多晶Hg~1-xCd~xTe薄膜电极/多梳氧化还原电对溶液的界面现象研究

测量了系列(1-x)值的电沉积多晶Hg~1-xCd~xTe薄膜电极在多硫氧化还原电对溶液中的交流阻抗和光电流光谱, 据此确定出不同(1-x)值时的平带宽度。当(1-x)值增大时, 平带电位正移, 禁带宽度变小, 导带位置下降(负移), 价带位置基本保持不变。系列Hg~1-xCd~xTe薄膜电极在多硫溶液中的开路光电压比由平带电位推算出的极限开路光电压低, 因此存在着提高实际开路光电压的潜力。     

多晶Hg_(1-x)Cd_xTe薄膜电极 多硫氧化还原电对溶液的界面现象研究

测量了系列(1-x)值的电沉积多晶Hg_(1-x)Cd_xTe薄膜电极在多硫氧化还原电对溶液中的交流阻抗和光电流光谱,据此确定出不同(1-x)值时的平带电位Φ(?)和禁带宽度E(?).当(1-x)值增大时,平带电位正移,禁带宽度E(?)变小,导带位置下降(负移),价带位置基本保持不变.系列Hg_(1-x)Cd_xTe薄膜电极在多硫溶液中的开路光电压比由平带电位Φ_(fb)推算出的极限开路光电压低,因此存在着提高实际开路光电压的潜力.     

多晶富镉Hg_(1-x)Cd_xTe的电沉积及Hg_(0.09)Cd_(0.91)Te薄膜的光电化学行为

本文研究了在酸性CdSO_4+HTeO_2~+6HgCl_2 电解液中多晶富镉Hg_(1-x),Cd_(?),Te(x>0.5)的电沉积过程,实现了三种离子在同一电位下共沉积的技术。对在钛基底上沉积出的薄膜进行XRD,SEM和EDAX分析,结果表明薄膜为闪锌矿型的多晶结构,分布均匀连续。考察了(1—x)=0.09时多晶薄膜在多硫氧化还原电对液中的光电化学行为,光强为100mW/cm~2时,短路光电流I_(sc)=1.88mA/cm~2,开路光电压V_(oc)=0.25V,填充因子F·F=0.22。由光电化学光谱所确定出的禁带宽度E_g=1.26eV,Mott-schottky曲线给出了电极的平带电位φfb为—1.26V(vs.SCE),从而得到开路光电压V_(oc)可能达到的最大值为0.49V。因此,多晶富镉Hg_(1-x)Cd_xTe薄膜是一种很有潜力的光活性电极材料。     

多相光催化分解H2S中阴离子表面活性剂对半导体催化剂CdS表面的影响

研究了在H₂S碱性溶液中,CdS粉末催化剂存在时,光催化分解H₂S释氢和生成硫反应。考察了阴离子表面活性剂——十二烷基硫酸钠(SDS)对催化剂的表面性质和催化活性的影响。通过模拟该反应体系,用电化学方法测定了单晶CdS电极在上述反应体系中加入SDS(浓度低于临界胶团浓度CMC值)后的平带电位的变化。结果表明:单晶CdS电极的平带电位,由于该体系加入SDS而正移,与n型多晶半导体CdS在加入SDS的H₂S碱性溶液中,光催化分解H₂S的释氢量减少相一致。并探讨了在该体系中,由于表面活性剂的阴离子与S^2-在单晶CdS电极表面上的竞争吸附,而引起单晶CdS电极的平带电位正移。     

含氟水溶液中电化学刻蚀氟化WO3薄膜电极增强可见光光电化学性能

报道了在含氟的酸性水溶液中, 对电沉积制备的WO3薄膜电极进行电化学刻蚀, 并采用光电化学、扫描电子显微镜(SEM)、X射线衍射(XRD)、光电子能谱(XPS)、紫外-可见漫反射光谱、光致发光(PL)等方法对电极进行了表征. 结果表明, 刻蚀使电极比表面积增大, 质量减少, 重要的是可使电极表面状态发生变化. 在相同催化剂质量和比表面积的条件下, 这种变化显著提高了WO3薄膜电极在可见光和紫外-可见光照下的光电转换性能. 机理研究表明, 电极光电化学性能提高可归因于刻蚀使电极表面发生氟化, 光生载流子表面复合中心数目减少, 平带电位负移. 刻蚀对电极的吸光性质和晶体结构等未检测出明显变化. 氟化电极在酸性中具有良好的光电化学稳定性.     

共吸附剂修饰TiO2薄膜电极

共吸附剂修饰纳晶TiO₂薄膜电极是目前染料敏化太阳电池研究的一个热点. 本文通过平带电势和电化学阻抗研究了二(3,3-二甲基丁基)次膦酸和鹅脱氧胆酸两种共吸附剂修饰对TiO₂薄膜电极的平带电势和电极表面钝化能力的影响及其在染料敏化太阳电池中的应用. 结果表明, 二(3,3-二甲基丁基)次膦酸能更有效地钝化TiO₂薄膜表面, 并使TiO₂薄膜平带电势负移. 电化学阻抗谱测试结果表明, 在染料敏化太阳电池中, 相对于鹅脱氧胆酸, 二(3,3-二甲基丁基)次膦酸能更显著地提高器件的电子寿命和开路电压.     

单晶硫化镉光电化学电池中光阳极特性的研究

测量了单晶CdS电极在多硫体系和铁氰体系溶液中的光极化特性和波长响应特性,并由此计算出转换效率、填充因子和禁带宽度等有关参数。测量了CdS电极在不同频率下的阻抗谱,复数平面图近似半圆,表明电极/电解液的界面结构可以用一个较简单的模型来描述。Mott-Schottky关系线性良好,外延到电位轴得到的平带电位与光极化曲线上电流换向点电位相符。还发现平带电位与溶液pH值之间存在线性关系,可以用电极表面的水化氧化物膜与溶液中的H_aq⁺离子存在某种平衡来解释。     

电化学还原预处理对BiVO_4薄膜电极光电化学氧化水性能的提高

在酸性水溶液中(pH=2.0),采用电化学还原(ER)方法对BiVO4薄膜电极进行预处理,并探讨了其对薄膜电极光电化学氧化水性能的影响.结果表明,这种预处理可显著提高电极的光电化学氧化水的性能,且具有良好的光电化学稳定性.利用扫描电子显微镜、X射线衍射、拉曼光谱、光电子能谱、紫外-可见漫反射光谱、荧光光谱、电化学阻抗谱及Mott-Schottky等方法对ER处理前后的电极进行了表征.结果表明,ER预处理使电极粗糙度增大,表面积增大约1.4倍;电极材料的晶型无明显变化,但V—O对称伸缩振动略有红移;表面Bi,V和O结合能变小,Bi3+部分被还原,Bi/V原子比增大;ER处理导致电极平带电位负移,光生载流子在薄膜电极/溶液界面转移速率加快,表面复合速率降低.这些变化和表面积增加是BiVO4电极光电化学性能提高的主要原因.     

一氧化碳在硫修饰铂电极上的吸附与电氧化研究(英文)

吸附硫通常被认为是表面化学反应毒物,然而少量的硫能够增强铂的一氧化碳(CO)电氧化活性.本文利用常规电化学手段及表面增强拉曼光谱研究了CO在硫修饰的铂表面的电氧化.对于溶液中的CO,其在硫修饰铂电极上的起始氧化电位最多可以比非修饰电极负移超过300 mV,而且在硫覆盖度低于0.6的条件下电位负移量随覆盖度增加而增大.这一电催化活性的增强也受溶液pH值的影响.在低硫覆盖度(小于0.3)下,吸附态的CO电氧化峰值电位比非修饰铂电极负移约40 mV.然而,在高硫覆盖度下,其峰值电位比非修饰铂电极正移近30 mV.表面增强拉曼光谱显示共吸附硫使Pt—CO振动频率显著红移.作者认为这些结果是由于吸附硫弱化Pt—CO键及阻化CO在铂表面的移动引起的.     

用汞(Ⅱ)络离子电位滴定法直接测定硫化物抗氧化缓冲溶液中的硫离子

1 引言通常的硫化钠处理液和排放液成份复杂、色度深,其硫离子测定采用一般的氧化法、比色法和直接电位法很难满足快速、准确、方便的要求。用硫电极作指示电极,Ag~+、Pb~(2+)、Cd~(2+)作滴定剂直接电位滴定的报道不少,但在硫化物抗氧化缓冲(SAOB)溶液中,Ag~+与其溶液中抗坏血酸发生氧化还原反应;Pb~(2+)、Cd~(2+)滴定终点电位突跃小,均不能满足测定要求。Hg~(2+)对硫电极能产生超Nernst响应,并且HgS沉淀非常稳定(K_(SP)=10~(-50)),用Hg~(2+)作滴定剂具有滴定电位稳定,终点电位突跃大的特点。但是Hg~(2+)与抗坏血酸发生氧化还原反应,所以此法在SAOB溶液中直接滴定受到限制。我们利用Hg~(2+)电位滴定的特点,采用Hg~(2+)-半胱胺酸(CySH)络离子作滴定剂,有效地降低了Hg~(2+)的氧化电位,使其在SAOB溶液中可直接电位滴定测定硫离子。2 实验部分2.1 主要仪器和试剂 PXJ-1型数字式离子计;217型双液接饱和甘汞电极;自制硫电极;喷泡式吸收器:基准Hg~(2+)溶液(3.119×10~(-3)mol/L,0.6755g氧化汞,5ml浓硝酸,用水稀释至1L);Hg~(2+)-CySH标准溶液(6.238×10~(-4)mol/L,100ml基准Hg~(2+)溶液,0.5gCySH,用水稀释至500ml);测定底液(0.25mol/L抗坏血酸,1mol/L氢氧化钠,0.01mol/L EDTA-Na).     

Soft X-ray characterization of Zn(1-x)Sn(x)O(y) electronic structure for thin film photovoltaics

Zinc tin oxide (Zn(1-x)Sn(x)O(y)) has been proposed as an alternative buffer layer material to the toxic, and light narrow-bandgap CdS layer in CuIn(1-x),Ga(x)Se(2) thin film solar cell modules. In this present study, synchrotron-based soft X-ray absorption and emission spectroscopies have been employed to probe the densities of states of intrinsic ZnO, Zn(1-x)Sn(x)O(y) and SnO(x) thin films grown by atomic layer deposition. A distinct variation in the bandgap is observed with increasing Sn concentration, which has been confirmed independently by combined ellipsometry-reflectometry measurements. These data correlate directly to the open circuit potentials of corresponding solar cells, indicating that the buffer layer composition is associated with a modification of the band discontinuity at the CIGS interface. Resonantly excited emission spectra, which express the admixture of unoccupied O 2p with Zn 3d, 4s, and 4p states, reveal a strong suppression in the hybridization between the O 2p conduction band and the Zn 3d valence band with increasing Sn concentration.     

Design of energy band alignment at the Zn(1-x)Mg(x)O/Cu(In,Ga)Se2 interface for Cd-free Cu(In,Ga)Se2 solar cells

The electronic band structure at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface was investigated for its potential application in Cd-free Cu(In,Ga)Se(2) thin film solar cells. Zn(1-x)Mg(x)O thin films with various Mg contents were grown by atomic layer deposition on Cu(In(0.7)Ga(0.3))Se(2) absorbers, which were deposited by the co-evaporation of Cu, In, Ga, and Se elemental sources. The electron emissions from the valence band and core levels were measured by a depth profile technique using X-ray and ultraviolet photoelectron spectroscopy. The valence band maximum positions are around 3.17 eV for both Zn(0.9)Mg(0.1)O and Zn(0.8)Mg(0.2)O films, while the valence band maximum value for CIGS is 0.48 eV. As a result, the valence band offset value between the bulk Zn(1-x)Mg(x)O (x = 0.1 and x = 0.2) region and the bulk CIGS region was 2.69 eV. The valence band offset value at the Zn(1-x)Mg(x)O/CIGS interface was found to be 2.55 eV after considering a small band bending in the interface region. The bandgap energy of Zn(1-x)Mg(x)O films increased from 3.25 to 3.76 eV as the Mg content increased from 0% to 25%. The combination of the valence band offset values and the bandgap energy of Zn(1-x)Mg(x)O films results in the flat (0 eV) and cliff (-0.23 eV) conduction band alignments at the Zn(0.8)Mg(0.2)O/Cu(In(0.7)Ga(0.3))Se(2) and Zn(0.9)Mg(0.1)O/Cu(In(0.7)Ga(0.3))Se(2) interfaces, respectively. The experimental results suggest that the bandgap energy of Zn(1-x)Mg(x)O films is the main factor that determines the conduction band offset at the Zn(1-x)Mg(x)O/Cu(In(0.7)Ga(0.3))Se(2) interface. Based on these results, we conclude that a Zn(1-x)Mg(x)O film with a relatively high bandgap energy is necessary to create a suitable conduction band offset at the Zn(1-x)Mg(x)O/CIGS interface to obtain a robust heterojunction. Also, ALD Zn(1-x)Mg(x)O films can be considered as a promising alternative buffer material to replace the toxic CdS for environmental safety.     

How does back-reaction at the conducting glass substrate influence the dynamic photovoltage response of nanocrystalline dye-sensitized solar cells?

In dye-sensitized nanocrystalline solar cells (DSC), the transfer of electrons from the conducting glass substrate to triiodide ions in solution is an important loss mechanism that can be suppressed by using thin compact blocking layers of TiO(2). Whereas back-reaction at the substrate is relatively unimportant under short circuit conditions, it must be taken into account at the maximum power point or at open circuit. The influence of the back-reaction on open circuit photovoltage decay measurements and on intensity modulated photovoltage (IMVS) measurements has been studied by model simulations and by experimental measurements. The simulations demonstrate that reliable information about DSC properties such as trapping distributions can only be derived from transient or periodic photovoltage responses if the back-reaction is suppressed by the use of suitable blocking layers.     

The effects of pyridine derivative additives on interface processes at nanocrystalline TiO2 thin film in dye‐sensitized solar cells

2‐Methyl‐4‐propoxypyridine, a new pyridine derivative, has been synthesized and used as an additive in the liquid electrolyte of dye‐sensitized solar cells (DSSCs). Compared with 2‐methylpyridne and 4‐tert‐pyridine, they were employed to study the influence of the pyridine derivative additives on the rate of recombination at the electrode/dye/electrolyte interfaces and band edge shift of TiO₂, which were measured by time‐resolved mid‐infrared absorption spectroscopy and Mott–Schottky analysis, respectively. It was found that the rate of interfacial charge recombination was enhanced when the pyridine derivative additives were present in the electrolyte. Meanwhile, the additives caused a negative shift of the band edge. However, the net effect of pyridine derivative addition was to improve the open‐circuit photovoltage according to the photoelectrochemical measurement, indicating that negative shift of conduction band of TiO₂ was a predominant factor in improving the open‐circuit photovoltage. Also, the result was strongly supported by the dark current measurement. Therefore, it provides a microscopic account for the function of the pyridine derivative additives on the open‐circuit photovoltage enhancement of the DSSCs. Furthermore, the decrease of the short‐circuit photocurrent of the cells was also attributed to the slower dye regeneration due to the addition of additives from the results of cyclic voltammetry measurement. Copyright © 2007 John Wiley & Sons, Ltd.     

Photovoltaic properties of Pt/BiFeO3 thin film/fluorine-doped tin oxide capacitor

We study the photovoltaic properties of the Pt/BiFeO₃ (BFO) thin film/fluorine-doped tin oxide capacitor and obtain the open circuit voltage (V _oc) of 0.44 V and short circuit photocurrent (J _sc) of 0.14 mA/cm² under purple laser illumination. As compared to the BFO film with random orientations, the BFO film with a strong preferred orientation exhibits larger photovoltaic output as a result of its larger spontaneous polarization in the unpoled state. We further demonstrate that there is remarkable influence of external electric field poling on the photovoltage in the two polycrystalline BFO films, and the larger net change of the photovoltage after positive and negative poling in the highly preferred oriented BFO film is believed to be due to its improved crystalline structure. Our experiment results indicate that the responsiveness to external electric field and photovoltaic performance of the narrow-band-gap BFO film can be optimized by structural modification, making it possible to apply in the photosensitive and other optoelectronic devices.     

Photovoltaic Behaviour of Titanyl Phthalocyanine Thin Films and Titania Bilayer Films

Summary: Titanyl phthalocyanine (TiOPc) thin films were prepared using evaporation and surface polymerization by ion-assisted deposition (SPIAD) in a vacuum deposition system. These films were characterized by means of ultraviolet and X-ray photoelectron spectroscopy as well as UV/Vis absorption spectroscopy. Valence band and elemental content indicated that phthalocyanine electronic and chemical structures were largely preserved during SPIAD. Further, bilayer thin films of titania (TiO₂) and SPIAD TiOPc were prepared. TiO₂ film was deposited by reactive magnetron sputtering of TiO₂ target. Study of the structured samples was focused on the optical and electrical properties of the composite films. The films were characterized by non-contact photovoltage measurements and UV-Vis spectroscopy. These results suggest there is a possibility to use these bilayer thin films in photovoltaic solar cells, however further experiments to improve conductivity of the films will be required.     

Controllable synthesis of ZnxCd1-xS@ZnO core-shell nanorods with enhanced photocatalytic activity

We report the synthesis of Zn(x)Cd(1-x)S@ZnO nanorod arrays via a facile two-step process and the implementation of these core-shell nanorods as an environmental friendly and recyclable photocatalyst for methyl orange degradation. The band gap of Zn(x)Cd(1-x)S@ZnO core-shell nanorods can be readily tunable by adjusting the ratio of Zn/Cd during the synthesis. These Zn(x)Cd(1-x)S@ZnO core-shell nanorods exhibit a high photocatalytic activity and good stability in the degradation of the methyl orange. Moreover, these films grown on FTO substrates make the collection and recycle of the photocatalyst easier. These findings may open new opportunities for the design of effective, stable, and easy-recyclable photocatalytic materials.     

A methodology for investigating new nonprecious metal catalysts for PEM fuel cells

This paper reports an approach to investigate metal-chalcogen materials as catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells. The methodology is illustrated with reference to Co-Se thin films prepared by magnetron sputtering onto a glassy-carbon substrate. Scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) have been used, in parallel with electrochemical activity and stability measurements, to assess how the electrochemical performance relates to chemical composition. It is shown that Co-Se thin films with varying Se are active for oxygen reduction, although the open circuit potential (OCP) is lower than for Pt. A kinetically controlled process is observed in the potential range 0.5-0.7 V (vs reversible hydrogen electrode) for the thin-film catalysts studied. An initial exposure of the thin-film samples to an acid environment served as a pretreatment, which modified surface composition prior to activity measurements with the rotating disk electrode (RDE) method. Based on the SAM characterization before and after electrochemical tests, all surfaces demonstrating activity are dominated by chalcogen. XRD shows that the thin films have nanocrystalline character that is based on a Co(1-x)Se phase. Parallel studies on Co-Se powder supported on XC72R carbon show comparable OCP, Tafel region, and structural phase as for the thin-film model catalysts. A comparison for ORR activity has also been made between this Co-Se powder and a commercial Pt catalyst.     

Band-gap engineering of metal oxides for dye-sensitized solar cells

Mixed oxides Ti(1-x)Zr(x)O2 with 0 < x < or = 0.2 were synthesized by means of thermal hydrolysis for use in dye-sensitized solar cells. The lattice parameter d is observed to increase linearly with Zr content x. The band gap of the mixed oxides was measured to increase by up to 0.2 eV. The respective shift of the conduction band edge leads to an increase of the open circuit voltage (V(OC)) by up to 0.1 V. Among others, temperature-dependent measurements of V(OC) clearly identify the correlation between band edge shift and change in V(OC).     

Energy Band Structure of Alq3/TCAQ Heterostructure Complex Film Determinedby Surface Photovoltage Spectroscopy (SPS)

IntroductionOrganic light--emitting diodes (OLEDs) have been extensively investigated since Tanget al. [l] reported a low-voltage high-efficient device in 198712'3]. It has been found that multilayer heterostructures have fascinating advantages in the whole selection of emission color, intensive brightness, high efficiency and relatively low operating voltage['--'J. It is important todetermine the energy band structure of the multilayered film, which will be helpful to interpret the electrol…