CdS薄膜的制备及其在CdTe电池中的应用

CdTe薄膜电池是发展最快、应用前景最好的一类太阳能电池。CdS层是CdTe电池的窗口层材料,其薄膜质量直接影响电池的转换效率。本文介绍了化学水浴沉积(CBD)和闭空间升华(CSS)两种方法沉积CdS薄膜,并完成单电池器件的制备和测试。CSS方法制备的薄膜结晶较大,光学和电学性能好于CBD方法制备的薄膜,太阳能电池的光电转换效率达到10.9%。CSS方法镀膜速度快,真空环境工作,有利于大规模产业化应用。     

硝磷酸腐蚀的CdTe太阳电池性能

CdTe薄膜的腐蚀是制作CdS/CdTe光伏电池的重要技术之一,本实验采用硝磷酸溶液（硝酸1%＋磷酸70%＋去离子水29%）腐蚀CdTe薄膜,通过XRD测试发现在CdTe膜上生成了碲层.随后,在腐蚀后的CdTe薄膜上分别沉积了几种结构的背接触层,并制备出相应结构的CdTe太阳能光伏电池.通过电池的光、暗I-V和C-V特性测试,以ZnTe/ZnTe：Cu/Ni为背接触的小面积太阳电池,其性能优于其它背接触的电池.实验结果表明器件性能与碲的生成和铜的扩散密切相关.     

溅射制备CdS薄膜及其在CdTe电池中的应用

采用射频磁控溅射方法分别在石英玻璃和TCO玻璃上制备了不同厚度的CdS薄膜,研究了CdS薄膜厚度对薄膜结构和光学性质的影响。在不同厚度的CdS/TCO衬底上,进一步制备成CdTe薄膜太阳电池。结果表明,CdS薄膜厚度的增加有利于薄膜的生长与结晶;110nm的薄膜具有禁带宽度为2.41eV的最大值;测试电池性能,得到CdS厚度为110nm的电池具有11.42%的最高转换效率。     

CdTe多晶薄膜制备及后处理对CdS/CdTe界面的影响

采用近空间升华法分别在玻璃、CdS及CdS1-xTex衬底上沉积了CdTe多晶薄膜,通过原子力显微镜的观察和X射线衍射的分析,比较了它们的微结构。结果表明,用CdS和CdS1-xTex多晶薄膜作为衬底沉积的CdTe多晶薄膜结构与衬底相似,具有(111)面择优取向。通过对在不同氧分压下进行后处理的CdS/CdTe薄膜的断面及光能隙的研究,发现在氮氧(4∶1)气氛下后处理的薄膜CdS层明显减薄,这样的结果有利于改善CdTe太阳电池的光谱响应,增加载流子收集。我们认为氧在退火中促进了CdS/CdTe界面互扩散,扩散的结果不仅弥补了CdS、CdTe间的晶格失配,而且降低了界面的位错密度,并获得了面积为0.52 cm2,转换效率为13.38%的CdTe多晶薄膜电池。     

用大面积CdTe多晶薄膜制备太阳电池

在制备有SnO2:F透明导电膜和CdS的衬底上,用自行设计的设备,通过调节加热灯管的分布获得了较均匀分布的温场,制备了300 mm×400 mm的大面积多晶CdTe薄膜.经XRD和AFM分析,制备的CdTe多晶薄膜均匀致密,呈(111)择优取向.将薄膜分成小块,做成结构为CdS/CdTe/ZnTe/ZnTe:Cu的小面积太阳电池.经测试,薄膜各部分的制作的电池性能相近.     

ZnS/CdS单带差超晶格薄膜的制备及光学性质研究

为了提高CdTe太阳电池的效率,ZnS/CdS单带差超晶格被创新性地提出.用射频磁控溅射法制备了ZnS/CdS单带差超晶格薄膜,用SEM观察样品截面,分层清晰;测试了ZnS/CdS单带差超晶格薄膜的透过谱图,在300～800nm波长范围内存在4个明显的透过峰.相较于CdS单层膜与ZnS单层膜,ZnS/Cds单带差超晶格薄膜在可见光短波部分的光谱响应十分明显,说明Zns/Cds单带差超晶格薄膜的电子能带与光子吸收方式发生了明显的变化.理论上可以提高CdTe太阳电池的效率.     

CIGS薄膜太阳能电池缓冲层材料的研究进展

CIGS薄膜太阳能电池的缓冲层为低带隙CIGS吸收层与高带隙ZnO窗口层之间形成过渡,减少两者带隙的晶格失配和带隙失调,并可防止溅射ZnO窗口层时给CIGS吸收层带来损害等,对提高CIGS薄膜太阳能电池效率起了重要作用.介绍了CIGS薄膜太阳能电池缓冲层材料的分类和制备工艺,主要阐述了CdS、ZnS及In2S3薄膜缓冲层材料及化学水浴法、原子层化学气相沉积法、金属化合物化学气相沉积法等制备工艺的研究现状,最后指出CIGS太阳能电池缓冲层在制备工艺、环境保护及大规模工业化生产中遇到的问题,并展望了其发展方向.     

CdTe/CdS太阳电池光照和电子辐照研究

采用近空间升华法制备CdTe多晶薄膜,以ZnTe/ZnTeCu复合多晶薄膜作为背接触层,获得了转换效率为13.38%的CdTe/CdS太阳电池.用光强为100mW/cm2的卤钨灯对电池光照7天后,发现电池性能无明显变化.经能量为1.6MeV,辐照剂量为1013～1015电子/cm2的电子束辐照后,电池性能有不同程度的衰降,经真空150℃退火30min后,电池性能恢复到接近辐照前的水平.     

氮化硅减反射膜制备工艺对组织结构及折射率影响的研究

太阳能电池是一种清洁能源,近年来发展迅猛。减反射膜能大幅减少太阳能电池对光线的反射,从而提高电池光电转化率。为优化减反射效果,减反射膜设计多样,包括单层膜、双层膜、三层膜和多层膜,膜层不同对薄膜材料的折射率要求不同。氮化硅薄膜是一种优秀的硅基太阳能减反射膜,其折射率在1.78～2.5之间,调控范围广。本文采用脉冲激光沉积法制备氮化硅减反射膜,研究不同工艺参数对硅片上沉积的氮化硅薄膜性能的影响。     

CIGS薄膜太阳能电池吸收层制备工艺综述

CIGS薄膜太阳能电池具有高光吸收系数、高转化效率、高稳定性等优点,已经成为太阳能电池领域的研究热点。其小样品最高转化效率已达19.9%,可与多晶硅电池的转化效率(20.3%)媲美;其大面积电池组件转化效率一般在10%～15%范围内,根据各膜层材料组分及制备工艺的不同而有所变化。综述了CIGS薄膜太阳能电池吸收层的各种制备工艺及其产业化进程。     

Dependence of photovoltaic performance of solvothermally prepared CdS/CdTe solar cells on morphology and thickness of window and absorber layers

In the present work a new strategy for straightforward fabrication of CdS/CdTe solar cells, containing CdS nanowires and nanoparticles as a window layer and CdTe nanoparticles and microparticles as an absorber layer, are reported. CdS and CdTe nanostructures were synthesized by solvothermal method. X-ray diffraction analysis revealed that highly pure and crystallized CdS nanowires and nanoparticles with hexagonal structure and CdTe nanoparticles with cubic structure were obtained. Atomic force microscope and field emission scanning electron microscope images showed that CdS nanowires with length of several μm and average diameter of 35 nm, CdS nanoparticles with average particle size of 32 nm and CdTe nanoparticles with average particle size of 43 nm, were uniformly coated on the substrate by the homemade formulated pastes. Based on ultraviolet–visible absorption spectra, the band gap energies of CdS nanowires, CdS nanoparticles and CdTe nanoparticles were calculated 2.80, 2.65 and 1.64 eV, respectively. It was found that, the photovoltaic performance of the solar cells depends on thickness of CdTe and CdS films, reaching a maximum at a specific value of 6 μm and 225 nm, respectively. For such cell made of CdS nanowires and CdTe nanoparticles the V_OC, J_SC, fill factor and power conversion efficiency were calculated 0.62 V, 6.82 mA/cm², 59.7 and 2.53 %, respectively. Moreover, photovoltaic characteristics of the solar cells were dependent on CdTe and CdS morphologies. CdS/CdTe solar cell made of CdTe and CdS nanoparticles had the highest cell efficiency (i.e., 2.73 %) amongst all fabricated solar cells. The presented strategy would open up new concept for fabrication of low-cost CdS/CdTe solar cells due to employment of a simple chemical route rather than the vapor phase methods.     

Zn1-xMgxO能带结构及作为窗口层的CdTe薄膜太阳电池的SCAPS仿真应用

采用第一性原理广义梯度近似+U(GGA+U)方法计算了纤锌矿结构Zn_1-xMg_xO(ZMO)(0≤x≤0.25)合金的能带结构。计算表明: 随着Mg组分增加, ZMO化合物的导带底及费米能级均向真空能级方向移动, 带隙增宽。基于理论计算得到ZMO的能带结构参数, 使用SCAPS软件对ZMO作窗口层的CdTe薄膜太阳电池的性能进行了仿真模拟, 并将研究结果与CdS作窗口层的CdTe太阳电池的性能进行了比较。结果表明: Mg在ZMO中的含量0≤x≤0.125时, ZMO/CdTe太阳电池具有比CdS/CdTe太阳电池更高的开路电压和短路电流密度; ZMO的导带底高出CdTe导带底约0.13 eV时, CdTe薄膜太阳电池的转换效率最高, 达到18.29%。这些结果为高效率碲化镉薄膜太阳电池的结构设计和器件制备提供了理论指导。     

Effects of junction formation conditions on the photovoltaic properties of sintered CdS/CdTe solar cells

Microstructures and properties of sintered CdS films on glass substrates and sintered CdTe films on polycrystal CdS substrates have been investigated. The CdS films, which contained 9 wt % CdCl₂ as a sintering aid and were sintered at 650° C for 1 h in nitrogen, are transparent and have an average grain size of 15m and an electrical resistivity of 0.5cm. The CdTe films, which were coated on the sintered CdS substrate and were sintered above 610° C for 1 h in nitrogen, have a dense structure with an average grain size larger than 5m. All polycrystal CdS/CdTe solar cells were fabricated by this successive coating and sintering method. The sintering temperature of CdTe films on the sintered CdS films was varied from 585 to 700° C. Compositional interfaces and p-n juctions are formed during sintering. The highest solar efficiency (7.18%) was found in a solar cell made by sintering the composite layer of glass-CdS-CdTe at 625° C for 1 h. A fabrication temperature below 610° C resulted in poor solar cell efficiencies due to the porous structure of the CdTe films and above 650° C also resulted in poor efficiencies due to the formation of a CdS_1-x Te_x layer at the interface and a large p-n junction depth.     

A microstructural study on the surface and interface of CdTe/CdS solar cells

The surface and interface properties of CdTe/CdS solar cells, including interfacial mixing, surface and interface geometrical morphology, CdTe grain size and preferential crystal orientation of CdTe layers were studied using Auger electron spectroscopy (AES) depth profiling, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, optical reflectance (OR) and X-ray diffraction (XRD) techniques. The correlation between the surface and interface properties and CdTe/CdS solar cell performance was also investigated. AES depth profiling was used to analyse the interdiffusion between the CdTe and CdS layers. Atomic force microscopy (AFM) suggests that the interfacial geometrical morphology has a significant influence on the photovoltaic property of CdTe/CdS solar cells. Rough interfaces tend to increase the photovoltaic conversion efficiency of solar cells because of multiple reflections. X-ray diffraction shows that polycrystalline CdTe/CdS solar cells with higher efficiencies appear to be orientated with more (1 1 1) planes of CdTe parallel to the macrosurface, but CdTe single crystals with differently indexed surface planes show almost the same reflection behaviour. Further theoretical and experimental analyses are therefore needed to clarify this observation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Annealing effects on the chemical deposited CdS films and the electrical properties of CdS/CdTe solar cells

CdS layers grown by chemical bath deposition (CBD) are annealed in the oxygen and argon-hydrogen atmosphere respectively. It has been found that the open circuit voltage of the CdS/CdTe solar cell increases when the CBD CdS is annealed with oxygen before the deposition of CdTe by close spaced sublimation (CSS), while the performance of the solar cell decreases when the CBD CdS is annealed with argon-hydrogen. Electronic properties of the CdS films are investigated using X-ray photo-electron spectroscopy (XPS), which indicates that the Fermi level is shifting closer to the conduction band after annealing in the oxygen and consequently a higher open circuit voltage of the solar cell can be obtained.     

Effects of CdCl2 in CdTe on the properties of sintered CdS/CdTe solar cells

Sintered CdS films on glass substrates with low electrical resistivity and high optical transmittance have been prepared by a coating and sintering method. All-polycrystalline CdS/CdTe solar cells with different microstructures and properties of the CdTe layer were fabricated by coating a number of CdTe slurries, which consisted of cadmium and tellurium powders, an appropriate amount of propylene glycol and various amounts of CdCl₂, on the sintered CdS films and by sintering the glass-CdS-(Cd + Te) composites at various temperatures. The presence of more than 5 wt% of CdCl₂ in the (Cd + Te) layer enhances the sintering of the CdTe film and the junction formation by a liquid-phase sintering mechanism. A low sintering temperature results in poor densification of the CdTe layer and the CdS-CdTe interface, whereas a high sintering temperature results in a deeply buried homojunction. The optimum temperature for the sintering of the CdTe layer and for junction formation decreases with increasing amount of CdCl₂. All-polycrystalline CdS/CdTe solar cells with an efficiency of 10.2% under solar irradiation have been fabricated by a coating and sintering method using cadmium and tellurium powders for the CdTe layer.     

Study of in situ CdCl2 treatment on CSS deposited CdTe films and CdS/CdTe solar cells

Effect of in situ CdCl₂ treatment on the morphological, structural and electrical properties of CdTe films as well as on solar cell characteristics of CdS/CdTe junction has been investigated. XRD measurements show that the presence of CdCl₂ vapours induces 111 oriented growth in the CdTe films. CdCl₂ concentration required for this oriented growth is found to be directly proportional to the substrate temperature. SEM measurements show enhanced grain growth in the presence of CdCl₂. Spectral response of the CdCl₂ treated CdS/CdTe solar cells shows an enhanced CdS diffusion in to the CdTe, which results in an improved spectral response in UV range and a consequent reduction in the interface states density. A drastic reduction in the deep levels due to the CdCl₂ treatment, as seen in the photo-capacitance studies, has results in CdS/CdTe solar cells having efficiency >8%.     

Effect of CdCl2 annealing treatment on thin CdS films prepared by chemical bath deposition

In order to study the CdS recrystallization mechanism, a comparative study was carried out on thin films prepared by chemical bath deposition. The CdS films were annealed in air with or without a CdCl₂ coating layer. In-situ Raman spectra obtained during the annealing showed that both the air- and the CdCl₂-annealing did not cause rearrangement of the neighboring atoms in the CdS clusters below ~ 300 °C. CdS thin film was partially oxidated to CdO and CdSO₄ on the cluster surface when annealed in air. The oxides and the sulfur stoichiometric deficiency prevented the clusters to coalesce at higher temperatures. Coating thin CdS film with a thin CdCl₂ layer protected it from oxidation during annealing in air and promoted formation of Cl_S and V_Cd point defects in CdS. The anti-oxidation was attributed to the incorporation of a significant amount of Cl into CdS to form the Cl_S, which prevented the oxygen in-diffusion and chemical bonding during the annealing. The anti-oxidation at the CdS nano-crystalline surface and the point defects formed in the CdS promoted coalescence of the neighboring clusters without the need of long-range redistribution of the atoms. Large CdS grains with good crystalline quality formed through recrystallization during the CdCl₂ heat treatment, which provided the solid basis for the subsequent CdTe growth and high efficient CdS/CdTe solar cell fabrication.     

Physical properties of Bi doped CdTe thin films grown by CSVT and their influence on the CdS/CdTe solar cells PV-properties

The physical properties of Bi doped CdTe films, grown on glass substrates by the Closed Space Transport Vapour (CSVT) method, from different Bi doped CdTe powders are presented. The CdTe:Bi films were characterized using Photoluminescence, Hall effect, X-Ray diffraction, SEM and Photoconductivity measurements. Moreover, CdS/CdTe:Bi solar cells were made and their characteristics like short circuit current density (J_sc), open circuit voltage (V_OC), fill factor (FF) and efficiency (η) were determined. These devices were fabricated from Bi doped CdTe layers deposited on CdS with the same growth conditions than those used for the single CdTe:Bi layers. A correlation between the CdS/CdTe:Bi solar cell characteristics and the physical properties of the Bi doped CdTe thin films are presented and discussed.