Potentiostatic electrodeposition of cuprous oxide thin films for photovoltaic applications

Potentiostatic deposition of Cu₂O thin films on glass substrates coated with F-doped SnO₂ from an alkaline electrolyte solution (pH 12.5) containing copper (II) sulfate and lactic acid was studied for fabrication of a Cu₂O/Al-doped ZnO (AZO) heterojunction solar cell. The band gap of the electrodeposited Cu₂O films was determined by photoelectrochemical measurements to be around 1.9 eV irrespective of the applied potentials. The solar cells with a glass/FTO/Cu₂O/AZO structure were fabricated by sputtering an AZO film onto the Cu₂O film followed by deposition of an Al contact by vacuum evaporation. The highest efficiency of 0.603% was obtained with a Cu₂O film deposited at −0.6 V (vs. Ag/AgCl). This was attributed to better compactness and purity of the Cu₂O film than those of the Cu₂O films deposited at other potentials.     

Effect of electrodeposition and annealing of ZnO on optical and photovoltaic properties of the p-Cu2O/n-ZnO solar cells

Cu₂O/ZnO p–n heterojunction solar cells were fabricated by rf sputtering deposition of n-ZnO layer, followed by electrodeposition of p-Cu₂O layer. The different electrodeposition potentials were applied to deposit Cu₂O on ZnO. The particle size, crystal faces, crystallinity of Cu₂O is important factor which determine the p–n junction interface and consequently their effect on the performance of the heterojunction solar cell. It is observed that at −0.6 V, p-Cu₂O film generates fewer surface states in the interband region due to the termination of [1 1 0] resulting in higher efficiency (0.24%) with maximum particle size (53 nm). The bandgap of Cu₂O at this potential is found to be 2.17 eV. Furthermore, annealing of ZnO film was performed to get rid of deteriorating one and two dimensional defects, which always reduce the performance of solar cell significantly. We found that the solar cell performance efficiency is nearly doubled by increasing the annealing temperature of ZnO thin films due to increasing electrical conductance and electron mobility. Doping studies and fine tuning of the junction morphology will be necessary to further improve the performance of Cu₂O/ZnO heterojunction solar cells.     

Electrodeposited ZnO/Cu2O heterojunction solar cells

In this paper the fabrication and the characterization of heterojunction solar cells based on electrodeposited ZnO and Cu₂O is described. The effect of the electrodeposition conditions (pH and temperature) on the cell performance has been investigated. The cells made with a Cu₂O layer deposited at high pH (12) and moderate temperature (50 °C) have shown conversion efficiency as high as 0.41%.     

Effect of Al doped ZnO on optical and photovoltaic properties of the p-Cu2O/n-AZO solar cells

Metal oxide thin films have fared so well in the semiconductor industry because of their superior physical, electrical, and optical properties. The applications of these materials in solar cells, biosensors, biomedicine, supercapacitors, photocatalysis, luminous materials, and laser systems are becoming increasingly popular. In this study, the influence of Al concentration on Cu₂O/AZO heterojunction thin films was examined systematically. First, arrays of n-ZnO and AZO rods were produced on an ITO substrate using a hydrothermal technique at 140 °C. Then, using an alkaline cupric lactate solution, a thin films of p-Cu₂O were electrodeposited at 60 °C onto the ZnO arrays. The structure and morphology of the produced materials and the solar cells were studied using X-ray diffraction and scanning electron microscopy. The optical measurements demonstrate a shift in the absorption edge with increasing Al content. Solar cells have been created with a device structure of ITO/ZnO/Cu₂O/Al and ITO/Al-doped ZnO/Cu₂O/Al configurations. The power conversion efficiency (?) of the inorganic solar cell with 6% Al-doped ZnO is ? = 0.282%, which is greater than the ? of the ZnO-based solar cell (? = 0.17%).     

Open structure ZnO/CdSe core/shell nanoneedle arrays for solar cells

Open structure ZnO/CdSe core/shell nanoneedle arrays were prepared on a conducting glass (SnO₂:F) substrate by solution deposition and electrochemical techniques. A uniform CdSe shell layer with a grain size of approximately several tens of nanometers was formed on the surface of ZnO nanoneedle cores after annealing at 400°C for 1.5 h. Fabricated solar cells based on these nanostructures exhibited a high short-circuit current density of about 10.5 mA/cm² and an overall power conversion efficiency of 1.07% with solar illumination of 100 mW/cm². Incident photo-to-current conversion efficiencies higher than 75% were also obtained.     

Macroscopically uniform electrodeposited ZnO films on conducting glass by surface tension modification and consequent demonstration of significantly improved p–n heterojunctions

An alternative water–ethanol zinc nitrate solution is demonstrated to completely eliminate macroscopic defects that are normally prevalent in ZnO films electrochemically deposited from aqueous zinc nitrate solutions. The inclusion of 25% ethanol (by volume) reduces the surface tension of the mixture and eliminates bubble formation on the conducting glass surface during deposition. To demonstrate the importance of film uniformity, the ZnO films are employed in ZnO–Cu₂O n–p heterojunctions and an order of magnitude improvement in diode behaviour is observed.     

Synthesis, structure and photoelectrochemical performance of micro/nano-textured ZnO/eosin Y electrodes

Micro/nano-textured ZnO thick films were synthesized through deposition and pyrolysis of layered hydroxide zinc acetate (LHZA), Zn₅(OH)₈(CH₃COO)₂·2H₂O. LHZA films having a unique, rose-like morphology were initially deposited on conducting glass sheets in a chemical bath composed of methanol and zinc acetate dihydrate at 60 °C under neutral conditions. Pyrolysis of the LHZA films resulted in formation of ZnO without destroying the original morphology. Pyrolysis temperatures were found to greatly influence grain sizes and specific surface areas of the ZnO films. Photoelectrochemical performance of the films as ZnO/eosin Y electrodes was investigated in dye-sensitized solar cells using an I⁻/I₃⁻ redox electrolyte solution. The cell using the ZnO film pyrolyzed at 150 °C exhibited overall light to electricity conversion efficiencies of 2.0 and 3.3% under an AM-1.5 illumination at 100 and 10 mW cm⁻², respectively. While microscale pores in the electrodes facilitated mass transfer of fluid electrolytes in the depth direction, nanoscale pores contributed to an increase in the amount of adsorbed dye. The maximum incident photon-to-current conversion efficiency (IPCE) of the electrode reached 84.9% at a wavelength of 530 nm.     

Electrochemical properties of Cu2O/Cu composite particles prepared by a novel and facile method

Cu₂O/Cu composite particles were synthesized by a novel and facile chemical reduction method without any template or surfactant. X-ray diffraction (XRD) results showed that the product mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Typical FE-SEM images indicated that the particles with an octahedral shape were Cu₂O. In addition, the electrochemical performance of the Cu₂O/Cu particles as the working electrode material in alkaline solution was systematically investigated. The particles showed a maximum discharge capacity of 222.9 mAh g⁻¹ at a discharge current density of 60 mA g⁻¹ and a high value of 109.1 mAh g⁻¹ after 50 charge–discharge cycles. The results of cyclic voltammetry demonstrated that the reaction between Cu₂O and Cu is the major electrochemical reaction during the charging and discharging process. The results of electrochemical impedance spectroscopy indicated that the formation of Cu₂O on the surface of Cu particles significantly increased the contact resistance and the charge transfer resistance of the electrode during the discharging process.     

CO<Subscript>2</Subscript> hydrogenation to methanol over Cu/ZnO catalysts synthesized via a facile solid-phase grinding process using oxalic acid

Reduced Cu/ZnO catalyst was synthesized through solid phase grinding of the mixture of oxalic acid, copper nitrate and zinc nitrate, followed by subsequent calcination in N₂ atmosphere without further H₂ reduction. The catalysts were characterized by various techniques, such as XRD, TG-DTA, TPR and N₂O chemisorption. Characterization results suggested that during the calcination in N₂, as-ground precursor (oxalate complexes) decomposed to CuO and ZnO, releasing considerable amount of CO, which could be used for in situ reduction of CuO to Cu^o. The in situ reduced O/I-Cu/ZnO catalyst was evaluated in CO₂ hydrogenation to methanol, which exhibited superior catalytic performance to its counterpart O/H-Cu/ZnO catalyst obtained through conventional H₂ reduction. The decomposition of precursor and reduction of CuO happened simultaneously during the calcination in N₂, preventing the growth of active Cu⁰ species and aggregation of catalyst particles, which was inevitable during conventional H₂ reduction process. This method is simple and solvent-free, opening a new route to prepare metallic catalysts without further reduction.     

EXAFS and XPS Investigations of Cu/ZnO Catalysts and Their Interaction with CO and Methanol

Several investigations have been carried out on Cu/ZnO catalysts by employing extended Xray absorption fine structure (EXAFS) and Xray photoelectron spectroscopy (XPS). EXAFS investigations of Cu/ZnO catalysts subjected to hydrogen reduction show the presence of Cu¹⁺ species and Cu microclusters. The proportion of Cu¹⁺ depends on the rate of increase of the reduction temperature and on the amount of alumina added. An XPS study of the interaction of CO with model Cu/ZnO catalysts prepared in situ in the electron spectrometer shows the formation of CO₂ ^-, CO₃ ^2- and C₂O₄ ^2- species, their proportion relative to CO increasing with the Cu¹⁺/Cu⁰ ratio. A study of the interaction of CH₃OH with Cu clusters deposited on ZnO films reveals reversible molecular adsorption and the formation of CH₃O on clean Cu clusters. If the Cu clusters are pretreated with oxygen, however, both CH₃O and HCOO^- species are produced. Model Cu/ZnO catalyst surfaces containing both Cu¹⁺ and Cu⁰ species show interesting oxidation properties. On a Cu⁰-rich catalyst surface, only the CH₃O species is formed on interaction with CH₃OH. On a Cu¹⁺rich surface, the HCOO^- ion is the predominant species.     

Insights into Cu2O thin film absorber via pulsed laser deposition

Cuprous oxide materials are of growing interest for optoelectronic devices and were produced by several chemical and physical methods. Here, we report on the structural, optical, and electrical properties of Cu_xO thin films prepared by the pulsed laser deposition technique. The substrate temperature, as well as the oxygen partial pressure in the deposition chamber, were varied to monitor the copper to oxygen ratio within the deposited films. The growth conditions were carefully optimized to provide the highest conductivity and mobility. Thus, 100 nm thick cuprous oxide films (Cu₂O) deposited at 750 °C exhibited a resistivity of 16 Ω?cm, high mobility of 30 cm²/(V?s), and a bandgap of around 2 eV. The film deposited at the optimized deposition parameters on Nb:STO (001) substrate with Au top electrode showed a photovoltaic response with an open circuit voltage of 0.56 V. These results path the way to efficient solar cells made with Cu₂O films via the pulsed laser deposition technique.     

Dye-sensitized solar cell performance and photocatalytic activity enhancement using binary zinc oxide-copper oxide nanocomposites prepared via co-precipitation route

Zinc oxide nanoparticles (ZnO NPs) and binary ZnO–CuO nanocomposites (ZnO–CuO NCs) were prepared through a simple chemical co-precipitation route. The influence of copper (Cu²⁺) ions concentration (0.03, 0.06, 0.09, and 0.12 M) on optical, morphological, structural, and elemental characteristics of the ZnO–CuO NCs was examined by appropriate characterization techniques. The visible light reactive CuO created absorption shift to red region that minimized band gap of the ZnO–CuO NCs. The concentration of Cu²⁺ ions produced appreciable impact on size of the ZnO–CuO NCs. The dye-sensitized solar cell (DSSC) constructed using ZnO–CuO NC photoanode with Cu²⁺ ions concentration of 0.06 M generated a conclusive solar to electrical energy transformation efficiency of 2.56%, which was a 2.2-times greater over the DSSC encompassed pristine photoanode of ZnO NPs. The electrochemical impedance spectroscopy analysis revealed the longer lifetime of the photogenerated electrons and reduction in the charge recombination rate in the ZnO_(0.44)–Cu_(0.06) NC photoanode based DSSC. Furthermore, the ZnO_(0.44)–Cu_(0.06) NC disclosed substantial photocatalytic activity towards methylene blue dye degradation that could be chiefly credited to its particles size induced visible light absorption property.     

Synthesis and enhanced bias-free photoelectrochemical water-splitting activity of ferroelectric BaTiO3/Cu2O heterostructures under solar light irradiation

Here, we first use a facile electrochemical deposition method to load Cu₂O nanoparticles onto the BaTiO₃ (BTO) surface to prepare BTO/Cu₂O heterostructure photoanodes. Compared to the pure BTO photoanode, all BTO/Cu₂O heterostructure photoanodes show outstanding visible light harvesting ability and greatly improved photoelectrochemical water splitting performance. By optimizing the loading amount of Cu₂O nanoparticles, the photocurrent density achieved by BTO/Cu₂O-100 photoanode is 0.26 mA/cm² at 0 V versus Ag/AgCl, which is 2.6 times that of the bare BTO photoanode. In contrast with the photocurrent densities of the other reported BTO-based heterostructure photoanodes, the photocurrent density achieved by the present BTO/Cu₂O-100 photoanode without bias voltage is much higher. Additionally, the maximum solar-to-hydrogen conversion efficiency of the BTO/Cu₂O-100 heterostructure photoanode is 0.11% at 0.72 V versus reversible hydrogen electrode, approximately double that of BTO photoanode. The measurements of diffuse reflectance spectra, photoelectrochemical impedance and the room temperature photoluminescence spectra demonstrate that the improved photoelectrochemical performance contributes from the visible light absorption ability of Cu₂O nanoparticles, efficient transport and separation of photogenerated electron-hole pairs, which are induced by the spontaneous polarization electric field of ferroelectric BTO, p-n junction and type-II band alignment of BTO/Cu₂O heterostructure photoanode. A possible mechanism for the improved photoelectrochemical water splitting performance and charge transfer process is proposed.     

Dehydrogenation of cyclohexanol on Cu–ZnO/SiO2 catalysts: The role of copper species

For the dehydrogenation of cyclohexanol a series of Cu–ZnO/SiO₂ catalysts with various Cu to ZnO molar ratios was prepared using the impregnation method, with the loading of copper fixed at 9.5 at.%. The catalysts were characterized by XPS, H₂–N₂O titration, BET, H₂-TPR, NH₃-TPD and XRD techniques. The results indicate that the addition of ZnO can improve the dispersion of copper species on reduced Cu–ZnO/SiO₂ (CZS) catalysts. Cu⁰ and Cu⁺ species were found on the reduced CZS catalysts surface, and the amount of Cu⁺ increased with the content of ZnO increasing. The addition of ZnO increased the acidity of the CZS catalysts. However, only Cu⁰ species can be found on the reduced Cu/SiO₂ (CS) catalyst surface. According to the reaction results, we found that the selectivity to phenol was related to the amount of Cu⁺ species, the Cu⁺ species should be the active sites for the production of phenol, the Cu⁰ is responsible for cyclohexanol dehydrogenation to cyclohexanone.     

Cu2O/rGO复合材料修饰阴极强化MFC产电脱氮性能及其机理

微生物燃料电池(MFC)在处理含硝酸盐(NO_3^--N)废水时具有同时产电和脱氮的潜力,寻找成本低且改善其产电脱氮性能的阴极修饰材料是MFC在含氮废水处理领域应用的关键。氧化亚铜/还原氧化石墨烯(Cu₂O/rGO)复合材料具有良好的电化学性能,在替代铂基材料提高MFC性能方面具有一定的应用前景。本研究通过还原法制备了Cu₂O/rGO复合材料,并对材料的结构和氧还原性能进行表征；同时,将其负载于阴极碳布后分析其电化学性能,并通过MFC的输出电压、功率密度和NO_3^--N的去除率探究Cu₂O/rGO阴极对MFC产电和脱氮性能的强化作用；通过对反硝化相关酶活性和胞外聚合物的测定,探究Cu₂O/rGO阴极强化MFC性能的机理。结果表明：Cu₂O/rGO复合材料具有大量的介孔结构,能够为电子传递提供更多的通道,并且Cu₂O/rGO复合材料具有良好的氧化还原可逆性；与Pt/C阴极相比,Cu₂O/rGO阴极的交换电流密度升高33.53%,电子转移阻力降低65.53%；Cu₂O/rGO-MFC在处理NO_3^-N废水时获得的最大平均输出电压(662.54 mV)、最大功率密度(26.27 mW/cm^₂)、平均库伦效率(32.02%)和NO_3^--N去除速率(83.33 mg NO_3^--N L/h)均高于Pt/C-MFC(485.33 mV,16.98 mW/cm^₂,7.38%,41.67 mg NO_3^--N L/h)；Cu₂O/rGO复合材料通过提高MFC阴极反硝化关键酶活性和类蛋白组分含量,改善了MFC的产电和脱氮性能。     

Metal-organic framework stabilizes Cu7S4-wrapped Cu2O heterostructure for photothermal-promoted methanol/water reforming into hydrogen

To realize highly efficient in situ release of hydrogen energy from methanol reforming at lower operation temperature, the introduction of solar energy can effectively activate the methanol and significantly reduce activation energy of reaction. Herein, the hierarchical integration of photoactive Cu₂O/Cu₇S₄ core-shell nanospheres stabilized by MIL-101(Cr) support for H₂ evolution from photothermal-driven aqueous phase reforming of methanol afforded nearly sixfold enhanced performance compared with thermocatalytic process. Impressively, the photothermal effect conferred the Cu₂O/Cu₇S₄@MIL-101(Cr) with unprecedented activity at low temperature subside to 100°C and accelerated the activation of water and methanol with distinctly decreased activation energy from 103.9 to 66.6 kJ·mol⁻¹. Meanwhile, the enhanced catalyst stability and facilitated charge separation between Cu₂O/Cu₇S₄ and MIL-101(Cr) also contribute to the extraordinary photothermal-enhanced H₂ evolution with an overall turnover number of up to 14,266 in 60 h (apparent quantum efficiency of 25.08% at 365 nm), almost 10,000 times higher than that of Cu₂O/Cu₇S₄.     

Effects of Cu–Zn phases on electronic properties in ZnO:Cu films

Theory predicts Cu-doped ZnO (ZnO:Cu) has p-conductivity; however, this has only been demonstrated in a small number of experimental and mechanistic studies. In this paper, ZnO:Cu films were grown in situ with varying Cu content, prepared using radiofrequency atomic source–assisted molecular-beam vapor deposition. The results indicate that ZnO:Cu films with dopant of Cu²⁺ only had n-type behavior. As the Cu content increased, Cu⁺ was the major dopant and the ZnO:Cu films had p-type behavior. However, excess Cu dopant resulted in the formation of second phases of Cu₂O and Cu–Zn. The formation of a Cu–Zn phase increased the content of Zn vacancy, thus increasing hole concentration. Stronger alloy scattering decreased carrier mobility. Therefore, Cu⁺ dopant and Zn vacancy give ZnO:Cu films p-conductivity properties.     

Efficiency enhancement of non-selenized Cu(In,Ga)Se2 solar cells employing scalable low-cost antireflective coating

In this study, a non-selenized CuInGaSe₂ (CIGS) solar device with textured zinc oxide (ZnO) antireflection coatings was studied. The ZnO nanostructure was fabricated by a low-temperature aqueous solution deposition method. With controlling the morphology of the solution-grown tapered ZnO nanorod coatings, the average reflectance of the CIGS solar device decreased from 8.6% to 2.1%, and the energy conversion efficiency increased from 9.1% to 11.1%. The performance improvement in the CuInGaSe₂ thin-film solar cell was well explained due to the gradual increase of the refractive index between air and the top electrode of solar cell device by the insertion of the ZnO nanostructure. The results demonstrate a potential application of the ZnO nanostructure array for efficient solar device technology.     

Electrolytic synthesis and properties of potassium oxalatotungstate (V)

For deposition of thin films of electrochromic WO₃ on NESA glass from an aqueous solution of K[WO₂(C₂O₄)]·xH₂O, this compound is needed in a very pure form. The electrolytic reduction of a solution of tungstate(VI) in the presence of oxalate can overcome the disadvantages of the chemical reduction method. In this paper, an improved electrolytic reduction method is described, although a well-crystallized solid could not be obtained. Spectroscopic and conductometric measurements suggest that the chemical deposition proceeds in three steps.     

Sonochemical synthesis of crystalline nanoporous zinc oxide spheres and their application in dye-sensitized solar cells

A composite material made of zinc oxide and polyvinyl alcohol was prepared by a sonochemical method. Annealing of the composite under air removed the polymer, leaving porous spheres of ZnO. This change was accompanied by a change of the surface area from 2 m²/g to 34 m²/g. The porous ZnO particles were used as the electrode material for dye-sensitized solar cells (DSSCs). It was tested by forming a film of the doped porous ZnO on a conductive glass support. The performance of the solar cell is reported.