spectroscopy showed mixed layers formed, containing optical properties of both MoS2 and CuxS. After annealing in an N2 atmosphere at 100 °C, the sample was composed primarily of MoS2 and copper sulfides in the crystalline phase with minimal residual S8. Usability of this mild mixed metal sulfide thin film preparation method on supports for sour natural gas catalyst synthesis is also discussed.

Impact of TiO2 layer formed on CuxS Films on the Photoelectrochemical Water Reduction Process

Solar radiation is the main source of renewable energy capable of satisfying the increasing energy demand without contributing to climate changes using fossil fuels. Energy harvesting from solar radiation requires innovation in materials with appropriate functional properties to produce chemical energy. This study aims to contribute in that sense. It reports the synthesis and characterization of photocathodes for hydrogen evolution based on TiO2/CuxS films formed on FTO glass. CuxS is prepared by electrodeposition of copper, followed by chalcogenide formation through immersion in a sulfide source solution and then modified by heat treatment. A TiO2 layer is deposited on CuxS film to favor its stability and charge carrier separation process. The calcination of bare CuxS film causes the formation of a mixture of copper oxides. TiO2 film acts as an effective protector, preserving a larger proportion of Cu chalcogenide species by preventing the complete oxidation, without considerably varying the reducing power of photogenerated electrons in the films. TiO2 layer favors the absorption of low energy photons and increases the photocurrent, diminishing electron-hole recombination probability.

Effect of laser fluence on structural and optical properties of CuxS films grown by pulsed laser deposition at different wavelengths

CuxS thin films were grown onto soda-lime glass substrates by pulsed laser deposition at two different wavelengths: 1064 and 532 nm. X-ray diffraction, Raman and UV–vis spectroscopies were used to characterize the CuxS films. Results are presented as a function of laser fluence. XRD patterns indicate that covellite and chalcocite phases were obtained. Raman spectra showed that chalcocite is the predominant phase in the crystalline samples. Optical band gap values are between 2.29 and 2.74 eV for ablation with 1064 nm wavelength; meanwhile, for 532 nm band gap values varied from 2.24 to 2.66 eV; which are in the range of expected values for CuxS films. At 1064 nm and 4.4 J cm−2 sample presented the highest optical absorbance in the visible range, which corresponds to the highest thickness. These are the best growth parameters for CuxS films in order to be used as absorber films for solar cells applications.

Low-cost semi-transparent copper sulfide electrode for indium-tin-oxide-free perovskite solar cells

Development of transparent electronics has been hindered by the lack of stable p-type transparent conductive electrodes. Herein we report the fabrication of p-type copper sulfide thin films (CuxS) used for the first time as semitransparent electrode used as an example in inverted-planar perovskite solar cells (PSCs). The resulting hole-transporting-material-free and indium-tin-oxide-free (ITO-free) device showed an unprecedented 5.9% efficiency (PCE). Morphological, structural and optoelectronic analysis of the CuxS films were accomplished to correlate the photovoltaic behavior of the obtained PSCs. In particular, covellite (CuS) and digenite (Cu1.8S) crystal phases were identified in the resulting CuxS film. The p-type CuxS semitransparent electrode exhibited high 1094 S cm−1 electrical conductivity comparable to state-of-the-art transparent conductive electrodes (TCE). Although the CuxS electrode exhibits a relatively low bandgap around 2.7 eV, the spectral response of the devices demonstrates that the related optical loss happens just in the blue and UV region of the visible spectrum leading to a reduction of the photocurrent below 10%. On the other hand, surface photovoltage analysis of the grown perovskite indicates that the CuxS electrode induces an optimal band alignment in the perovskite surface while trap states were favored by using CuxS regarding ITO. These results suggest that photovoltaic parameters of CuxS-based PSCs can be still improved by a better control of perovskite growing. Finally, material cost per square meter (US$/m2) was estimated for CuxS electrodes and an impressive reduction of 77.6% was observed compared to commercial ITO. These results highlight the potential application of CuxS film as low-cost, non-toxic and scalable p-type semitransparent electrode in PSCs and other optoelectronic devices.

Parameter-controllable microchannel reactor for enhanced deposition of copper sulfide thin films

A microchannel reactor was designed and fabricated based on the unique fluid-flow and mass transfer characteristics in a closely parallel channel for the deposition of copper sulfide (CuxS) thin films. The configuration of the microchannel allows the flow pattern to be confined uniformly across the channel width and length, thereby resulting in a uniform deposited thin film covering the whole surface of the substrate. A parametric study of the deposition of CuxS thin films was performed, including the effects of deposition time (2–10min), flow rate (2–6ml/min) and reaction temperature (60–80°C). It was observed that the basic characteristics of CuxS films, such as morphology, film thickness, film composition and optical band gap, were highly affected by all deposition parameters. We were able to attain smooth, dense and adherent CuxS film with homogeneous grains at a high growth rate of 1.8μm/h, by optimizing the controllable parameters. The optimized condition was at temperature of 80°C, flow rate of 6ml/min and deposition time of 4min. The results showed that the film formation by heterogeneous nucleation and growth on the substrate is promoted over homogeneous reaction in the solution phase, which is strongly due to the incorporation of the optimal channel design in a micro-scale structure together with the controlled deposition parameters. This method can overcome the issue of the deposition in limited area and can be scaled for large-area substrates with good uniformity of CuxS films.

Non-toxic growth of CuxS thin films in alkaline medium by ammonia free chemical bath deposition

CuxS thin films were deposited on commercial glass substrates at different temperatures by an ammonia-free chemical bath deposition process. The deposition process is based in a copper chloride- sodium citrate- thiourea system. The pH value in the reactive solution was adjusted at 10 by addition of KOH and buffer solution. In order to investigate the effect of the deposition temperature and time, four reaction baths were prepared and set at temperatures 25, 40, 55 and 70 °C. The deposited films were studied by X-ray diffraction, Raman spectroscopy, 3D optical microscopy, energy dispersive X-ray spectroscopy, electron probe X-ray microanalysis, UV–vis spectroscopy and two-points probe electrical measurements. The chemically deposited CuxS films showed good adherence to the substrate, homogeneity, metallic luster and light reddish-brown appearance. The thickness of the films varied in the range of 40–80 nm, depending on the deposition conditions. The X-ray diffraction revealed that the films present amorphous nature, excepting those deposited at the highest temperature, which had CuS covellite crystalline structure. The chemical composition of the films exhibited the presence of the covellite phase with excess of sulphur atoms in all cases. The electrical analysis showed a strong decrease in the resistivity with increasing the deposition temperature with values in the range from 106 to 10−2 Ωcm.

Facile fabrication of p-type CuxS transparent conducting thin films by metal sulfide precursor solution approach and their application in quantum dot thin films

We present a facile route for the fabrication of P-type CuxS transparent and conducting thin films (TCTFs) using copper (I) oxide and butyl-dithiocarbamic acid as precursors by pulling method on glass. The as-deposited highly conductive crystalline CuxS films showed high carrier concentration (∼3.11 × 1022 cm−3), low electrical resistivity (∼1.02 × 10−4 Ω cm) and conclusive p-type conduction. X-ray diffraction studies showed high crystallinity, and the optical transmission spectra in UV–vis–NIR region of such films were recorded, indicating that the transparency was over 75% with a band gap of 1.52 eV. The room-temperature sheet resistance increased from 9.9 to 302.4 Ω sq−1 with increasing baking temperature. The CuxS/quantum dot bifacial thin films have been fabricated, and the experimental results indicated that luminescent, transparent, and conductive CuxS/Cu-doped ZnyCd1-yS thin films have a very high potential application in thin film solar cells.

The synthesis of CuxS from Cu layers by low pressure plasma processing

A new method of converting Cu layers to CuxS on glass at low pressure using an electron cyclotron resonance plasma and SF6 gas is presented. The process operates at low temperatures and short time scales. Trends in film crystallinity and morphology are identified in relation to process time and temperature. These show that sulphurisation is most likely complete within 10 min and that the sulphur content of the films reduces as the conversion temperature is increased from 473 to 623 K. Optical measurements show that the films have a direct bandgap of ~2.5 eV which is consistent with published values for CuxS films grown by other techniques. Analysis by SEM has revealed that the films possess a complicated structure of platelets covering a denser underlying film. This may account for the differences in observations made by XRF and Raman spectroscopy, which both indicated a mixture of CuS and Cu2S, and X-ray diffraction which predominantly showed CuS.

CuxS counter electrodes in-situ prepared via the sulfidation of magnetron sputtering Cu film for quantum dot sensitized solar cells

The nanosheet-structured CuxS thin films used as counter electrodes (CEs) for CdS/CdSe quantum dot sensitized solar cells (QDSSCs) have been in situ prepared via the sulfidation of Cu nanoparticles deposited on F-doped SnO2 glass (FTO glass) substrate by magnetron sputtering method. The thickness of the deposited Cu film affects the morphology and thickness of the obtained CuxS films. The CuxS nanosheet films have good adhesion with FTO glass and the surface exhibits uniform morphology. The characteristics of QDSSCs are studied in more detail by photocurrent-voltage performance measurements, incident photon-to-current conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS). The CuxS on FTO glass (CuxS/FTO) CEs show much higher power conversion efficiency (PCE) and IPCE than those of the Pt on FTO (Pt/FTO) CE because of their superior carrier mobility and electro-catalytic ability for the polysulfide redox reactions. Based on an optimal CuxS film thickness of 2.7 μm obtained by the sulfidation of the Cu film thickness of 300 nm on FTO, the best photovoltaic performance with PCE of 3.67% (Jsc = 16.47 mA cm−2, Voc = 0.481 V, FF = 0.46) under full one-sun illumination is achieved.

Deposition of ultra thin CuInS2 absorber layers by ALD for thin film solar cells at low temperature (down to 150 °C)

Two new processes for the atomic layer deposition of copper indium sulfide (CuInS2) based on the use of two different sets of precursors are reported. Metal chloride precursors (CuCl, InCl3) in combination with H2S imply relatively high deposition temperature (Tdep = 380 °C), and due to exchange reactions, CuInS2 stoechiometry was only achieved by depositing In2S3 layers on a CuxS film. However, the use of acac- metal precursors (Cu(acac)2, In(acac)3) allows the direct deposition of CuInS2 at temperature as low as 150 °C, involving in situ copper-reduction, exchange reaction and diffusion processes. The morphology, crystallographic structure, chemical composition and optical band gap of thin films were investigated using scanning electronic microscope, x-ray diffraction under grazing incidence conditions, x-ray fluorescence, energy dispersive spectrometry, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. Films were implemented as ultra-thin absorbers in a typical CIS-solar cell architecture and allowed conversion efficiencies up to 2.8%.

Ionic Liquid Electrochemical Synthesis of Earth Abundant Monophase Chalcostibite p-CuSbS2 Photo-absorber Thin films for Heterojunction Solar Cells With n-ZnO

ABSTRACTSingle step synthesis of monophase CuSbS2 thin films by electro-deposition in ionic liquid electrolyte based on choline chloride and urea (ChCl:U) eutectic mixture is described. The formation of binary CuxS and SbxSy film phases using CuCl2 and SbCl3 precursors along with Na2S2O3 as sulfur source in ChCl:U are established as -0.59 V and -0.36 V vs. Pt, respectively by cyclic voltammetry and used to optimize CuSbS2 thin films growth potential and precursor composition. CuSbS2 films deposited at -0.65 V vs Pt with 1:1 Cu to Sb precursor ratio at 80⁰C are highly crystalline in chalcostibite orthorhombic structure. Deviant Cu/Sb ratio at 1:0.71 and 1:1.4 reveal inclusion of Cu3SbS3 and Sb2S3, respectively. Direct 1.65 eV band gap for single phase CuSbS2 film and with inclusive secondary phases at 1.73±0.1 eV and 2.13 eV is observed. As-deposited CuSbS2 films are p-type and n-p hetero-junction device in the n-ZnO/p-CuSbS2/Ag structure shows rectifying I-V curves and dependence on the CuSbS2 film growth conditions.

Enhanced electrocatalytic activity of vacuum thermal evaporated CuxS counter electrode for quantum dot-sensitized solar cells

Vacuum thermal evaporated CuxS (VTE-CuxS) film on fluorine-doped tin oxide substrate has been investigated as counter electrode (CE) for quantum dot-sensitized solar cells (QDSCs) with polysulfide electrolyte. The photovoltaic parameters of QDSCs show an obvious dependence on the annealing time of CuxS film, and the maximum power conversion efficiency of 3.16±0.05% under one sun illumination (100mWcm−2, AM 1.5G) was obtained when the VTE-CuxS CE was annealed at 270°C for 300s (VTE-CuxS-300s CE). Electrochemical impedance spectroscopy, Tafel polarization, and cyclic voltammetry measurements have been employed to investigate the electrocatalytic activity of VTE-CuxS-300s CE. The electrocatalytic activity of the VTE-CuxS-300s CE is much higher than that of Pt CE, and is slightly higher than that of Cu2S CE in situ prepared on brass sheet. In particular, VTE-CuxS-300s CE holds high diffusion velocity of S2−/Sn2− in polysulfide electrolyte, and the stability of its electrocatalytic activity in polysulfide electrolyte is better than that of Pt and Brass-Cu2S CEs obviously.

Electrocatalytic activity of chemically deposited CuxS thin film for counter electrode in quantum dots-sensitized solar cells

The compact (c-CuxS) and the porous (p-CuxS) with particle decorated films of coppers-ulfidearesynthesized using a chemical bath deposition technique, and the films are characterized using electrochemical techniques. In addition, the chemically deposited CuxS films are investigated as a counter electrode in quantum dots-sensitized solar cells (QSSCs). The available redox active reaction sites of the p-CuxS film are found to be 57.9% higher than those available in the c-CuxS film. From the electrochemical impedance spectroscopy, the effective diffusion coefficients of the polysulfide electrolyte in the c-CuxS and p-CuxS films are estimated to be 3.67 × 10−5 and 6.35 × 10−5 cm2 s−1, respectively. These results can be ascribed to the improvement in the available redox active reaction sites and the electrocatalytic activity of the CuxS counter electrode. As compared to the c-CuxS film, the p-CuxS film as a counter electrode exhibits an enhanced photovoltaic performance of the QSSCs with the power conversion efficiency of 3.17%, short-circuit current of 11.89 mA c−m2, open-circuit voltage of 0.50 V, and fill factor of 53.29. The improved performance of the QSSCs is ascribed to the improvements on the available redox active reaction sites, electrocatalytic activity and the diffusion coefficients, which are directly related to the surface morphology of the sulfide films.

The influence of the deposition time on morphological and optical properties of Cu x S films deposited on polypropylene substrate

Copper sulfide (Cu x S) films deposited on polypropylene substrate were obtained by chemical bath deposition (CBD) method. The influence of the deposition time on the morphology of Cu x S films was studied by means of scanning electron microscopy. We have found that the average particles dimension increased from 37 to 49 nm with the increase of deposition time from 20 to 30 minutes. The study of optical properties of the copper sulfide films was carried out based on optical transmission spectra recorded in the 400–1000 nm wavelength range. The optical constants, such as refractive index, extinction coefficient and dielectric constant as well as electrical and optical conductivity of Cu x S films were calculated. The obtained values are in accordance with the ones reported in the literature:We have shown that both, morphological and optical properties of Cu x S films are strongly affected by the deposition time.

P-type CuxS thin films: Integration in a thin film transistor structure

CuxS thin films, 80nm thick, are deposited by vacuum thermal evaporation of sulfur-rich powder mixture, Cu2S:S (50:50wt.%) with no intentional heating of the substrate. The process of deposition occurs at very low deposition rates (0.1–0.3nm/s) to avoid the formation of Cu or S-rich films. The evolution of CuxS films surface properties (morphology/roughness) under post deposition mild annealing in air at 270°C and their integration in a thin film transistor (TFT) are the main objectives of this study. Accordingly, Scanning Electron Microscopy studies show CuxS films with different surface morphologies, depending on the post deposition annealing conditions. For the shortest annealing time, the CuxS films look to be constructed of grains with large dimension at the surface (approximately 100nm) and consequently, irregular shape. For the longest annealing time, films with a fine-grained surface are found, with some randomly distributed large particles bound to this fine-grained surface. Atomic Force Microscopy results indicate an increase of the root-mean-square roughness of CuxS surface with annealing time, from 13.6 up to 37.4nm, for 255 and 345s, respectively. The preliminary integration of CuxS films in a TFT bottom-gate type structure allowed the study of the feasibility and compatibility of this material with the remaining stages of a TFT fabrication as well as the determination of the p-type characteristic of the CuxS material.

Photoelectrochemical sensing of Cu2+ ions with SnO2/CdS heterostructural films

We report here on preparation of SnO2/CdS heterostructural films on fluorine-doped tin oxide (FTO) substrates and their application in selective sensing of Cu2+ ions by photoelectrochemistry. Films of SnO2 particles were first synthesized by thermal decomposition of SnSO4 that was spreaded on the FTO substrates by solution evaporation, and SnO2/CdS heterostructural films were then obtained by performing successive ionic layer adsorption and reaction (SILAR) on the SnO2 films. The anodic photocurrent density on the prepared FTO/SnO2/CdS films was as high as 1.4mAcm−2 in 1M Na2SO3 solution under visible illumination due to effective light absorption and charge separation of the heterostructure. Cu2+ sensing was based on the interaction between Cu2+ and CdS by immersing the heterostructural film electrode into a Cu2+-containing sample for 5min. The binding of Cu2+ by S2− onto the heterostructural surface led to decrease in photocurrent on the FTO/SnO2/CdS/CuxS film electrode in the Na2SO3 solution, and the decrease extent of photocurrent depended on the Cu2+ concentration in the sample solution. The proposed photoelectrochemical device for the detection of Cu2+ ions can be easily fabricated with good selectivity, low detection limit (0.55μM), and acceptable detection range (1.00–38.0μM), which can be applied to detect Cu2+ ions in drinking water.

The combination of surface enhanced Raman spectroscopy and an ionic liquid as a model system to study the adhesion interface between sulfur and brass

The adhesion of steel cord to rubber is very important for the quality of reinforced rubber products, e.g. tyres. Therefore, steel cord is often plated with brass, which will lead to CuxS bonds after reaction with sulfur compounds in the rubber. A unique in‐situ analytical method has been developed to investigate the sulfur–brass interface: the sulfuring process has been simulated via a heating process in a water‐free transparent ionic liquid with added sulfur and the reaction at the brass‐coated steel cord has been monitored in real time with Raman spectroscopy. The grown CuxS film seems to be similar to the layers at the steel cord interface in real rubber materials. The model system can also be used to perform electrochemical measurements at the same time. The thickness of the CuxS layer has been estimated from the measured current during a cathodic stripping process. Copyright © 2013 John Wiley & Sons, Ltd.