Photoelectrochemical cells with mixed polycrystalline n-type CdSPbS and CdSCdSe electrodes

The photoelectrochemical behaviour of n-type CdS (polycrystalline) containing small amount of PbS or CdSe in S^2? /S^2?_n redox system has been studied. Mixed polycrystalline n-type CdSPbS electrodes were prepared by electrodeposition and the n-type CdSCdSe electrodes were made by partial replacement of sulphide ions of CdS electrode with selenide ions from a solution of sodium selenosulphate. It has been observed that both the mixed chalcogenide electrodes exhibit better photoresponse than the simple CdS electrode.     

Photocurrent oscillations at photoanodes of CdS films

Photocurrent oscillations have been observed with CdS electrodes in contact with basic aqueous solutions, depending on the pH, the light power, the applied potential and the presence of various organic reductants; they are correlated with CdS chemical modifications.     

Photoelectrochemical properties of butane reduced flame-treated Zr-doped hematite thin films

In this research, Zr-doped hematite thin films were prepared by a simple and highly scalable liquid phase deposition method, and their photoelectrochemical (PEC) properties were investigated. The samples were post-heat treated using a butane reduced flame. PEC studies revealed that both Zr-doping and flame-treatment enhanced the performance of the hematite photoanodes. The photocurrent densities of the samples were considerably increased upon flame-treatment, that is, about 3.5 times for a 4% Zr-doped sample. The highest photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) was obtained, about 0.50 mA cm⁻² for the 4% Zr-doped sample, about five times higher than the undoped sample. The Mott–Schottky measurements revealed that the donor charge carrier density for the 4% Zr-doped sample was increased fivefold upon flame-treatment from 2.49 × 10¹⁹ to 1.38 × 10²⁰ cm⁻³. The optical investigations showed that the optical band gap energy values depend on the level of Zr-doping, and the sample with 4% Zr-doping showed the lowest band gap energy value, about 1.82 eV. The mechanism behind the effectiveness of the flame-treatment was investigated and attributed to the oxygen vacancy formation upon flame-treatment. The formation of oxygen vacancies activates the donor doping, and as a result, the charge carrier density increases. In general, butane reduced flame-treatment as a simple and effective strategy can be used as a post-heat treatment to boost the PEC properties of hematite thin films.     

Photoelectrochemical behavior of thin, thermally grown polycrystalline Fe2O3 films

The photoelectrochemical behavior of a number of photoelectrodes prepared in polycrystalline form from 99.9% iron (Armco) under controlled thermal oxidation conditions is reported. The steady-state polarization curves show a complicated aspect corresponding to changes in the charge transfer kinetics. A strong influence of the surface oxide thickness (d) on both the electrochemical characteristics and the photocurrent efficiency is found. Maximum photocurrents are measured on oxide covered electrodes with d < 10⁴ Å. The long term stability of the electrodes covered with oxide layers of thickness less than 10³ Å is unsatisfactory.     

Photoelectrochemical properties of Ni-doped Fe2O3 thin films prepared by electrodeposition

Ni-doped Fe₂O₃ thin films which were active photoanodes for water splitting were prepared by electrodeposition. By adjusting Ni molar ratios (Ni/(Ni + Fe)) in the electrolyte, Fe₂O₃ thin films with various compositions of Ni could be tuned. The films were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic absorption spectrophotometer, and UV–vis spectroscopy. The highest photo-response obtained from Fe₂O₃ doped with 2.08 mol.% Ni is 1.5 mA/cm² at 0.65 V vs. Ag/AgCl in 1.0 M NaOH solution. The high performance is attributed to the improvement of charge transport properties and retardation of the charge recombination resulting from the dopants in the lattice. The optical absorption spectra of the films reveal that the bandgaps of the Ni-doped Fe₂O₃ films are approximately 1.9–2.2 eV for all samples regardless of their doping level. XPS shows that the concentration of Ni is much higher on the surface than that in bulk.     

Photoelectrochemical properties of hematite thin films grown via a two-step electrochemical deposition method

In this study, Fe₂O₃ thin films were deposited via one-step and two-step electrochemical deposition methods. The one-step method used a constant growth potential, and the two-step method used two continuous growth potentials during the deposition. The morphological, electrical, and structural properties of the thin films and the relationships of each property with the photoelectrochemical properties of the thin films from the two methods were analyzed and compared. We determined that the samples grown by the two-step method have better photoelectrochemical properties than those grown by the one-step method. In this study, we attempted to determine the optimum growth potentials for the one-step and two-step methods and the growth durations of the first and second stages in the two-step method in terms of the photoelectrochemical properties. The sample formed at ?0.05 V for 30 s in the first step and ?0.25 V for 2 min 30 s in the second step in the two-step method has the highest photocurrent density value of 0.28 mA/cm² (at 0.5 V vs. SCE), which is higher than that of the samples grown by the one-step method.     

Photoelectrochemical solar cells fabricated from porous CdSe and CdS layers

Porous CdSe layers were prepared by spray pyrolysis deposition using sodium selenosulfate as a selenium source and its surface area and porosity were increased by the dissolution of sodium sulfate formed as by-product. The porous CdSe as both photoanode and absorber could efficiently transport electrons to fluorine-doped tin oxide electrode and extract holes to the electrolyte. The cells were optimized by controlling the number of spray pyrolysis deposition cycles and then etching with sodium sulfate. An efficient solar cell having a power conversion efficiency of 2.6% at 1 sun illumination (100 mW cm⁻¹) was fabricated. Further, we extend this approach to fabricate an efficient porous CdS-sensitized solar cell with power conversion efficiency greater than 1.0% at 1 sun illumination.     

Photoelectrochemical properties ofp-RuS2

An impedance study of thep-RuS₂/aqueous electrolyte interface confirms the existence of a Fermi level pinning of the semiconductor. The mechanisms of the band shift and of the interaction with a redox couple are illustrated. The photopotential is limited by the moderate quality of the barrier which allows forward currents flowing through the interface.The effect of the interface modification by means of a metal deposition on the semiconductor surface has been investigated. An improvement in the catalysis with respect to both photoassisted hydrogen evolution and oxygen dark reduction was found. Evidence for an insertion of hydrogen into p-RuS₂ is also presented.     

Electrochromic properties of polycrystalline thin films of tungsten trioxide prepared by chemical vapour deposition

The electrochromic properties of polycrystalline thin films of tungsten trioxide prepared by chemical vapour deposition were studied using cyclic voltametry and chronoamperometry measurements. Two kinds of films were investigated depending on the conditions of preparation. Although the composition of the layers obtained after pyrolysis of W(CO)₆ is influenced by the presence of oxygen flow, the final annealing of these products leads to the same polycrystalline structure. Electrochromic properties have been investigated in acid and hydro-organic electrolytes. Cyclic voltametry shows that both colouration and bleaching of the films are associated with electrochemical reactions. The optical efficiencies and the response times were studied in both media and compared with amorphous WO₃ thin films prepared by vacuum evaporation. Best results have been obtained in acid electrolyte for films prepared by pyrolysis of W(CO)₆ in the presence of oxygen flow. We also observed that cycling greatly enhanced the response time. Current injection during colouration was found to depend strongly on time and to be mainly controlled by the resistance of the electrolyte at short times (f<200 ms).     

Spray pressure variation effect on the properties of CdS thin films for photodetector applications

Herein, we report the photosensing property of CdS thin films. CdS thin films were coated onto glass substrates via a spray pyrolysis method using different spray pressures. Prepared films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical and photoluminescence spectroscopy. XRD analysis demonstrated the growth of crystalline CdS films with crystallite sizes varying from 26 to 29 nm depending on the pressure. The SEM and EDAX analyses revealed nearly-stoichiometric CdS films with smooth surfaces and slight variation in grain morphology due to pressure changes. Optical measurements showed a direct bandgap varying from 2.37 eV to 2.42 eV due to pressure changes. A photodetector was also fabricated using the grown CdS films; the fabricated photodetector exhibited good performance depending on the spray pressure. A spray pressure of 1.5 GPa resulted in high photoresponsivity and external quantum efficiency.     

Superconductivity in polycrystalline diamond thin films

Superconductivity was discovered in heavily boron-doped diamond thin films deposited by the microwave plasma assisted chemical vapor deposition (MPCVD) method. Advantages of the MPCVD deposited diamond are the controllability of boron concentration in a wide range, and a high boron concentration, especially in (111) oriented films, compared to that of the high-pressure high-temperature method. The superconducting transition temperatures are determined to be 8.7 K for T_c onset and 5.0 K for zero resistance by transport measurements. And the upper critical field is estimated to be around 7 T.     

Photoelectrochemical properties and microstructuring of polythiophenes

Photoelectrochemical microstructuring processes have been applied to various classes of semiconductors and especially to intrinsically conducting polymers such as polythiophenes. In this work, a new technique was developed for photoelectrochemical post-structuring of conducting polymers deposited on Pt and p-Si. The surface of a conducting polymer is illuminated with a focused laser beam in a non-aqueous solution in the presence of tetrabutylammonium (TBA) salts. This results in local photoelectrochemical cathodic doping of the polymer and corresponding conductivity increase. Poly-3-phenylthiophene (P3PhT) and polybithiophene (PBT) were investigated in this work. In the case of P3PhT, colourless conducting films are formed, and the post-structuring process could be visualised using conventional optical microscopy. The obtained micropatterns were stable in air and in the anodic doping region, but could be removed by repeated cycling in a potential range including both anodic and cathodic doping. The microstructures were characterised by SEM, EDAX, SECM and other techniques.     

Photoelectrochemical properties of bismuth oxyhalide films

The photoelectrochemical (PEC) properties of bismuth oxyhalide (BiOCl, BiOBr, and BiOI) electrodes prepared by anodic oxidation of bismuth films on a platinum substrate have been studied. In acidified potassium halide solutions, these electrodes have been found to exhibit the PEC properties characteristic of p-type semiconductors. The efficiency of the PEC process appreciably decreases in the series BiOCl> BiOBr> BiOI. Effective protectors of the BiOHal electrode photodecomposition are dissolved oxygen and hydroquinone/quinone redox pair. The spectral sensitization of BiOHal electrodes can be carried out by different dyes, the quantum efficiency of the sensitized process being relatively high (3–7%) in a number of cases. The ways of increasing the stability of sensitized PEC process on BiOHal electrodes are considered.     

MoS2 co-catalyst sensitized 3D TiO2/CdS photoanodes with enhanced photoelectrochemical performances

Regulating morphology and constructing heterojunctions to enhance the light absorption and boost the separation of electrons and holes are common and effective means to boost the photoelectrochemical (PEC) performances of TiO₂ photoanodes. In this study, TiO₂ nanoflowers (NFs)/CdS quantum dots (QDs)/MoS₂ nanosheets (NSs) hybrids with two type II band alignments were synthesized by facile hydrothermal, successive ionic layer adsorption and reaction, and dipping methods, respectively. The effects of different amount of MoS₂ co-catalysts on CdS decorated TiO₂ photoanodes were investigated. TiO₂ NFs/CdS QDs/MoS₂ NSs hybrids showed dramatically enhanced PEC performance, especially under visible light illumination. The photocurrent density of TiO₂ NFs/CdS QDs/MoS₂-50 was more than 10 times higher than that of TiO₂ NFs/CdS QDs. This innovative work sheds light on efficiently improving the light absorption by forming heterojunctions and accelerating the electron and hole transfer via specific band engineering design.     

CdS量子点敏化TiO2薄膜电极的制备和光电化学性能

用水热微乳法制备了结晶性良好的CdS量子点,并通过连接分子巯基乙酸将CdS量子点自组装到多孔TiO2薄膜电极上.结果表明:CdS纳米颗粒的平均直径约为5nm,小于其量子尺寸;微乳体系为化学反应提供了良好的微型反应器,抑制了CdS晶粒的长大,而水热过程增强了CdS纳米颗粒的结晶性;由于CdS的可见光响应作用和CdS量子点...     

硫化镉复合二氧化钛纳米管阵列光电化学研究

采用阳极氧化法在钛片表面制备出了内径约70 nm,管壁厚度约30 nm的整齐有序的TiO_2纳米管列阵,而后通过浸渍法得到Cd S复合的TiO_2纳米管阵列。XRD和SEM分析样品晶型以及形貌特征的结果表明,随着浸渍次数的增加,TiO_2纳米管阵列上复合的CdS的量也随之增加。利用电化学工作站测定样品光电转化性能,结果表明,在TiO_2纳米管阵列上适量地复合CdS可以有效提高其光电转化效率,并且在浸渍次数为2次时,复合TiO_2纳米管阵列具有最佳光电化学性能,与纯二氧化钛纳米管的光电流为0.26 m A/cm~2,太阳光转化率为0.95%相比较,其光电流可达到0.58 m A/cm~2,太阳光转化率可达到4.02%,分别高于纯二氧化钛纳米管的2倍和4倍。     

Photoelectrochemical properties of bismuth-doped titanium oxide electrodes

With the aim of obtaining TiO₂ films with increased photoresponse titanium metal was alloyed with bismuth and then directly oxidized. The free energy efficiencies of the Ti-Bi oxide increased four times by increasing the bismuth content up to 10 wt %. The spectral response of the Ti -Bi oxides was slightly shifted toward the visible region with respect to the response of TiO₂, and their E _g were observed to be in the range 2.87–3.0 eV.     

Photoelectrochemical study of oxygen deficient TiO2 nanowire arrays with CdS quantum dot sensitization

Oxygen-deficient TiO(2) nanowires show substantially increased donor density due to an increase in oxygen vacancies introduced intentionally by thermal treatment in ammonia, vacuum, or hydrogen. By coupling oxygen-deficient TiO(2) nanowires with CdS quantum dots, a significant enhancement in their photoactivities was observed in the entire wavelength region from 350 to 550 nm. These new nanocomposites hold great promise for solar hydrogen generation.     

多晶硅生产的节能降耗

多晶硅是光伏和半导体产业的重要原材料,介绍了我国多晶硅生产工艺及生产特点,从技术和管理的角度,论述了多晶硅生产节能降耗的必要性、途径和方法,探索集约型的多晶硅生产之路。