薄膜太阳电池系列讲座（7）CIGS薄膜太阳电池(中)

二CIGS薄膜太阳电池的结构和原理CIGS薄膜太阳电池是一种异质结型化合物半导体多晶薄膜太阳电池.CIGS材料的导电原理有其本身的特点.缺陷态即结构的不完整性,决定着CIGS的导电率和导电类型.而结构的完整性又与制备工艺和元素配比的控制密切相关,这就决定了工艺的难度,也就成为研究的重心.     

生物基底材料上纳米金薄膜导电、传热性能研究

利用瞬态电热技术测量了不同生物基底材料的热扩散率。通过增加镀层数目,采用微分测量法进行实验,根据实验结果计算了相应基底材料上厚度为5.00～20.00nm金薄膜的洛伦兹数、导热系数以及导电系数。研究结果表明,由于晶格边界散射大大减小了薄膜的导电和导热系数,所有基底上金薄膜的导热和导电系数均小于体材料金的导热和导电系数。由于蚕丝中的蛋白晶体可促进电子跳跃并产生隧道效应,蚕丝基底上金薄膜的导电系数大于其他几种基底上金薄膜的导电系数,因此蚕丝更适合作为柔性电子器件中的基底材料。     

稀土元素(Gd,Y)掺杂CdS薄膜的制备及其性能研究

采用化学水浴法两次沉积CdS,结合电子束真空蒸发法在两层CdS之间引入稀土层,制备含有不同厚度稀土Gd、Y掺杂层的CdS多晶薄膜。利用XRD、SEM、EDX、UV-VIS透射光谱和霍尔效应测试仪对薄膜的晶型、表面形貌、化学组成、光学及电学性能进行研究。结果表明:未掺杂的薄膜为沿(111)晶面择优生长的立方相闪锌矿结构,导电类型为n型。含有稀土Gd(Y)掺杂层的CdS多晶薄膜为立方相和六方相的混合结构,导电类型仍为n型,薄膜的均匀性和致密性得到改善,薄膜中Cd和S的原子比更接近CdS的化学计量比,稀土掺杂可提高CdS薄膜在可见光范围内的透过率,使薄膜载流子浓度增大、导电性能明显增强。     

太阳电池用共掺杂ZnO透明导电薄膜的结构及性能

采用直流磁控溅射法在室温条件下制备出Al,Zr共掺杂ZnO透明导电薄膜.用XRD和SEM分析和观察了薄膜的组织结构和表面形貌,着重分析了靶基距对薄膜结构和光电性能的影响.研究结果表明,制备的Al,Zr共掺杂ZnO透明导电薄膜为具有C轴择优取向、六角纤锌矿结构的多晶薄膜.靶基距对Al,Zr共掺杂Zn0透明导电薄膜的结构和...     

In掺杂CdO透明导电薄膜的研究

通过磁控射频溅射的方法分别在石英玻璃基底上和硅111基底上沉积In掺杂CdO透明导电薄膜。利用XRD、紫外可见分光光度计和霍尔效应测量仪测试薄膜的结构、光学和电学性能。一定量的In掺杂可将CdO的光学吸收边从2.2 eV提高至3.4 eV,甚至更高。同时适量的In掺杂可明显改善CdO薄膜的电学性能,在提高其电子浓度的同时也降低电阻率,获得最低5.8×10~(-5)Ω?cm的电阻率,同时吸收边为3.24 eV的透明导电薄膜。In掺杂的CdO薄膜作为一种性能良好的薄膜材料有较好的发展前景。     

薄膜厚度对ZnO:Ti透明导电薄膜光电性能的影响

利用直流磁控溅射法在室温水冷玻璃衬底上制备出可见光透过率高、电阻率低的掺钛氧化锌(ZnO∶Ti)透明导电薄膜。SEM和XRD研究结果表明,ZnO∶Ti薄膜为六角纤锌矿结构的多晶薄膜,且具有c轴择优取向。讨论了薄膜厚度对掺钛氧化锌透明导电薄膜光学、电学性能的影响。当薄膜厚度为835nm时,薄膜具有最低电阻率3.34×10-4Ω.cm。所制备薄膜附着性能良好,在波长为500～800nm的可见光中平均透过率均超过91%,ZnO∶Ti薄膜可用作薄膜太阳电池和液晶显示器的透明电极。     

在电共沉积GaAs薄膜上制作肖特基势垒的研究

应用化学电共沉积法在Ti片、导电玻璃和导电PI基片上制备了GaAs多晶薄膜,并在薄膜上应用电子束蒸发淀积了一层超薄的SiOx,然后采用PVD法在其上淀积一层金属薄层,制备出MIS结构的肖特基势垒。经测试Ag-SiOx-nGaAs结构和Au-SiOx-nGaAs结构的I-V特性,表明所制备的肖特基势垒具有良好的整流特性。     

有机薄膜衬底ITO透明导电膜的制备及光电特性的研究

采用真空反应蒸发技术,在有机薄膜基片上制备出高质量的ITO透明导电薄膜,对薄膜的结构和光电特性进行了研究.制备的最佳薄膜在可见光范围的平均透过率达84%,电阻率为8.23×10-4Ωcm,载流子浓度为1.72×1020cm-3.     

热处理气氛对Cd2SnO4透明导电膜化学态结构和电导率的影响

研究了热处理气氛对用无电沉积方法制备的Ｃｄ２ＳｎＯ４导电膜的化学态结构和导电率的影响。Ｘ射线光电子能谱和室温电阻率测量结果表明，以氢气为热处理气氛时，薄膜中的氧空位最高，导电性好，真空处理次之，以氧气为热处理气氛时，氧空位少，薄膜的导电性能差。     

RPD技术生长ICO∶H薄膜及其在晶体硅异质结太阳电池中的应用

通过反应等离子体沉积(RPD)技术室温下生长掺铈的氧化铟薄膜,且沉积过程中通入氢气。高迁移率可使透明导电薄膜在较低的电阻率时保持较高的近红外透过率;透明导电薄膜中较低的载流子浓度能够减少自由载流子的吸收。迁移率的大小主要由薄膜内的散射机制决定,并且受薄膜非晶结构制约。ICO∶H薄膜表面平整,在近红外长波段透过率超过80%。在氢气流量为2 sccm时,薄膜获得1.34×10^-3Ω·cm的最低电阻率和94 cm²/Vs的高迁移率。在晶体硅异质结(SHJ)太阳电池应用中,获得了较高的短路电流密度38.44 mA/cm²,相应的转换效率为16.68%。     

CdTe多晶薄膜太阳电池的结构改进

采用共蒸发法制备了ZnTe：Cu和Cd1-xZnxTe多晶薄膜，研究了薄膜的结构和性能。获得了Cd1-xZnxTe多晶薄膜的光能隙与锌含量的关系，ZnTe：Cu多晶薄膜光能隙随着掺Cu浓度的增加，光能隙减小。分别用ZnTe／ZnTe：Cu和Cd1-xZnxTe／ZnTe：Cu复合层作为背接触层，既能修饰异质结界面，改善电池的能带结构，又能防止cu原子向电池内部扩散。获得了面积0．5cm^2，转换效率为13．38％的CdTe多晶薄膜太阳电池。     

Characterization of CuInS2 thin films prepared by electrodeposition and sulfurization with photoluminescence spectroscopy

Potentiostatic electrodeposition and sulfurization techniques were used to prepare polycrystalline CuInS₂ thin films. X-ray diffraction and photoresponse measurements in a photoelectrochemical cell (PEC) revealed that photoactive polycrystalline CuInS₂ films can be deposited on Ti substrate. Photoluminescence (PL) spectroscopy was used to investigate the prepared thin films and optically characterize them. PL spectra revealed the defect structure of the samples with an acceptor energy level at 109 meV above the valance band and a donor energy level at 71 meV below the conduction band. The CuInS₂ thin films prepared in this investigation are observed to be In-rich material with n-type electrical conductivity.     

Preparation and characterization of thin films of electrodeposited CdTe semiconductors

Thin films of CdTe semiconductors were prepared by electrodeposition technique in aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry. The potential regions for the formation of the n-CdTe and p-CdTe films were determined. The structure, composition and morphology characteristics of as-deposited thin films of CdTe grown on SnO₂/glass and CdS/SnO₂/glass were investigated by XRD, EDAX and SEM techniques. The optical properties were measured to determine the absorption coefficient and band gap values. The as-deposited CdTe films grown on SnO₂/glass contained free Te while those grown on CdS/SnO₂/Glass did not contain this phase. The CdTe has the cubic structure with strong (111) orientation. The EDAX analysis showed a nearly stiochiometric Cd:Te ratio. The band gap has a value of 1.48 eV, which is in a good accordance with those reported in the literature. The effect of annealing at 350 and 400°C after CdCl₂ treatment on the structure and morphology was also examined.     

Hydrogenation and annealing effect on electrical properties of nanostructured Mg/Mn bilayer thin films

Bilayer Mg/Mn thin films have prepared using thermal evaporation method at pressure 10⁻⁵ torr. Hydrogenation process has been done on pristine and annealed bilayer structure of films at different hydrogen pressure for half an hour. In case of annealed samples partially semiconductor nature is observed and conductivity of films found to decrease with hydrogen pressure and increased with annealing temperature. The XRD analysis shows microcrystalline nature of as-deposited films and after annealing it produce crystalline nature. After hydrogenation an additional peaks of magnesium hydride are also observed that suggesting the presence of hydrogen and hydrogen storage capacity of thin film bilayer structure. Optical band gap of annealed bilayer thin films found to increase with hydrogen pressure. It means hydrogenation process is capable to change bilayer structure from metallic to semi-conducting. The variation in relative resistivity is found nonlinear with time and increases with hydrogen pressure, due to the net effect of hydrogen absorption. Raman spectra show the decrease in intensity of peaks with hydrogen pressure that confirm the presence of hydrogen. Optical photographs are taken in reflection mode that shows a change of color from brown to dark black state with increasing hydrogen gas pressure. This dark black state may be used as solar thermal energy collector because black body is good absorber of heat.     

CuO/Pd composite photocathodes for photoelectrochemical hydrogen evolution reaction

CuO has been considered as a promising photocathodic material for photoelectrochemical (PEC) hydrogen evolution reaction (HER). In this work, CuO films were prepared by a facile and cost-effective method that involves solution synthesis, spin-coating and thermal treatment processes. The resulting CuO films had a monoclinic crystal structure with bandgap energy of 1.56 eV and a conduction band position of 3.73 eV below the vacuum level in borate buffer solution. The CuO films exhibited good PEC activity toward HER and the preparation conditions had great effect on the activity. The photoactivity of the CuO film decayed to approximately 19% of its original value after reaction for 10 h under illumination. The reduction of CuO to Cu₂O has been confirmed to be a parallel competitive reaction against HER. The mismatched band structure of the resulting CuO/Cu₂O heterojunction was believed to be the main cause of the decay of photoactivity. The photo-assisted electrodeposition method was developed to prepare CuO/Pd composite photocathode. The presence of Pd on CuO greatly increased the photocurrent especially at low overpotentials. In addition, the CuO/Pd composite exhibited significantly improved photostability compared to CuO. This work demonstrates the feasibility of increasing PEC activity and stability of CuO-based photocathodes by combining CuO with noble metal nanoparticles.     

Characterization of CdTe thin film—dependence of structural and optical properties on temperature and thickness

The X-ray diffraction analysis of vacuum-evaporated cadmium telluride (CdTe) films reveals that the structure of the films is polycrystalline in nature for the samples prepared at higher substrate temperatures. The crystallite size (D), dislocation density (δ) and strain () were calculated. The composition analysis was made by the energy dispersive X-ray analysis. It confirmed the equal distribution of Cd and Te elements in the CdTe films. The fundamental optical parameters like band gap and extinction coefficient are calculated from the transmission spectra. The possible optical transition in these films is found to be direct and allowed. The charge transport phenomenon appears to be space charge limited conduction. Various electrical parameters were determined from the I–V analysis.     

Characteristics of nanocrystalline CdS films fabricated by sonochemical, microwave and solution growth methods for solar cell applications

Nanocrystalline CdS was synthesized by sonochemical and microwave methods. Characterization of nano-CdS was carried out by optical absorption, X-ray diffraction, TEM, SEM and EDX. A hyperbolic band model was used to calculate a shift in energy over that of the band gap of bulk CdS. Colloidal films comprising of nanocrystalline CdS were fabricated by the dip coating method. A comparison of optical absorption of CdS films on indium tin oxide (ITO)/glass by sonochemical and microwave methods was made with solution grown CdS films on ITO/glass. A blue shift in energy level at the nanoscale is demonstrated by optical absorption, and X-ray diffraction of nano-CdS shows a cubic structure. Electron microscopy studies with an FE-SEM and TEM show a particle size of 15 nm and diffraction patterns show a crystalline nature. Overall reduction in optical absorption due to blue shift is expected to result in higher performance, especially in short-circuit currents in CdS/CdTe solar cells.     

Influence of CdCl2 treatment on structural and optical properties of vacuum evaporated CdTe thin films

In this article we have discussed the structural, optical properties of vacuum evaporated CdTe thin films before and after CdCl₂ treatment. The CdTe thin films were prepared by vacuum evaporation. Films were prepared under the vacuum of 10⁻⁶ Torr. The structural studies have been performed by the X-ray diffraction (XRD) technique. The XRD analysis of vacuum evaporated CdTe films reveals that the structure of films is polycrystalline in nature. However, the crystallinity has been improved after the CdCl₂ treatment as shown by an increase of the diffraction peak intensities. This is due to the enhancement in the atomic mobility of CdTe. The optical properties of the CdTe thin films have been studied by the spectrophotometer in the 300–800 nm wavelength range. It is observed that the optical band gap energy is highly dependent on CdCl₂ treatments. The optical transitions in these films are found to be direct and allowed.     

Optical properties of C60/a-C superlattice structures for solar cell applications

C₆₀/amorphous carbon superlattice structures were fabricated by shutter-controlled molecular beam deposition. The periodic structure of resulted films was confirmed by X-ray diffraction measurements. From the UV–vis reflectance/transmittance measurements, the energy shift of absorption edge was observed in the superlattice structures as a function of their well width. The carbon-based superlattice structure is the useful technique to control the band gap energy of carbon materials.     

Structural, compositional, and optical properties of electrochemically deposited stoichiometric CdSe thin films from non-aqueous bath

In the recent years, cadmium chalcogenide compounds have been extensively investigated because of their potential applications in solar energy conversion. Thin films of CdSe have been deposited onto the stainless steel and fluorine doped tin oxide (FTO) coated glass substrates using simple and inexpensive electrodeposition technique. The non-aqueous solvent ethylene glycol (CH₂OHCH₂OH) containing precursors of Cd and Se with ethylenediaminetetraacetic acid (EDTA) tetra sodium salt as a complexing agent is used to obtain stoichiometric deposits. Deposition potential was estimated from polarization curves and other preparative parameters such as bath temperature and concentration of solution were optimized. X-ray diffraction (XRD) analysis reveals that the films are polycrystalline with cubic structure. PEC study shows the CdSe films are photoactive. Optical absorption study shows the presence of direct transition with band gap energy 1.72 eV. The energy dispersive analysis by X-rays (EDAX) reveals that the substrate is well covered with large number of grains indicating compact structure. The average ratio of the atomic percentage of Cd:Se is 50.31:49.69, showing that the deposited films are almost stoichiometric.